Virus and Mycoplasma Diseases of Fruit Crops in India

V.V:CHENULU

and Y.S.AHLAWAT Division of Mycology and Plant Pathology Indian Agricultural Research Institute New Delhi

~3I'jl

ICAR

PUBLISHED BY

PUBLICAnONS AND INFORMATION DIVISION

INDIAN COUNCIL OF AGRICULTURAL RESEARCH KRISHI'ANUSANDHAN BHA VAN NEW DELHI 110 012

Printed: February 1994

Director (P&/) Chief Editor Editor Assistant Editor Technical Associate Chief Production Officer Production Officer Senior Technical Assistant Chief Artist Senior Artist

DR V.S. BHATI

S.N. TATA DR (MRS) A. M. WADHWANI M. S. MElIor

R. P.

ARYA

D. S. BEDEKAR J. B. MEHRA M1L SETH

A.CHAKRA VARTY SURESH DHAWALE

© 1993, Indian Council of Agricultural Research, New Delhi

Price

Rs 50

Published by Dr,V.S. Bhatt, Director (P&I) for the Publications and Infonnation Division, Indian Council of Agricultural Research, Krishi Anusandhan Bhawan, Pusa, New Delhi 11 0 012 Lasenypeset at Rasleen An Printers, H- 80, West Patel Nagar, New DeUu 110008 and Printed at Allied Publishers Limited, A-I 04, Mayapuri, Phase II, New Delhi 110 064 .

CONTENTS

1.

INTRODUCTION

2.

VIRUS AND MYCOPLASMA DISEASES OF TEMPERA TE FRUITS 2 Virus and virus-like diseases of pome fruils Virus and mycoplasma diseases of stone fruiLS

2 7

3.

VIRUS DISEASES OF TROPICAL AND SUB-TROPICAL FRUITS

18

4.

VIRUS DISEASES OF OTHER FRUIT CROPS

48

5.

MANAGEMENT OF VIRUS AND MYCOPLASMA DISEASES OF FRUITS

52

Detection of pathogens Disease management Recommendations for management of viruses in nurseries Recommendations for virus management in orchard Future thrust

52 61 69 69

69

1 Introduction THE diseases of fruit crops caused by viruses and mycoplasma-like organisms are attracting increasing attention. This is because of the better understanding of the nature of viruses, and research has been done on large number of virus diseases affecting fruit crops during the last six decades. Many of the unknown diseases have been proved to be caused by viruses but still new diseases have appeared with alarming frequency, the origin of which is still unknown as for example declinio or blight disease of citrus in Brazil and Florida respectively. Virus diseases of fruits are comparatively more important due to their perpetuation through vegetative propagation which also help in wide spread of the disease in different geographic regions. Diseases caused by viruses, mycoplasma-like bodies and viroids are among the greatest threat to fruit industry all over the world. Viruses consist of either ribonucleic acid (RNA) or deoxyribonucleic acid (DNA) usually surrounded by a thin coat of protein. Mycoplasmas are pleomorphic, resembling 'L' forms of bacteria and are thousand time bigger than viruses. Mycoplasma contains both RNA and DNA, an,d has a complex structure surrounded by unit membranes. These organisms can. _produce themselves, whereas virus replication is dependent on the host and cannot multiply in vitro. A group of mycoplasmas belonging £0 £he genus Spiroplasma can be cultured in artificial media. The total land under agriculture in India is about 175 million hectares and horticultural crops cover about 11.4 million hectares, which is 6.5% of the total cropped area. Fruits and vegetables alone account for about 6.2 million hectares with production of about 55 million tonnes, values between Rs 50,000 and 70,000 million. Diseases and pests have a direct impact on the fruit industry in India. In earlier days the farmer used to grow fruits sufficient for his own consumption, but with the increase in population and demand for more fruits, the commercial fruit growing has become more profitable. At the same time the diseases and insect problems have also multiplied. Some diseases and pests were introduced from abroad, but many already existed in the country on wild or cultivated species. Better communication facilitated the spread of the parasitic organisms. The present-day consumer demands fruits of high quality and free of blemishes. This sometimes makes it difficult for the orchardist to dispose off his surplus crop in the year of abundant yield. Therefore these growers look more and more to the experiment stations and agricultural institutions for guidance in the production of marketable fruit. An attempt has been made in the following pages to collect and summarize the information on fruit diseases in India, which has accumulated for the last 40 years. This will provide a good guide to researchers and students concerned with fruit diseases in India or elsewhere.

2

Virus and Mycoplasma Diseases of Temperate Fruits INDIA has various types of agroclimates. We find all types of fruits-temperate, sub· tropical and tropical-grown on a commercial scale. Sub·tropical and tropical fruits are grown in almost all the states of the country but temperate fruits are restricted to Himalayan and sub·Himalayan tracts of the states of Jammu and Kashmir, Himachal Pradesh, Uttar Pradesh, Sikkim, West Bengal aIld north· eastern states. Some of the important virus and virus· like diseases of temperate fruits recorded so far in India are described below. VIRUS AND VIRUS-LIKE BISEASES OF POME FRUITS Our knowledge about the virus diseases of temperate fruits in general and pome fruits in particular is comparatively meagre. Characterization of viruses affecting these crops and their epidemiology has still to be studied in several cases. Among the pome fruits, apple is the main cash crop covering an area of 0.1537 million hectare and producing 0.927 million tonnes of fruits. Pear is another pome fruit widely cultivated in northern Indian hills and plains. Quince inestricted to northern Himalayas and is cultivated on a small scale. All these crops suffer with several virus and virus-like disorders.

Diseases of Apple Mosaic. This disease is widely distributed in commercial apple orchards in India. The main symptoms are various types of mottling on the leaves of affected trees. Initially, small chlorotic flecks appear on the leaf which coalesce and form bigger .bright yellow areas (Fig . .1). Sometimes, the chlorosis is restricted along veins giving vein-banding effect. The mosaic symptoms are so conspicuous that the affected trees can be distinguished easily. The causal virus in India is not transmissible by mechanical inoculations and no vector is known. The virus is easily transmissible by grafting and also through natural root contacts of healthy and diseased trees in the orchard (Hunter el aI., 1958; Dhingra, 1972b). The virus also infects the following genera: Malus, Pyrus, Prunus, Sorbus, Cydonia, Crataegus, Chaenomeies and Fragaria (posnette, 1963). The virus-causing mosaic disease in apple is spherical and can be detected in crude extract of infected petals by serological method of latex flocculation (Sequeira, 1967; Sequeira and Lister, 1969). In India, apple varieties 'Lord Lamboume', 'Jonathan' and 'Golden Delicious' are used as indicator hosts for the detection of different strains of apple mosaic virus. Three strains, i.e., mild, intermediate and severe (Fig. 1), have been well established in India (Bhargava and Bist, 1957b). The mild strain shows only a few chlorotic flecks on inoculated indicator plants, the intermediate strain exhibits vein-banding effect and the severe one causes a very severe mOwing vein clearing due to psorosis-A infection.

16b

Fig. 19. Infectious variegation symptoms on lemon leaves.

Fig. 181>. Kinnow leaves showing ring-spot due to psorosis infection. .

24

VIRUS AND MYCOPLASMA DISEASES OF FRUIT CROPS IN INDIA

Psorosis. The name 'psorosis' was coined by Swingle and Webber (1896) for a disease now known as psorosis-A. It is also called 'scaly bark' in California. Since leprosis also causes scaly bark symptoms on citrus in Florida. psorosis-A was later named as 'California scaly bark' to avoid confusion with leprosis. Psorosis -A is one of the oldest known diseases of sweet orange among psorosis disease family (Fawcett and Lee, 1926; Fawcett and Clotz, 1938, 1939). Several diseases like psorosis-A, concave gum, blind pocket, crinkly leaf, infectious variegation, satsuma dwarf and dweet monle have been put under this group and their relationship has been well described (Reuther et at., 1968). Among these, crinkly leaf and infectious variegation diseases have been well established in India (Ahlawat and Sardar, 1976; Yora et al .• 1977). However, typical psorosis symptoms were observed in Maharashtra (Nagpal. 1959 a,b), butso far there was no experimental evidence of its presence in rndia till it has been recently established by transmission experiments as a disease of sweet orange (Ahlawat, 1989). Psorosis-A. The disease shows both bark and leaf symptoms. The leaf symptoms mostly depend on weather conditions and appear on very young leaves for a short duration of 10-15 days and then disappear. The symptoms greatly vary from tree to tree and even in different species and varieties of citrus. The most characteristic symptoms developed are small elongated light-coloured areas in the region of small vein lets of the young leaves, resulting in vein-clearing or flecking on the leaves (Fig. J8a). The symptoms can easily be seen when the leaf is shaded from direct sun and viewed against the light of the sky. Sometimes only a ftlw leaves show the symptoms but often majority of leaves show vein-Clearing symptoms. In advanced stages of the disease, mature leaves and fruits also show the symptoms as circular spots or rings (Fig.18b). The most diagnostic symptoms ofpsorosis-A in the field are the development of bark lesions. These lesions develop after 6-12 years of infection (Plate 4), and is therefore difficult to identify the disease at earlier stages without indexing or other reliable" detection techniques. The lesions first appear as very small pimply eruptions, followed by scaling of bark. As these lesions enlarge, gum is exuded from the affected areas. Theold bark is ruptured and the new one comes out within the lesion area which is usually impregnated with gum. As the scaling advances, . the deeper layers of the bark and even the wood become visibly affected with gum deposits even though still alive. For some years, gummy deposits are restricted between bark and growth layers of wood. Later, the wood dies and becomes brown toreddish brown, which can bcsccn in an irregular fashion in the wood of affected trees. The affected portion of the tree then deteriorates rapidly because of the blockage of the vessels by gum and only a few small yellow leaves remain on the affected trees. The anatomy of such trees has been described by Chapman (1969). Citrus species like C. sinensis. C. paradisi and C. re/icuta/a are highly susceptible to psorosis-A, which develops both leaf and bark symptoms. Sour orange and lemon. however, remain free of bark lesions. Sweet orange cv. 'Mosambi' is good indicator host for psorosis-A in India. The strain prevalent in India does not produce bark lesions. The disease is transmissible only by grafts, but in Argentina psorosis appears to be spreading by some unknown vector (Childs, 1968). Its transmission has been suspected by natural root graft. The etiological agent of th6 disease is not known, but a capillo virus has been isolated from glasshouse inoculated sweet orange plants and also field affected 'Malta' and 'Kinnow'trees showing ring-spot

VIRUS DISEA3ES OF TROPICAL AND SUB-TROPICAL FRUITS

27

gum may exudein the centre or around the margins of the depression. With the advancement of the c,lisease some of the xylem vessels in the vicinity of the concavities become plugged with gum but not so severely as in the case of ' psorosis-A. Sweet orange and mandarin usually show these concavities when infected by this virus. In the cross-section of the wood, alternate layers Of normal wood and of wood filled with gum may be seen. The disease appears to be present in India (Mali, 1979; Mali and Chaudhuri, 1979).

Crinkly leaf. This disease is mostly found on lemon trees and is r~ported from India (Ahlawat and Sardar, 1976). Warping and pocketing due to irregul~rities of growth in different parts of the leaf blades are the common observable symptoms of the disease in the field. These symptoms vary from branch to branch. Affected trees show an upright restricted type of growth. The disease in India appears to be the same as has been reported from Australia (Fraser, 1961). Eureka lemon is selected as an indicator host for crinkly leaf virus. Yo"ung lemon seedlings develop numerous pinpoint or necrotic spots on newly developing leaves after 2-3 months of inoculation. These leaves becom,e crinkled as soon as they matu_re. As the plant grows the number of lesions decreases but their size increases and ultimately only deformed leaves can be seen. This disease is caused by an I1arvirus. Infectious variegation. This disease is mostly associated with crinkly leaf but trees having single infection have also been observed. Leaves on the affected trees show yellow or white areas on green background (Fig. 19). In some leaves, the chlorotic area are restricted to one side of the leaf but in others the whole leaf can show chlorotic areas without any definite arrangement. Affected trees are less vig - orous in growth and bear a few fruits. Psorosis-like leaf pattern is common on young leaves. The disease is reported from India (Yora et al., 1977). Sour orange and sweet orange are good indicator hosts for the detection of infectious variegation. The disease is known to be mechanically transmitted from citrus to citrus and herbaceous host (Bove and Vogel, 1961; Raychaudhuri et al., 1977). It is also caused by I1arvirus. . Satsuma dwarf. The disease is of economic importance in Japanese citrus (Yamada and Sawamura, 1952). The affected trees are stunted in growth and develop multiple stem with short internodes resulting in a bushy appearance. On affected shoots leaves are comparatively small and curled upwards into a spoon shape, but the most characteristic symptom is boat-shaped leaves. The symptom may first appear on one branch of the affected tree but it covers the whole tree in due course of time. The disease is transmitted by grafts and by mechanical inoculations on several herbaceous hosts (Tanaka and Kishi, 1963; Kishi and Tanaka. 1964; Tanaka et al., 1965). The causal virus has spherical particles of 26 nm diameter. A disease with similar symptoms, termed as leathery leaf, is commonly found in Darjeeling and Sikkim hills on mandarins (Ahlawat, 1975). It is often associated with decline of the trees (Ahlawat et al., 1979). Affected trees develop thick and spoon-shaped leaves with comparatively light in colour. Affected trees are stunted and bear only a few fruits. Apical buds are killed resulting in suppression of normal growth. Inoculated mosambi seedlings show psorosis-likc leaf flecking in young growth flushes followed by thiCkening of leaves. Such leaves remai n on the plant for a few weeks and then falloff. The disease is transmissible by graft and

VlRUS AND MYCOPLASMA DISEASES OF FRUIT CROPS IN INDIA

28

~ 20

Fig. 20. Gillis or tumors on a rough lemon shoot.

.. 21

Fig. 21. Cross-section of Cirrus decumana fruits. Right ; Albedo gumming due to impictratura virus, Left: Healthy fruit's section.

22

.

.

Fig. 22, Kagzi lime leaves showing symptoms of yellow mid-vein virus possibly a sl rain of ye.llow nct-\'c;n.

VIRUS DISEASES OF TROPICAL AND SUB-TROPICAL FRUITS

29

sap inoculation to Petunia sp. and white sesame. The vector is an aphid, Aphis gossypii. The authors are of the opinion that this disease is similar to satsuma dwarf on the basis of symptomatology and mechanical transmission to common herbaceous hosts.

Dweet mottle. The disease has been included in the psorosis family because it shows some patterns caused by psorosis or concave gum viruses when certain selections of Cleopatra Mandarin were indexed on Dweet Tangor (Childs, 1968). Affected mandarin trees do not show the symptoms but twig dieback and restricted new growth are the common symptoms. Affected trees produce only small fruits. Since dweet mottle virus do not protect sweet oranges against psorosis virus~s, it is considered to be distinct from these maladies. It is of minor economic importance. Vein enation and woody gaD tumors. In California, Wallace (1953,1959,1960) described an aphid-borne (Myzus Ilersicae) citrus vein enation disease. He also demonstrated that woody gall or tumor is caused by vein enation, virus. In South Africa, McClean (1954) reported that this disease i~ transmitted by Toxoplera eilricidus, but Laird and Weathers (1961) obtained transmission by Aphis gossypii. This disorder is of common occurrence in rough lemon and Rangpur lime. The symptoms that give the disease its name are the small enations or galls on the under surface of the leaves with corresponding depressions on the upper surface of the leaves. The galls are also found on stem and branches of the affected tree (Fig. 20). However, vein enations on the leaves are rarely seen in orchard trees. The anatomy and cytology of the so-called galls have been described by Hooper and Schneider (1969). In India, galls are found on Rangpur lime in Darjeeling hills and on Kagzi lime in Kota region of Rajasthan. The disease is transmitted from Kagzi lime to Kagzi lime (Ahlawat et al., 1984). The economic importance of the disease has not yet been determined. To establish tumor disease as a viral disorder, it must be borne in mind that the galls are also caused by a fungus on Kagzi lime (Prasad and B hatnagar, 1961). Cachexia or xyloporosis. The existence ofxyloporosis viroid in India has not been proved, though Nagpal (1959a) and Chohan and Knorr (1970) have reported its symptoms. Cachexia is a bud transmissible disease which attacks stem, bark and wood of several citrus species and varieties (Childs, 1950, 1952, 1968). Reichert and Perlberger (1934) first· described the disease on sweet lime (CilUS limettioides Tan.) in Palestine and gave the name xyloporosis. Affected trees of sweet lime rootstock having a top of sweet orange decline gradually and become unproductive within a few years. Childs (1950, 1952) described a disease similar to xyloporosis on orlando tangelo (C. retieulata X C. paradisi) and named it cachexia. The initial symptoms in sweet lime appear as pitting and the outer face of the wood shows corresponding pegs on the cam bial surface of the bark. The base of the pits and the points of the pegs are usually brown. Initial pitting develops at the point of bud-union generally after a year of inoculation. In orlando tangelo, which is used as indicator for this disease, gum deposits can be seen in the phloem region prior to the formation of pits and pegs. In advanced stages the pits are numerous and lie so near to each other that the wood

30

VIRUS AND MYCOPLASMA DISEASES OF FRUIT CROPS IN INDI A

Fig. 23. Glasshouse-inoculated lemon showing geotropic habit due \0 citrus rubbery wood infecLion. Healthy on right.

Fig. 24a. Mycoplasma-like organisms in ultra-thin sections from rubberywood-infected lemon tissue (part of the infected cell).

Fig. 24b. MLO-infected cell in ultra-thin section.

24 b

VIRUS DISEASES OF TROPICAL AND SUB-TROPICAL FRUITS

31

gives an impression Of a sieve. In advanced stages of infection, the tree appears yellow with small-sized leaves. They bloom heavily and set about normal fruit crop. Similar symptoms were also obse);ved in Parson's special mandarin which is used as an indicator. Impietratura. This disease is believed to be caused by a graft-transmissibie virus. It is reported as a serious disorder of citrus in Mediterranean region (Ruggieri, 1960, 1961, 1965), and has also been reported from India (Ahlawat et al .. 1984; Bhagabati et ai., 1986). The fruits on affected trees are small, pear shaped and hard and when such fruits are cut brown gum deposits can be seen in fruit albedo (Fig.21). On severely affected fruits brownish spots, which are sometimes depressed or may appear as bumps are the common symptoms. Gum pockets are found beneath these spots. Gum is also found in the vessels of the stem or branches on which such fruits develop. The authors observed spots similar to those of fruits on the branches of affected Citrus dec umana tree at Kalimpong. The wood below these spots shows gum deposits. Therefore these symptoms are considered to be diagnostic symptoms in young trees in the absence of fruits. Most of the affected fruits fall off during the summer and only a few mature. Similar symptoms are caused by boron deficiency but it can be ruled out if the disease is transmissible. Psorosis-like leaf pattern on field-infected grapefruit trees and also in Citrus dec umana have been observed by the authors. During transmission studies twig symptoms are observed after two years of inoculation and when such trees develop fruits similar symptoms are noticed on them. This suggest that probably the leaf and twig symptoms are the characteristics of the disease. Leaf-curl. Leaf-curl disease was originally described from Brazil (Salibe, 1959, 1965) on Pera orange. Affected trees though bloom heavily yet set only a few fruits which remain smaller in size. Shoots become weak and can easily break under slight pressure. Some gum is present in the xylem vessels. Curling and distortion of the leaves similar to the one caused by heavy infestation of aphids are the major foliar symptoms. The disease is graft transmissible and no vector is known. The virus can infect lemons, sweet orange, mandarin, grapefruits, citron, Mexican lime and sweet lime. A similar disease is reported from Maharashtra. Mali et al.(1976) observed the incidence of the disease on various citrus species. This has not yet been recorded from other parts of the country. Stubborn. In California, Waite observed that the growth of the scion bud was slow on some'Washington Navel' trees which were top worked. The new top developed also showed the same characteristic exhibited by the original trees. He described this growth as 'stubborn' (Reuther et al.,1978), and thus the same name had been retained by later workers. A little-leaf disease described from Israel and a disease locally named as 'safargali' from Egypt appears to be similar to stubborn disease. However, this disease has not yet been reported from Asian countries but the authors observed stubborn type symptoms in Akola and Tirupati regions in India. Since this is a destructive disorder of citrus, a detailed description has been given below. ' . • Stubborn disease is sometimes difficult to diagnose in the field because the symptoms are similar to other diseases like greening and non-infectious frost

32

VIRUS AND MYCOPLASMA DISEASES OF FRUIT CROPS IN INDIA

Fig. 25. Papaya leaf showing mosaic symptoms. Fig. 26. Papaya plant with leaf,curl symptom.

VIRUS DISEASES OF TROPICAL AND SUB-TROPICAL FRUITS

33

injury, heavy insect Infestation and improper nutrition. The most diagnostic symptoms are bunchy type of growth with shortened stem internodes and smaller than nonnal leaves, which usually assume an upright position (Calavan and Carpenter, 1965). The leaves on affected trees are abnormal in shape, mottled and drop excessively . Affected trees are stunted and often flattened across the top. The fruits are smaller though normal and may be lopsided and com-shaped. The styler end is abnormally ttlin and retains the green colour. Another effect is blue-albudo which is sometimes visible externally but usually by cutting into the pee]. These fruit symptoms are useful in diagnosing the disease. The seeds of seeded varieties become abortive and under-developed. When fruits of the affected trees are cut the central columella can be seen as curved, which is straight in the normal healthy fruit. Stubborn disease is a bud-transmissible disease. Experimental evidence indicates that the disease may be transmitted by insect vectors in nature (Calavari et al., 1974). Lee et al. (1973) repeatedly cultured stubborn pathogen from beet leafuopper Circulifer tene/lus (Baker) collected from sweet orange seedlings. This was an evidence that beet leafuopper can acquire the stubborn pathogen naturally. Scaphytopius nitridus (De Long) was also established as the vector of Spiroplasma citri (Kaloostian et al., 1975). In addition to C. tenellus and S. nitridus atleast II Homopterous species are demonstrated to be the vectors of Spiropiasma citri by micro-injection, membrane feeding or direct feeding on source plants. Neoaliturus haemalOceps is the main vector of stubborn in Mediterranean and near-eastern areas (Fos et al., 1986). Fawcett et al.(1944) and Fawcett (1946) considered the causal agent of stubborn as a virus. But in Egypt, Nour-Eldin (1967) suggested the causal agent as a chytrid-like organism cultured on potato dextrose agar. Later mycoplasmalike structures were obtained in ultra-thin sections of diseased tissues (Igwegbe, 1970; Igwegbe and Calavan, 1970; Lafleche and Bove, 1970). These structures were found in sieve-tubes of stubborn-affected plants but not in healthy plants. Saglio et al. (1971) from France and Fudl-Allah et al. (1971) from California cultured the organism independently (plate 5) and later its pathogenicity was proved. Saglio et al. (1973) characterized the organism and proposed the name Spirop/asma cirri for stubborn pathogen. In India, Spirop/asma species have not yet been found. Citrus yellow vein. This disease was reported from California on Kumquat (C. aurantifolia x Fortunella japonica) (Weathers. 1957). Citrus yellow vein shows synergistic reactions with several other citrus viruses (Weathers, 1960, 1961) and hence is one of the interesting citrus diseases. The symptoms on West Indian lime appear as yellowing of the main veins which appear swollen(Fig.22). The yellowing may extend to petiole and young twigs up to several centimetres. This discololiration sometimes is restricted to half of the leaf but usually both sides are affected. The disease is transmissible only by grafting and the causal virus infects several Rutaceous hosts, varieties and hybrids. Severe symptoms were observed on Florida rough lemon, calamondin, Rangpur lime, West Indian lime and Kumquat, whereas citrange, grapefruit, lemon, sour orange, sweet orange and tangelo showed I:elative]y mild symptoms, which sometimes disappear. Trifoliate orange is reported to be immune. A similar disease has been reported from India and is called as yellow mid-vein (Sharma and Pandey, 1983), or yellow corky vein (Reddy el ai., 1974) but its relationship with the original yellow vein disease is yet

34

VIRUS AND MYCOPLASMA DISEASES OF FRUIT CROPS IN INDIA

to be established though both the viruses develop similar symptoms on West Indian lime. Rubberywood. The disorder was originally described by Ahlawat and Chenulu (1985). The disease is quite prevalent in north-eastern regions, KOla region of Rajasthan and Nagpur region. In some orchards, incidence of the disease was up to 30%. It is more common in lemon and lime plantations. However, in Akola and Tirupati regions a disease of Nagpur oranges, locally called 'Valia', is the same as rubberywood. Similar disease was studied in Brazil but considered to be a reaction of exocortis (Ary Salibe, personal communication). Affected trees are characterized with the development of thin and linear shoots which bend towards the ground owing to unusual flexibility or elasticity (plate 6). Such trees are stunted and bushy, and become totally unproductive. Leaves are slightly chlorotic and smaller in size. Glasshouse-inoculated plants of Kagzi lime, lemon and mandarin develop willowing habit and their branches bend to an extent that they can touch the ground (Fig.23). In subsequent years, numerous thin branches develop at right angles which first grow very fast till they attain the height of 15-23 cm and then their growth is restricted. Usually there is no leaf fall of lemon and mandarin seedHngs in the glasshouse, but rubberywood affected plants show heavy leaf fall. Severely affected glasshouse plants show dieback and the plants die after 4-5'years of infection. After the death of main shoot, numerous branches come out from the base of the plant but they are characterized with short internodes and smaller leaves giving the plant a bushy appearance. Swell_ing of buds was also noted in Eureka lemon plants (Ahlawat and Chenulu, 1985). The disease is transmissible by grafting but not by aphids, Myzus persicae and Aphis gossypii and citrus psylla (Diaphorina cim). Recen t investigations (Ah lawat, 1987) on the etiology of the causal pathogen revealed the association of mycoplasma-like organism present in sieve-tubes of phloem tissues of diseased plants but absent in healthy plants (Fig.24a,b). Mosaic. A mosaic disease of citrus was reported from Japan (Ishigai and Jinno, 1958). The symptoms ofthe disease are large, diffuse chlorotic blotches and mottling on the leaves, with brown spots on the undersurface (Tanakaetal., 1971). The disease is transmissible by grafting (Tanaka and Yamada, 1972) and also by mechanical means (Tanaka and Imada, 1974). The causal virus has been purified and characterized. Spherical virus particles with 27 nm in diameter have been reported (Tanaka and Imada, 1976). From India, Murty and Reddy (1975), Dakshinamurty and Reddy (1976) and Ahlawat el al. (1985) described the mosaic disease. The disease is observed in citrus plantations in Andhra Pradesh, Assam, Arunachal Pradesh, Maharashtra, Maniimr, MaghaJaya, Rajasthan and Uttar Pradesh (Ahlawat el aJ .• 1985). The trees show symptom~ similar to greening disease or yellow spots on leaves but close inspection reveals the symptom-spread to be more uniform as against erratic spread by greening disease. In glasshouse-inoculated mosambi plants the disease appears as mild chlorosis, followed by severe yellow mosaic on the newly developed leaves. On mature leaves, chlorosis was severe and the leaves became leathery. Plants inoculated with mosaic remained stunted and less vigorous in gro..ylh. The disease is transmissible by grafts and aphids, Myzus persicae Sulz.,Aphis craccivora Koch. (Ahlawat et al .. 1985) and Toxoptera cilricidus (Dakshinamuny

VIRUS DISEASES OF llWPICAL AND SUB.TR'oPICAL FRUITS

Plate 5. Spiroplasma cilri causal

organl~rns

35

of citrus stubborn disease from anificial culture.

and Subbayya, 1981). It is also known to be seed transmitted. The virus infects sweet orange (cv. 'Mosambi', 'S~tgudi' ,:Washington Nave!'), Indian acid lime. Rangpur lime, grapefruit, mandarin, lemon, pummelo and bale fruit (Aegle marme/os Corred.). In Sikkim orange, disease symptoms are as chloro~is of the leaves with clear mosaic p~ttem, extreme reduction of the leaf lamina and wavy margin of leaves. These symptoms are considered as the diagnostic symptoms of the disease. Therefore, Sikkim orange has been recommended as differential host for mosaic and greening infections (Ahlawat el al., 1985). ., The virus has been purified and spgeri_cal particles observed. The disease appears to be different (rom that reported from Japan because the aritiserum obtained from Japan against mosaic did nOl react with Indian isolates (Ahlawal, unpublished). Recent investigation revealed the association of a bacilliform virus with a mosaic of pummelo and sweet orange.

Miscellaneous Diseases or Citrus In addition to the ones described above, there are some more citrus disorders described in India or elsewhere. These include citrus tauer-leaf (Wallace and Drake, 1962), citrange stunt (Wallace and Drake, 1968), citrus ring-spot (Wallace and Drake, 1968), cirstacortis (Vogel and Sove, 1964), multiple sprouting (Searle, 1969; Ahlawat and Chenulu, 1985), bud-union crease (Grant el al .. 1957), blastomania (Mali et al., 1975). yellow corky vein (Reddy el al:,.1974). C'itrus leathery

.

.

36

vrn.US AND MYCOPLASMA DISEASES OF FRUIT CROPS IN INDrA

Plate 6. Symptoms of rubbery wood on a mandarin tree.

leaf (Ahlawat, 1975~ Ahlawat et al., 1979) and witches' broom of limes (Bove el ai. , 1986) . . Some more diseases with virus-like symptoms have been observed in citrus but theircause is unknown. The importam ones are rumpJe oflemons (Knorrel al., 1963), wood pockeL or lignocortis (Calavan, 1957), tarocco pit (Russo and Klotz,

VIRUS DISEASES OF lROPICAL AND SUB-lROPICAL FRUITS

37

1963) and lemon sieve-tube necrosis (Schneider, 1960). Virus Diseases of Papaya \ Papaya is grown almost throughout India. Several high-yielding and dwarf varieties like 'Pusa Nanha' are becoming popular and the production of this highly nutritive fruit has gone up: In India, the area under papaya cultivation is about 10,000 ha, but the virus diseases are the major constraints in the successful cultivation of this crop. Papaya is reported to be the host of several virus diseases likeleaf-curl (Nariani, 1956), mosaic (Capoor and Varma, 1958),leafreduction (Singh, 1969) and ring-spot (Khurana, 1974; Yemewar and Mali, 1980). In India, mosaic, leaf-curl-and ring-spot diseases are causing heavy losses to papaya plantations. They may affect the plants individually or in combination. Mosaic. This disease is widely prevalent in papaya plantations and is recorded from Andhra Pradesh, Bihar~ Maharashtra, Madhya Pradesh, Uttar Pradesh and West Bengal. The incidence of the disease is sometimes up to 100% in some plantations. The disease produces typical mosaic symptoms showing chlorosis of the leaf lamina with dark green blisters. The lamina is reduced and becomes malformed (Fig.25). The stem, petiole and even fruits develop elongated water-soaked areas showing concentric or circular rings or lesions. After the symptoms are fully developed the plants show decline and marked reduction in growth is observed. As the disease advances, older leaves fall down and a small tuft of younger leaves is left at the top which are also malformed and have typical mosaic symptoms. The disease is transmissible by mechanical inoculation and by grafting. Natural spread takes place through aphids, Myzus persicae, Aphis malvae. A. gossypii, A. medicaginis and Macrosiphum son chi in a non-persistent way. The disease is not soil borne (Capoor and Varma, 1958). The following plant species were artificially infected with papaya mosaic virus: Lagenaria siceraria (Molina) Snndl., Trichosanthes anguina L., Cucurbila maxima Duch., C. pepo L., C. peyo var. medullosa. Citrullus vulgaris Schrad, C.fistulosus. Cucumis sativus L., C. melo L. and Luffa aculangula (L.) Roxb. The virus has a thermal inacti vation point between 53° and 55° C, and dilution end-point between to· 3 and 1(J". The virus survives aging in vitro at room temperature for only 26 hours. Carica cauliflora, a wild papaya, is found immune to mosaic infec tion (Capo or and Varma, 1961). WeekI y sprays with 10% groundn utoil help in preventing spread of the dis~ase in the orchard (Bhargava and Paul Khurana, 1969). ,

Leaf-cu rl. The disease was first reported by Thomas from Madras. Later, this disease was found in Delhi and also in Bihar. It has been studied in detail at IARI, New Delhi (Nariani, 1956). The disease is characterized by severe curling, crinkling and distortion of the leaves accompanied by vein clearing and reduction of leaf lamina (Fig. 26). The leaf margins are rolled downward and inward in the form of inverted cap. The veins get thickeneCl and turn dark green. The leaves become leathery and brittle, and petioles are twisted .. Affected plants bear only a few flowers and fruits. In advanced stages, defoliation takes place and growth is stunted. In nature, the disease spreads by whitefly, Bemisia tabaci. 'The disease is not mechanically

38

VIRUS AND MYCOPI:ASMA DISEASES OF FRUIT CROPS IN INDIA

27

"

FIg. 27. Banana plant showing bunchy

lOp

symptoms . Healthy on left.

Fig. 28. Banana leaf with infectious variegation symptoms.

"28'"

VIRUS DISEASES OF TROPICAL AND SUB·TROPICAL FRUITS

39

transmissible. The virus has a wide host range and infects sunnhemp, chilJi, petunia, zinnia, Datura stramonium and several other weeds and ornamental plants. The virus is experimentally transmitted to tomato and tobacco where it produces the symptoms of leaf-curl disease. A gemini virus is apparently associated with the disease. Ring-spot. The disease has been reported from Marathwada region of Maharashtra (Yemewar and Mali, 1980). The symptoms appear as mosaic mottling,leaf distortion and redu(::tion in leaflamina, streaks on Siem and petiole, rings and spots on fruits, and stunting of the plants. The disease incidence during 1977-78 is reported to be about 79%. , The virus is mechanically transmissible from papaya to papaya, Chenopodium amaranticolor, C. quinoa, Benincasa hispida, Cucumis melo, C. sativus, Cucurbita moschata, C. pepo cv. 'Patipan', and Luffa cylindrica. The insect vector is Aphis gossypii which transmits the virus in a non-persistent manner. The virus is inactivated at 60°-65°C and is viable up to 10 hours at 27°-30~C. It loses its infectivity at a dilution of 10-3 in papaya leaf sap. The virus has been reported to be a member of POly virus group. Virus Diseases of Grapevine The area under grapevine cultivation in India is about 0.0114 million hectare with a production of about 0.22 million tonnes. Grapevine is reported as a natural host of several viruses affecting other crops. The viruses are arabis mosaic, peach rosette mosaic, tobacco mosaic, apple mosaic, tomato black-ring, tomato bushy stunt and tomato ring-spot. In addition, several other virus/MLO diseases were recorded from grapevine such as asteroid mosiac (Hewitt and Goheen, 1959; Hewitt. 1968), grapevine corky bark-a mycoplasma disease (Hewitt, 1968). enation disease (Refatti, 1966), fan-leaf (Cory and Hewitt, 1968; Cadman et al., 1960), leaf-roll (Hewitt, 1968), vein clearing (Goheen and Hewitt, 1962) and Pierce's disease (Hewitt, 1939) now kno.wn to be caused by a bacterium (Mollenhaver and Hopkins, 1974). Fortunately, no such disorders have been found in Indian grapevines. Fan-leaf is a very important and widely distributed disease in grape-producing countries and is described below. Fan-leaf. The affected vines get stunted with short internodes which develop in a zigzag fashion. Affected nodes sometimes develop 2-3 buds. The leaves on affected vines are smaller than the normal with widened petiolar sinuses. Because of this and reduction of leaf area between the main vein, the leaf lamina appears like a half-closed fan, leaf incision becomes deeper and leaf margin becomes irregularly serrate. Most of the affected leaves show some degree of vein clearing. Fruit setting is poor on affected vines. The virus is mechanically transmissible to Gomphrena globosa, Chenopodium amaran~icolor, Nicotiana tabacum cv. 'White Burely', Phaseolus vulgaris cv. 'Prince' and Cucumis sativus (Cadman et al., 1960). Fan-leaf virus was isolated from the pollen of grapevine and herbaceous hosts and also in seed of herbaceous test plants (Cory and Hewitt, 1968; Dias, 1963). The vectors are nematodes, Xiphinema index (Hewitt et al., 1958) and, X. italiae (Cohn et al., 1970). The virus has been purified and its properties studied by Cadman et al. (1960) and Harrison and Nixon (1960). The virus particles are isometric between 25 and 30 nm diameter (Dias, 1963). ' .

40

VIRUS AND MYCOPLASMA DISEASES OF FRUIT CROPS IN INDIA

Little-leaf. Singh et al. (1975) observed this disease in 'Merlot Noir' variety of grapevine in Bangalore. The leaves on affected vines become extremely small and develop light-yellow colour. Internodes and stem are reduced to a great extent and develop in zigzag fashion. Axillary buds proliferate. No flower and fruit develop on affected vines. Roots also become stunted and a few weak rootlets develop. The disease is transmissible by grafting or budding. and symptoms on grafted plants may appear within 40-45 days. A temporary remission of disease symptoms was obtained by heat therapy (45 0 and 50°C) and also when bud woods . were treated with 1,000 ppm oxytetracycline hydrochloride. The disease is presumed to be caused by mycoplasma-like organisms. Virus Diseases of Banana Banana is a very important and economically profitable crop in India and has a very high export potential. The crop covers about 42,900 ha and is grown throughout India. Banana suffers from some devastating virus diseases which are responsible for heavy losses to the crop. Certain highly susceptible varieties are on the verge of extinction. Bunchy top and infectious chlorosis are the two major disorders of banana plantations. Bunchy top. The disease is believed to have been introduced in India through a cyclone in 1940. It has spread quickly to most of the banana-producing states. Its quick spread is because of strict vegetative propagation of the crop and also availability of insect vector (s). The most characteristic symptoms of the disease are shortening of the leaves both in length and breadth and are bunched at the top of the pseudostem resulting in rosette or bunchy appearance (Fig.27)'. Affected plants remain stunted and leaf stalk is extremely reduced. The margin of the leaves becomes wavy and then roll upward. Because of the reduced leaf stalk, the leaves develop in an upright and erect position. Against light, the young leaves invariably show dark green streaks or dashes along the middle or secondary veins. The plants do not develop any fruits when infected at a young stage. However, a few bunches of small stunted fruits may emerge from plants infected at later stages. Because of the leaf congestion and constriction at the apex of the stem, fruit bunches cannot emerge easily. The root system is also affected and shows some decay. The virus is not mechanically transmissible. It is transmitted by the aphid vector Pentalonia nigronervosa Cock. in a semi-persistent way (Magee, 1940). The primary spread of the virus is through infected suckers. Most of the banana varieties are susceptible to bunchy top infection but well-known varieties like 'Hari Sal' and 'Lal Velchi' are highly susceptible. The virus also infects Musa cavenaishii, M. sapienturn, M. fehi and M. textilis. Outside family Musaceae, the virus infects Colocasia esculenla (L.) Schott. (Ram and Summanwar, 1984), which is grown as inter-crop among banana plantations in Deccan Plateau of Maharashtra. Hence it serves as a reservoir of the virus and also the host of its vector P. nigronervosa(Mehtaet al., 1964; Maratheetal., 1982). The morphology of the causal viruS" has not yet been established in India. A colour test with 1% of 2,3,5-triphcnyl tetrazolium chloride is used for the detection of bunchy top in banana suckers. It is of great value.in certification programmes (Summanwar'and Marathe, 1982). Mosaic/infectious chlorosis. This disease appears in endemiC form in certain parts of Maharashtra. It is serious problem in the Jalgaon-Dhule region of the State. The disease was first reported from this state and was endemic in Khandesh

VIRUS DISEASES OF lROPICAL AND SUB-lROPICAL FRUITS

41

district (Capoor and Varma, 1968). Leaves on severely affected plants show broad chlorotic or yellow patches which cover most of the leaf portion (Fig.28). Initially, chlorotic spots develop on leaves without any definite arrangement. Affected plants are comparatively stunted and seldom produce a fruit bunch. The fruits developed on affected plants have no commercial value. The disease is mechanically transmissible from banana to cucumber but not from cucumber to banana back, The insect vector is the melon aphid, Aphis gossypii Glover. Forty-four cultivated_banana varieties including 'Basrai' and 'Velchi' are susceptible to mosaic infection. Musa balbisiana, M. chillicarpa, M. coccinia and M. acuminata were found immune (Capoor and Varma, 1968). Banana diseases perpetuate'in the field by way of multiplication of diseased suckers and also by aphid vector. Therefore eradication of diseased suckers and use of virus-free planting material alone can help to. reduce the menace of the disease to a great extent. '

Pineapple Wilt A wilt of pineapple originally reported by Carter (I933) was also reported from India (Singh and Sastry, 1974). As the name indicates, wilting of affected plants is the most important symptom of the disease. Different degrees of anthocynin and curling of leaves have been reported depending upon the season. The disease is transmitted by a mealy-bug (Dysmicoccus brevipes). Disease was eliminated from affected suckers by hot water and heat treatment at 50"C for 3 hours. This has been considered the same disease as described by Carter. REFERENCES Ahlawat, Y.S. 1975. Leathery leaf-a new virus disease isolated from greening-affected mandarin tree. Indian Phylopalh. 28: ) 46 (Abstr). Ahlawat, Y.S. 1987. 'Association of mycoplasma-like organisms with rubbery wood disease of citrus'. 3rd Regional Workshop on Plant Mycoplasma, INSA, New Delhi, p. 12. Ahlawat, Y.S. 1989. Psorosis-A disease of citrus in India. India" Phytopath. 42 : 21-25. Ahlawat, Y.S. and Chenulu, V. V. 1985. Rubbery wood and multiple sprouting-two newly discovered diseases of citrus (Abstr.). 37th Annual Meeting IPS, Lucknow. India" Phytopath. 38 : 625. Ahlawat, Y.S. and Sardar, K.K. 1976.Lemon crinkly leaf virus in India. India" J. Hort. 33 : 168-171. Ahlawat, Y.S., Nariani, T.K. and Sardar, K.K. 1979. Leathery leaf: A new virus disease of citrus.lndia1l Phytopath. 32: 198-201. Ahlawat, Y.S" Chenulu, V.V., Chakraborty, N.K. and Viswanath, S.M. 1984. Occurrence of impeitratura disease of citrus in India. CUTr. Sci. 53 : 384-385. Ahlawat, Y.S., Chenulu, V.V., Viswanath, S.M. and Pandey, P.K. 1985. Studies on a mosaic disease of citrus in India. CUTr. Sci. 54 : 873-874. Balaraman, K. and Ramakrishnan, K. 1977. Studies on strains and strains reaction in citrus tristeza virus. Tech. Ser. Bull. 19, U A.S., Ba1lgalore. Bar-Joseph, M. and Loebenstein, G.1970. Leaf Ilecking on indicator seedlings associated with citrus impeitratura in Israel. A possible indexing method. Pl. Dis. Reptr. 54: 643-645. Benton, R.J., Bowman, F.T., Fraser, L. and Kebby, R.G. 1949. Stunting and scaly bark of citrus associated with Poncirus trifoliata rootstock. Gaz. N.S.Wates 61 : 521-526, 577-82,641-45,654. Bhagabati, K.N., Thakur, B.C. and Ahlawat, Y.S. 1986. Occurrence of impeitratura disease of citrus in north-eastem India.lndia1l Phylopath. 39 : 110-111. Bhargava, K.S. and Paul Khurana, S.M. 1969. Papaya mosaic controlled by oil spray. Phytopalh. Z. 64: 338-343. Biuers, W.P. 1952. Exocortis on trifoliate. Citrus Leaves 32: 14-16,34. Bove,J.M., Gamier, M., Mjeni, A.A. and Khayrallah, A.1986. 'Witches' broom disease of small fruited acid lime trees in Oman~ First MLO Disease of Citrus. 10th Conference of IOCV (Abstr.), p.96.

42

VIRUS AND MYCOPLASMA DISEASES OFFRVlT CROPS IN INDIA

Bove, J.M. and Vogel, R. 1961. L et at sanitaire des agrumes en corse. Fruits 16: 137-]42. Brown, W.R. 1920. The orange: A trial of stocks at Peshawar. Pusa agrie. Res. lnst. Bull. 93 : 7. Cadman, C.H., Diu, H.F. and Harrison, B.D. 1960. Sap transmissible viruses associated with diseases of grapevine in Europe and North America. Nature, Lond. 187 : 577. Calavan, E.C. 1957. Wood pocket disease of lemons and seedless limes. II. Perpetuations and transmission nudies. Calif. Citrograph. 42 : 300-04. Calavan, E.C. and Carpenter, lB. 1965. Stubborn ~sease of citrus trees retards growth, impairs quality and decreases yield. Calif. Cilrograph. SO : 86-87,96,98-99. Calavan, E.C., Harjung, M.K., Fudballah, A.E.S.A. and Bowyer, J.W. 1974. 'Natural incidence of stubborn in field grown citrus seedlings and buddings', (Eds) L.G. Weather and M.Cooen. Proceedings of 6th Conference of International Organization on Citrus Virology. pp. 16·19. University of California, Division of Agriwhural Science, Richmond. Capoor, S.P. 1961. Kagzi lime: An indicator plant of the citrus decline virus in India. I ndian P hytopath. 14: 109-112Capoor, S.P. 1963. Decline of citrus trees in India. Bull. Nat.lnst. Sci. India 24: 48·64. Capoor, S.P. 1965. Presence of seedling yellows complex in the citrus of South India. Proc. 3rd Conf. Intern. Organ. Citrus Virol. pp. 3()"35. Univ. Florida Press, Gainesville. Capoor, S.P. ] 975. Role of the tristeza virus in citrus dieback complex. Indian J.Ho,.t. 32 : 1-6. Capoor, S.P. and Rao, D.G. 1967. 'Tristeza virus infection of cilJUS in India'. Proceedings of International Symposium on SulHropical and Tropical Horticulture. Horticulture Society of India, Bangalore, pp. 123-736. Capoor, S,P. and Varma, P.M. 1958. A mosaic disease of papaya in Bombay. Indian J. agrie. Sci. 18 : 225-233. Capoor, S.P. and Varma, P.M. 1961. Immunity of papaya mosaic virus in the genus Carica. Indian Phytopath. 14 : 96-97. Capoor, S.P. and Varma, P.M. 1968. Investigations on a mosaic disease of banana in the Deccan. IndiaI'! Phytopath. 21 : 135. Capoor, S.P., Rao, D.G. and Vishwanath, S.M. 1967. Diaphorina citri Kuway, a vector of the greening disease of citrus in India. Indian J. ag"c. Sci. 37 : 572-576. Carter, W. 1933. The pineapple mealyling. Pseudoc()(;cus breuipes and wilt of pineapple. Phytopathology, 23 : 207-242. Chapman, H.D. (Ed.) 1969. Proceedings of 1st International Symposium. Vol. 3, pp. 1105-1833, Riverside, University of California. Childs, J.F.L. 1950. The cachexia disease of orJant4o tangelo. PI. Dis. Reptr 34: 295-298. Childs,l.F.L. 1952. CacheXIa disease, its bud transmission and relation to xyloporosis and tristeZB. Phytopathology, 42 : 265-268. Childs, J.F.L. (Ed.). 1968. Proceedings of 4th Conference of International Organization of Citrus Virologists. University of Florida Press, Gainesville, 404 pp. Chohan, 1.S. and Knorr, L.C. 1970. Diseases. In Citrus Decline in India. A Joint Publication of Punjab Agricultural University and Ohio State University. U.S. Agency for International Development, pp.79-97. Cohn, E., Tanne, E. and N itzanim, E.E. 1970.Xiphinema italiae, anew vector of grapevine fan-leafvirus. Phytopathology, 60 : 181-182. Cory,L,and Hewitt, W.B. 1968. Some grapevine viruses in pollen and seeds. Phytopathology, 58: 13161320. Dakshinamuny, V. and Reddy, G.S. 1975. Mosaic-a transmissible disorder of sweet oranges. India1l Phytopalh. 28: 398-399. Dakshinamuny, V. and Reddy, G.S. 1976. A non-citrus host for citrus mosaic virus. Curro Sci. 4S : 352. Dakshinarmuny, V. and Subbayya, J. 1981. 'Studies on transmission of citrus mosiac-a new disease of Citrus sinensis in Andhra Pradesh (Abstr.)'. 3rd International Symposium on Plant Pathology at New Delhi. 14-18 December, 1981. Dias, }I.F. 1963. HOSI range and properties of grapevine fan-leaf'and grapevine yellow mosaic viruses. Ann. appl. Bioi. 51 : 85·95. . Dickson, R.C. and Flock, R.A. 1959. 'Insect vectors oftristeza virus'. University of California, Division of Agricultural Sciences, Berkeley, pp. 97-99.

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Fawceu. H_S. 1936. Citrus Diseases and their Conl~ol. 2nd edn., 656 pp. McGraw-Hili Book Company Int., New York. and London. Fawcett. H.S. 1946. Stubborn diseases of citrm, a virosis. Phytopathology, 36 : 615-617. Fawcett. H.S. and Klotz. LJ. 1938. Types and symptoms of psorosis and psorosis-like diseases of citrus. Phytopathology, 28 : 670. Fawcett. H.S. and Klotz, LJ. 1939. Infectious variegation of citrus. Phytopathology, 29 : 911-912. Fawceu. H.S. and Klotz, L.J. 1948. Exocortis of trifoliate orange. CitrllS Leaves, 28 : 8. F.awceu. H.S. and Lee. H.A. 1926. Citrus Disearesand /heirCOnJrol. 582 pp. McGraw-Hili & Co., New York. and London. , Fawcett, H.S., Perry, lC. and Johanston, J.C. 1944. The stubborn disease of citrus. Calif. Citrograph. 29: 146-147. Fos, A., Bove,J.M., Lallemand.J.,SaiJIard, C., Vignault, J.C., Ali, Y., Brun, P. and Vogel, R. 1986. La Cicadelle NeoalilurllS haema/oceps (Mulsant & Rey) est vecteur de Spiroplasma citr; en Medilerranee. Ann./ns. Pasteur. Microbiol. 137A ; 97-107. Fraser Lilian. 1961. 'Lemon crinkly leaf virus'. Proceedings of 2nd Conference of International Organization of Citrus Virologists. pp: 205-210. Univ. Aa. Press, Gianesville, Aorida. Fraser, L. and Levitt, B.C. 1959. Recent advances in the study of exoconis (sc;aly bud) in Australia. In CitrllS Virus Diseases. pp. 129-133. University of California, Division oi"AgricuJtural Sciences, Berkeley, California. Fraser, L., Singh,D., Capoor, SoP. and Nariani, T.K. 1966. Greening virus, the likely cause of citrus dieback in India. FA.O.PI. Prot. Bull. 14: 121-130. Fudl-Allah, A., Calavan, E.C. and Igwegbe, E.C.K. 1971. Culture of a mycoplasma-like organism associated with stubborn disease of citrus (Abstr.). Phytopathology, 61 ; 1321. Gamier, M., Daniel, N. and Bove, 1.M. 1984. 'The greening organism is a Gram-negative bacterium'. Proceedings of 9th Conference of International Organization of Citrus Virologists. pp. 115. Garnsey, S.M. 1968. Exocortis virus of citrus can be spread by contaminated tools. Citrus/lid. 49: 13-16. Garnsey, S.M. and lones, l.W. 1961. Mechanical transmission of exoconis virus with contaminated budding tools. PI. Dis. Reptr 51 ; 410-413. Goheen, A.C. and Hawilt, W.B. 1962. Grapevine vein banding virus. AmJ.£r&J. Vi/ie. 13 : 73-71. Grant, T.l., Moreira, S. and Costa, A.S.1951:0bservations on abnormal citrus rootstock reaction in Brazil. Pl. Dis. Replr 41 : 143-48. Harrison, B.D. and Nixonm. H.L. 1960. Purification and electron microscopy of three soil-borne plant viruses. Virology,'12 : 104-111. Hewitt, W.B. 1939. A transmissible disease of grapevirus. Phylopalhology, (Abm.) 29 : 10. Hewitt, W.B. and Goheen, A.C_ 1959. Asteroid mosaic of grapevines in California. PhY/opathology. (Abstr.) 49 ; 541. Hewitt, W.B. 1968. Viruses and virus diseases of the grapevine. Rev. appl. Mycol. 47: 433-55. Hewitt, W.B., Raski, OJ. and Goheen, A.C. 1958. Nematode vector of soil-borne fan-leaf virus of grapevines. Phytopathology, 48 ; 586-595. Hooper,G.R. and Schneider, H. 1969. The anatomy of tumors induced on citrus by citrus vein enation virus. Am. J .Bot. 56 : 238-247. 19wegbe, E.C.K. 19'10. Studies 011 the nature and t,a1l3mission of the causal agent of stubborn of citrus. Association of a mycoplasma-like organism with the disease. Ph. D. Thesis, Depanment of Plant Pathology, University of California, Riverside, California Igwegbe. E.C.K. and Calav an, E.C. 1970. Occurrence of mycoplasma-like bod ies in phloem of stubborn infected citrus seedlings. Phytopathology, 60 ; 1525-26. Ishigai. T. and Jinno, M. 1958. On citrus mosaic. Ann. Phytopath. Soc. Japan 23 ; 29. Kaloostian, G.H., Oldfield, G.N., Pierce, H.D., Calavan. E.C., Garanett. A.L., Rana, G.L. and Gumpf, D.l. 1915. Leafhopper may be a natural vector of citrus stubbom disease. CaliJ.Agric. 29 (2) :1415. Khurana, S.M.P. 1974. "Studies on three virus diseases of papaya in Gorakhpur, India'. Proceedings of 9th International Honiculture Congress, Warsa (Poland). 14 : 260 {Abstr.}. Kishi, K. and Tanaka. S. 1964. Studies on the indicator plants for citrus viruses', II. Mechanical transmission of the virus, causing satsuma dwarf to sesame (Sesamum illdieum).1nn. Phylopath Soc. Japan 29 :142·148. I

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VIRUS AND MYCOPLASMA DISEASES OF FRUIT CROPS IN INDIA

Kitajima, E.W. 1965. 'Election microscopical investigations on tristeza'. Proceedings of the 3rd Confer· ence of International Organization of Citrus Virologists. pp. 1-9. University of Florida Press, Gianesville, Florida. Klotz, L.I. 1961. Colour handbook of citrus diseases. University of California, Division of Agricultural Sciences, Berkeley,1S pp. KnOTT, L.C., Olsen, R.W. and Kesterson, J.W. 1963. Rumple of lemons, its effect on fresh fruits, lemonade concentrate, and pe~1 oil. Fla. Stale HOT!. Soc. Proc. 16 : 36-41. Laird, E.F. and Weathers, L.G. 1%1. Aphis gossypii. a vector of citrus vein·enation virus. Pl. Dis. Replr o

45: 811. Leafleche. D. and Bove, J.M. 1910. Structure de type mycoplasma dens les feuilles d' orangers atteints de la maladie du "greening". C.r. Acad. Sci. (Sec.D) 270: 1915-1911. ' Lee, I.M., Cania, G., Calavan, E.C. and KalooSlian, G.H. 1973. Citrus stubborn disease o'rganism cultured from beet leafhopper. Calif. Agric. 27 (11) : 14-15. Lin, K.H. 1964. A preliminary study of the resistance of yellow shoot virus and citrus bud tissue to hCllL Acta Phylopath. Sin. (Peking) 1: 61-65.• Magee. C.J.P. 1940. Transmi ssion studies of the banana bunchy top virus.!. AUSI.fnst. agric. Sci. 6 : 109110. Mali, V.R. 1919. Indelling results of mosambi, sweet orange decline on rough lemon rootstocks in Maharashtra.fndianJ. Mycol. Pl. Path. 9: 193-199. Mali, V.R. and Chaudhuri, K.G. 1919. Index.ing ~sults of citrus decline on rough lemon rootstocks. Indian Phylopath. 32 : 496-498. • Mali, V.R., Chaudhuri, K.G. and Rane. S.D. 1915. Blastomania-a new bud transmissible disorder of citrus. Curl'. Sci. 44: 621-628. Mali, V.R., Chaudhuri, K.G.and Rane, S.D. 1976. Leaf-curl virus disease of citrus in India. Sci. Cull. 42: 525-521. Marathe, T.S., Summanwar, A.S. and Ram, R.D. 1982. New additional hosts of Pentalonia nigroner. vosa. Curro Sci. 51: 435-436. McClean, A.P.D. 1954.Citrus vein enation v~rus. SAfr. J. Sci. 50: 147-151. McClean, A.P.D. and Oberholzer, P.C']. 1965. Citrus psylla, a vector of the greening disease of sweet orange. S. Afr. J.Sci. 8: 281-298. Mehta. P.R., Joshi, N.C., Rao, N.M. and Eenjhen. P.L. 1964. Bunchy top -a serious disease of banana in India. Sci. Cull. 30 : 354-363. Mollenhaver, H.H. and Hopkins, D.L. 1914. Ultrastructure study of pierces disease bacterium in grape xylem tissue. J. Bact. 119: 612-618. Nagpal, R.L. 1959a. Tristeza and other diseases of citrus found in Bombay State. Citrus Ind. 40 : 14-15. Nagpal, R.L. 1959b. Tristeza found in Bombay State. Calif. CitrogToph. 44 : 402-405. Nariani, T.K. 1956. Leafcurl of papaya. Indian Phylopalh. 9: 151-151. Nariani, T.K. and Raychaudhuri, S.P. 1910. Transmission of citrus tristeza virus by dodder, CUScUla re!eUl Roxb. Ann. Phylopath. Soc. Japan 36 (4) : 289-290. Nariani, T.K., Sahambi, H.S. and Chona, B.L. 1965. Occurrence of tristeza virus in citrus in northem India. Indian Phylopalh. 18 : 220. Nariani, T.K., Raychaudhuri, S.P. and Shanna, B.C. 1968. Exoconis in citrus in India. PIDis. Replr 52 (11) : 834. , Nariani, T .K., Raychaudhuri, S.P. and Vlswanath, S.M. 1973. Tolerance to greening disease in certain citrus species. Curro Sci. 42: 513-514. Nour-Eldin, G. 1961.A tumor-inducing agent aS$ociated with citrus trees infected with safergali (stubborn) disease in the United Afab Republic. Phytopathology. 57 : 108-113. Patil, B.P. and Warke, D.C. 1968. A note on existence ofexoconis virus in India. Curro Sci. 37 : 469-470. Prasad. N. and Bhatnagar, C.G. 1961. Sphaeropsis knots on lime (Cilrus medica var. acida Linn.) in Rajasthan. Curro Sci. 30: 110-111. Pratt, R.M. 1958. Rorida guide to citrus insects, diseasc~ and nUlritiQllal disorders in colour. Agric. Exp. Sin Gainesville, 181 pp. Ram, R.D. ~d Summanwar. A.S. 1984. Colocasia escu/enla (L.) Schott., a reservoir of bunchy top disease of banana. Curr. Sci. 53: 145-146. Raychaudhuri, S.P. 1972. 'Epiph)ClOlogy of the greening disease of citrus in India'. Final Technical

VIRUS DISEASES OF TROPICAL AND SUB-TROPICAL FRUITS

45

Progress Report (25 Aug. 1967 to 24th Aug. J972), Division of Mycology and Plant Pathology, IARI, New Deihl. \ Raychaudhun, S.P. and Ahlawat, Y.S. (Eds) 1982. Problems ojCitrus Diseases in India . Surabhi Printers and'Publishers, New Delhi. Raychaudhuri, S.P., Nariani, T.K. and Ahlawat, Y.S. 1977. Dieback of citrus in India. PTOC. Int. Soc. Citriculture 3: 914-918. I •. Reddy, G.S. and Govmda Rao, P. 1961. 'Is there tristeza in Andhra Pradesh, India'. pp. 132-135. Proceeqings of 2nd Conference of Intemaitonal. Organization of Cllrus Virologists. University of Florida Press, GaineSVIlle. " Reddy, G.S., Dakshinamurty. y. and Reddy, V.R.K. 1974. Yellow-corkyvien: Fir~'trepon of anew graft transmissible disorder of 'Sathgudi' in Andhra Pradesh. Ind,an Phytopath'. 27 : 82-84. RefauI, E. 1966. Su una possible correIazione frail Vtrus del complesso delt ani~iamento a la malattia delle enazioni nella vite. Rlv. Veg. Pakia. Ser. 2 (4): 207-217. Reichert,!. and Perlberger, 1.1934 XyloPC;rosis, the new citrus disease. Jewish Agency jar Palestine ' AgTic. Exp. Sta. (Rehovot) Bull 12: 1-150. Reuther, W., Clair Calavan, E. and Carman Glenne. 1978. The_Citrus Industry. VolA. Division of Agricultural Sciences, Univer,sily}>f California, Berkeley, California, pp; 362. Reuther, W., Calavan, E.C., Mauer, E.M. and ROlstacher, C.N. 1968. Citrus variety improvement pwgram provides wide benefits. Calif. Curograph. 53 : 205, 222-224, 226-228-,_215-278:-280. Rossetti, V. and Salibe, A.A. 1962. Prevalencia das das doenceas de virus dos citms no estado de sao paulo. Bragan!. pp. 107-121. Ruggieri, G. 1960. 'Present pOSition of citrus virus diseases in Italy'. ReportofInternational Conference on ViruS DIseases of Citrus. AClTeale, Sicily, Sept. 1959. E.P.P.O., Paris. Ruggieri, G. 1961. 'Observations and research on impietratura'. Proceedings of 2nd Conference of International Organization of Citrus Virologists. pp. 182-186. University of Florida Press, Gainesville", Florida. Ruggieri, G. 1965. 'On the impietratura of grape fruit'. Proceedings of 2nd Conference of International Organization of Citrus Virologists. pp. 179-181. University of Florida Press, Gainesville, Florida. Russo, F. and Klotz, L.J. 1963. Wrinkle raid of lemons in Sicily. Calif. CilTograph. 48: 264. Sagho, P.,Leelechc, D., Bonissol, C. and Bove:J.M. 1971. Isolement etculture invitro des mycoplasmes associes au 'stubbom' dis agrimes e\ leur observation an microscope electronique. C.r. Acad. Sci Paris (Sene D) 272 : 1387-1390. Saglio, P., Hospital, M.L., Lafleche, D., Dupont, 0., Bove, 1.M., Tully, J.G. and Freundt, E.A. 1973. Spiroplasma cilri gen. and sp. A mycoplasma-like organism associated with stubborn diseases of citrus. Intern. J. Syst. Bact. 23 : ~1-204. Salibe, A.A. 1959. Leafcurl- a transmissible virus. disease of citrus. Pl. Dis. Reptr 43: 1081-1083. Salibe, A.A. 1965. 'Susceptibility of citrus varieti,es to leafcurl virus'. Proceedings of3rd Conference of International Orgam~alion of Citrus Virologist. pp. 715-78. University of Florida Press, GaineSVille, Florida. Sanchez-Arellano, L. and Weathers, L.G. 1971. Enfermedades de los cinicos. Santiago, Chile: SA.G. Minlsteriode Agricoltur Tech. 45 ; 60. SchneIder, H. 1946. A progress reponon quick decline: Histological studies (part III). Calif. Cilrograph. 31:198-199. Schneider, H. 1947. Quick decline and tristeza similarities. Citrus Leaves 27 (8): 10-11. SchneIder, H. 1954. Anatomy of bark of bud· union, trunk and roots of quick decline affected sweet orange trees on sour orange rootstocks. Hilgardla. 22 : 267-601. Schneider, H. 1959. The anatomy of lnsleza-vlrus infected citrus. In ClIrus V,rus Diseases pp.73-84. University of California, DiVision of Agncultural SCIences, Berkeley, California. Schneider, H. 1960. Sieve·tube necrosis in nucellar lemon trees. CalijCitrograph 45: 208, 219-222. Searle, C.M. 1969. A prelIminary repon on off type trees. Mawc Citrus Estates (RhodeSia), 15 pp. Semanclk, 1.S. 1976. 'CItrus exocortls disease 1965 to 1975'. Proceedings of 7th Conference of InternatIOnal Organization of Citrus Virologists. (Ed.) E.C~ Calavan, pp. 79-90. Semanclk, 1.S. and Weathers. L.G. 1968a. Characterization of infectious nucleic acid associated with mfection by exoconis Virus of citrus. Phytopathology, 58 : 1067. Scmanclk, l.S and Weathers, L.G. 1968b Exocortls VJnIS of CitruS; Association of mfectivlty with

46

VIRUS AND MYCOPLASMA DISEASES OF FRUIT CROPS IN INDIA

nucleic acid preparations. Virology, 36 : 326-328. Shanna, D.C. and Pandey, P.K. 1983. Leaf yellow mid-vein, a previously under scribed disease of citrus. 1m. J.Trop. PI.t : 149-152. Singh, A.B. 1.969. A new disease of Carica papaya in India. PI. Dis. Reptr 53: 257-269. Singh, S.J. and Sastry, K.S.M. 1974. Wilt of pinea!'l'le-anew virus disease in India. Indian Phylopath. 24 : 298-303. Singh, S.1., Sastry, K.S.M. and Sastry, K.S. 1975. Little leaf disease of grapevine from India. Curr. Sci . . 44: 26-28. Summanwar, A.S. and Marathe, T.S. 1982. Diagnostic technique for the detection of bunchy top and infectious chlorosis in banana suclc:ers.. Curro Sci. 51 : 47-49; Swingle, W.T. and Webber, H.1. 1896. The principlediseases'of citrus fruilS in florida, USDA, Div. Veg. Phys. Palh. Bull. B : 42. ! \ Tanaka, S. and Kishi, K. 1963. Studies on indicator plants of citrus viruses. I. Mechanical inoculations on leguminous plants with sap from satsumadwarftree.AlIn.Phy'opath. Soc. Japan 28: 262-269. Tanaka, H. and Imada, 1. 1974. 'Mechanical transmission of viruses of satsuma dwarf, citrus mosaic, navel infectious mauling and natsudai-dai dwarf to herbaceous plants. 1'1'. 141-145. Proceedings of 6th Conference of International Organization of Citrus Virologists. University of California, _ Division of Agricultural Science, Richmond. Tanaka. H. and Imada. J, 1976. 'Purification of viruses of citrus mosaic and navel orange infectious mottling'. 1'1'. 116-118. Proceedings of 5th Conference of International Organization of Citrus Virologists. IOCV, Riverside, California. Tanaka, H. and Yamada, S. 1972. 'Evidence for a relationship among the viruses of satsuma dwarf. citrus mosaic, navel infectious mouling, natsudai-dai dwarf citrus variegation and citrus crinkly leaf'. pp. 71-75. Proceedings of 5th Conference of International Org;mization of Citrus Virologists. University of Florida Press, Gainesville. Tanaka, H., Kishi, K. and Yamada, S. 1965. 'Research on the indicator plants of satsuma dwarf and' Hassaku dwarf viruses-'. pp. 260-267. Proceedings of 3rd Conference of International Organization on Citrus Virologist. University of Florida Press, Gainesville. Tanaka. H., Yamada. S.· and Kishi, K. 1971. Symptom and occurrence of'navel orange infectious mottling and matsudal-dai dwarf. Bull. HOTI. Res. SllI. B 11 : 141-147. Vanna, P.M., Rao, D.G. and Capaor, S.P. 1965. Transmission of tristeza virus by Aphis CTaccivora (Koch) and Dacynotus Jaceae. L.lndian J. Ent. 27 : 67-71. Vanna, P.M., Rao. D.G. and Vasudeva,R.S. 1960. Additional ~ectoroftristez.a disease of citrus in India. CUTT_ Sci. 29 : 359. Vasudeva. R.S. and Capoor. S.P. 1958. Citrus disease in ~ombay State. Bull- PI. PTOI. 6: 91. Vasudeva, R.S., Varma, P.M. and Rao. D.G. 1959. Transmission of citrus decline virus by To:xopteTa cilTicidus Kirk. in India. CurT. Sci. 28: 418. Vogel. R. and Bove, I.M. 1964. Stem-pitting sur bigaradier euur orange 'tarocco' en corse une maladie a virus. Fruits, 19 : 269-274. Wallace, I.M. (Ed.) 1959. 'Citrus virus diseases'. Proceedings of 1st Conference of International- Organization of Citrus Virologists. University of California, Division of Agricultural Sciences, ' Berkeley, 243 pp. Wallace,I.M. 1953. A virus mduced vem enatlon in citrus. Cilrus Leaves 33: 22-24. Wallace,1.M. 1960. Woody galls of CitruS associated with vein enation virus infection. Pl. Dis Rep/T 44: 580·584. Wallace, I.M. and Drake, RJ. 1962. Tatter leaf, a previously underscribed Virus effect on citrus. Pl. Dis. Rep1T46: 211-212. Wallace, I.M. and Drake, RJ. 1968. 'Citrange stunt and ring-spot, two preVIOusly underscnbed virus diseases of citrus'. 1'1'. 177-183. Proceedings of 4th Conference of International Organization of Citrus Virologists. University of Ronda Press. Gainesville. Wallace.l.M .• Oberholzer,P.C.J. and Hofmeyer,l.D.1. 1956. Distribuuonofviruses oftnsteza and other diseases of citrus in propagative material. PI. Dis. ReplT 40: 3-10. Weathers, 1957. A vem yellowing disease of Citrus caused by a graft transmiSSible virus. Pl. DIS. Replr 41 : 741-742. Weathers, L.G. 1960. Yellow vem disease of citrus and studies of interactions between yellow vem and

L.a..

VIR US DISEASES OF TROPICAL AKD SUB-TROPICAL FRUITS

47

other viruses of citrus. Virology, 11 : 753-764. Weathers, L.G. 1961. 'Responses of citrus to concurrent infc:aion with two or more unrelated viruses'. Proceedings of 2nd Conference of International Organization of Citrus Virologists. pp. 187-196, University of Florida Press, Gainesville, Florida. Weathers, L.G. 1965. Transmission of exocortis virus of citrus by CwscUla subinc/wsa. PI. Dis. Replr

49: 189-190. Weathers, L.G., Greer, F.C. and Harjung, M.K. 1967. Transmission of exoconis ·virus of citrus of herbaceous hosts. PI. Dis. Replr 51: 868-871. Yamada, S. and Sawamura, K. 1952. Studies on the dwarf disease of satswna orange. Cilrws IUlShu Marcovitch. Preliminary report. Tokai·Kinki A,ric. Exp. Sill. BI4II. 1 : 67·71. Yerne war, S.I. and Mali, V.R. 1980. On the identity of a sap transmissible virus of papaya in Marathwada. Indian J. Mycol. PI. Palh. 10: 155·160. Yora, K., Ooi, Y., Raychaudhuri, S.P. and Ahlawat, Y.S. 1977. Infectious variegation of citrus in India. Calif. Cilrograph. 62 : 432. Zanardi, D., Anneda, G. and Follesa, B. 1967. Levirosi degli agruoni in Sardegna. Sardegna Assessorato Agricultural a Foreste, 54 pp.

4

Virus Diseases of Other Fruit ,Crops OrHER fruits in the country arc grown on a small scale except mango which occupies the major area under cultivation (1,001.5 million ha). The total area under all other fruits is about 0.543 million hectare with a production of 3.085 million lonnes.

Fig Mosaic This disease of fig (Ficus palmata) was reported from Kumaon and Shimla hills (Bhargava and Bist, 1962; Nagaich and Vashisth, 1962). Affected leaves show irregular yellowish green blotches scattered all over the surface. Sometimes vein-banding also develops (Fig.29). The disease is transmissible by grafting. The vector is a !11ite, Aceriaficus (Vashisth and Nagaich, 1968). The virus can infect Ficus carica. F. nemosalis and Morus indica in addition to F. palmata ~Vashisth and Nagaich, 1965). Virus Diseases of Mulberry Mulberry (Morus indica and M. alba) is mainly grown as host for silkworm (Bombax mori) and hence plays an important role in sericulture. Two important virus diseases, viz., yellow-net vein and mosaic, have been recorded on mulberry in Darjeeling district of West Bengal. Yellow-net vein. The disease was first observed on mulberry variety 'Koksu' in Kalimpong. Later, the disorder was recorded on mulberry plantations at Siliguri, Bcrhampur and MaIda in West Bengal. The characteristic symptoms of the disease appear in March-April as yellowing of leaf veins. However, interveinal portion remains green. It is easily transmissible by pen' grafts and in arch grafts (Raychaudhuri et al., 1961). Several Morus species/varieties and clones are susceptible to yellow-net vein infection (Raychaudhuri et al., 1965). The vector of the disease is whitefly, Bemisia sp. (Raychaudhuri et al .. 1966). Mosaic. A disease with typical mosaic symptoms, often associated with curling and puckering of leaves, was first observed on mulberry variety 'China Black' in Kalimpong (Raychaudhuri et al .• 1962). The causal virus is transmissible by mechanical inoculations and by aphids Rhopaiosiphum maidis. Myzus persicae and Aphis gossypii (Raychaudhuri et al., 1962, 1965; Chattcrjee and Raychaudhuri, 1963, 1965). The virus infects a large number of mulberry varieties and clones (Raychaudhuri et al .• 1965). Physical properties of the virus were studied by Raychaudhuri et al. (1965). The virus can withstand an exposure up to 50°C for 10 minutes but not at 60"C. Dilution end-point is between I :2000 and I :4000 and longevity in vitro is I 0 and 15 days .at room temperature (28"-30°C). Recent studies indicate that mosaic is more commonly distributed in northern Bengal. However, yellow-net vcin symptoms were rarely observed during spring

VIRUS DISEASES OF OTI-IER FRUIT CROPS

49

months and, when such plants were maintained in the glasshouse at Kalimpong, the symptoms disappeared and the plants carried only mosiac symptoms (Ahlawat, unpublished). TherefOre further studies are necessary to establish yellow-net vein disease as a separate one from mosaic disease. Virus Diseases of Cape Gooseberry Cape gooseberry (Physalis peruvian a) is grown mostly in the kitchen gardens. This is an annual crop. and fruits are not very popular among masses. A mosaic disease of cape gooseberry is of common occurrence in India (Capoor and Sharma, 1965; Nariani and Sharma, 1971). In addition to this disease leaf-curl disease has also been observed in Delhi (Nariani and Pathanian, 1953). Mosaic. This disease is caused by tobacco mosaic virus (Capoor and Sharma, 1965) and cucumber ~ic virus (Nariani and Sharma, 1971). In the field, diagnosis of the causal virus is difficult as the symptoms produced by both the viruses do not differ much and dual infections are also common. The disease is characterized by typical mosaic mottling, puckering, dark green patches or blisters on leaves (Fig.30). The symptoms of infection by tobacco mosaic virus (TMV) are premature defolIation of leaves and high percentage of fruit drops without ripening. Whereas in plants affected by cucumber mosaic virus (CMV) the leaves are reduced greatly in size and become malformed and distorted. Only a few fruits are set in on affected plants. Both the viruses are transmissible by mechanical means. There is no vector for the disease caused by TMV. The CMV has aphid vectors, Myzus persicae and Aphis gossypii. Both the diseases can be diagnosed by their respective physical properties, indicator host (s) and by particle morphology. Leaf-curl. This disease occurs either singly or in combination with mosaic. Leaves of affected plants show curling, puckering and become smaller and show dark-green enations on the veins oflower surface. The disease is not sap transmissible but can be easily transmitted by whit«Oy Bemisia tabaci (Nariani and Pathanian, 1953). The causal virus has been identified as tobacco leaf-curl virus. Jujube Disease Jujube (Ziziphus mauritiana) is a commerical fruit crop. It is cultivated in semi-arid and arid tracts of the country. The fruit is rich in minerals and carbohydrates. Witches' broom. A witches' broom disease was observed in the orchards of Pune University, Pune, Maharashtra and also in adjacent orchards. During 1973, about one-third of the ber orchard was found affected with this disease. In nature, the disease is also associated with dieback symptoms. Phyllody is a characteristic symptom if the plants are infected one y.ear before attaining the flowering stage. The affected trees may produce small fruits but do not flower in subsequent years. Shoots of infected trees are weak: and elongated, and cannot stand upright. The axillary buds proliferate and produce many small, thin and weak secondary branches, covered with small yellow leaves giving it a bushy appearance. The disease is transmissible by grafting. The symptoms appear after two-and-a-half months as production of abundant small leaves. Attempts to transmit the disease through sap inoculations on Ziziphus and herbaceous hosts failed. Affected plants

so

VIRUS AND MYCOPLASMA DISEASES OF FRUIT CROPS IN INDIA

30

Fig. 29. Fig leaf with mosaic disease.

Fig. 30. Mosaic symptoms on capl gooseberry due to cucumber mosaic vi rus.

Fig. 31. Citrus tristeza virus particle (right), panicle in ISEM test (left).

I

VIRUS DISEASES OF OTHER FRUIT CROPS

51 ,

in glasshouse when sprayed with tetracycline antibiotic at a concentration of 1,000 ppm develop new shoots with normal-sized green leaves (pandey et al., 1976), suggesting the involvement of mycoplasma-like organisms with this disease. REFERENCES Bhargava, K.S. and Bist, N.S. 1962. 'Fruit tree virus disease investigations in Uttar Pradesh'. Proceedings of 4th Symposium on Virus Diseases of Fruits and Trees in Europe. Lyngby (1960), Tidsskr.Planteavl, 65, Saemwnmor, pp. 196-20l Capoor, S.P. and Sharma, D.C. 1965. Studies on cape gooseberry mosaic disease. Indian Phylopalh. 18: 58-65. Chatterjee, S.N. and Raychaudhuri, S.P. 1963. Additional vectors of mulberry mosaic. Indian Phytopalh. 16 : 243-244. Chatterjee, S.N. and Raychaudhuri, S.P. 1965. A note on aphid transmission of mosaic dIsease of mulberry. Indian Phylopath. 18 : 319-320. Nagaich, B.B. and Vashisth, K.S. 1962. Mosaic of Ficus sp.in India. Curro Sci. 31 : 166-167. Nariani, T.K. and Pathanian, P.S. 1953. Physalis peruviana L., a new host of tobacco leaf-curl virus. Indian Phylopath. 6 : 143-145. Nariani, T.K. and Sharma, B.C. 1971. A mosaic disease of cape gooseberry caused by Cucumis virus. I. Indian Phytopalh. 24: 383-385. Pandy, P.K., Singh, A.B., Nimbalkar, M.R. and Marathe, T.S. 1976. A witches' broom disease of jujube from India. PI. Dis. Replr 60: 301-303. Raychaudhuri, S.P., Chatterjee, S.N. and Dhar, H.K. 1961. Preliminary note on the recurrence of yellownet vein disease of mulberry. Indian Phylopalh. 14: 94.95. Raychaudhuri, S.P., Chatterjee. S.N. and Dhar, H.K. 1962. A mosaic disease of mulberry. Indian Phylopalh. IS: 187-189. Raychaudhuri, S.P., Ganguli, B. and Basu, A.N_1965. Further studies on the mosaic disease of mulberry . PI. Dis. Replr 49 : 981. Raychaudhuri, S.P., Ganguli. B. and Basu, A.N. 1966. 'Virus disease of mulberry in India'. Plant Disease Proceedings of 1st Symposium on Plant Pathology. pp. 274-277. Vashisth, K.S. and Nagaich. B.B. 1965. Morus indica-an addItional host of fig mosaic. Indian Phy'opa,h. 18 : 135. Vashisth, K.S. and Nagaich, B.B. 1968. Aceriaficus (Colte) as vector of fig mosaic in India. Indian J. Ent. 30 : 322.

5

Management of Virus and Mycoplasma Diseases of Fruits FOUR decades ago investigations on the virus and virus-like diseases of fruits were taken up at different research centres in India. Since then several diseases caused. by these pathogens have been discovered. In most of the cases, we are ignorant about the natural spread of th,ese viruses but in others like citrus tristeza, papaya mosaic and leaf-curl vector(s) have been well-established. Because most of the fruit trees are propagated by vegetative propagation, primary spread of these pathogens through this means cannot be ruled out. In apple mosaic, apple rubberywood and citrus psorosis, where no vector transmission is yet known, vegetative propagation appears to be the only method of spread. Therefore it is rather easy to control such viruses by budwood certification programmes. For efficient management, reliable and quick methods of 'pathogens' detection is important. The following methods are usually employed to detect viruses and virus-like pathogens affecting fruit trees, DETECTION OF PATHOGENS Indexing This is one of the most important approaches to detect the viruses in fruit trees. The planting materials are seed, stem, cuttings and buds. ,Since majority of the viruses affecting fruits are not seed-borne, seedlings of such fruits can be utilized for rootstock, The bud/scion free from viruses can be determined by index ing, Following methods are used for indexing. Indicator host (5). Despite dramatic advances in biochemical and immunoassay technology, the indicator plants still remain as the eye through which we can see and indcntify most of the viruses (Table 1). Therefore any programme for the eradication of fruit viruses must include a plant laboratory with facilities for producing the finest plant growth (Nauer et al., 1968; Roistacher, 1976). It is important that indicator plants develop vigorously with clear leaf flushes free of micronutrient dcficiencies or excesses, and maintained as free as possible of insect pests. Temperature control is important because in most of the cases virus detection is temperature dependent. Therefore an ideal facility must have provisions for a cool room ora section held at 25°-30°C/18°-20"C anda warm section at 32°-40"C/ 24°-30°C (maximum day temperature/minimum night temperature). Electron microscopy (EM). The virus particles are visible only in electron microscope. Though this instrument is' expcnsive and each laboratory cannot afford to have it but wherever it is aV,ailablc is for utmost l,lse in detecting viruses in the planting materiill. It is difficullLO use EM of routine indexing, but is of great help in limited cases like screening of nucleus material. Electron microscopy of viruses affecting fruits can be carried out with purified preparations, which is necessary if fine details of structures are to be studied. A most critical considcra-

53

MANAGEMENT OF VIRUS AND MYCOPLASMA DISEASES OF FRUITS

Table 1. Indicator plants and symptoms produced on them by the virus and mycoplasma-like agents affecting fruit crops Disease

Indicator host

Symptoms on indicator host

Non-pareil almond

Yellowing of finer vems or yellow necking at the margin of the leaves

Flat limb

Apple variety 'Gravenstein'

Flattening of shoots and twisting of small branches

Leaf pucker

Apple variety 'Golden D~licious'

Puckering and dlstonion of the leaves, pu~le blotching on fruits

Little leaf

Apple variety 'Lord Lamboume'

Smalling of leaves, failure of bud opemng

Mosaic

Apple variety 'Lord Lamboume'

Mild chlorosis, vem banding and yellow patches according to the mild, intennediate and severe strains respectively

Rough skin

Apple variety 'Boskoop'

Rough brown patches on fruit skin

Rubberywood

Pear seedling

Chlorotic spots and dark brown patches on the leaves

'Lord Lamboume'

Elasticity

Star cracking

Apple variety 'Cox's Orange Pippin'

Star-shaped cracks on fruits, upright growth and dieback of branches

Tumor

Apple variety 'Laxton's Exquisite'

Swelling at the bifurcation point of branches

Apricot variety 'Kaisha'

Mottl ing of leaves

Apricot vanety 'Blenhein'

Oak-leaf pattern and yellowing of leaf margms

Banana variety

Bunchy appearance of affected plants, reduction and upward roiling of leaves Chlorotic patches or stripes on leaves

Almond Mosaic

Apple

Apricot Mosaic Oak-leaf pattern Banana Bunchy top

'Basral'

Infectious chlorosis or mosaic

Banana vaTiety 'Belchi'

In

wood

Table I (Contd)

54

VIRUS AND MYCOPLASMA DISEASES OF FROIT CROPS IN INDIA

2

3

Der (Ziziphusjujuba) Witches' broom

Ber seedlings

Phyllody and smalJing of leaves

Cape gooseberry Mosaic

Nicoliana

Necrotic lesions on inoculated leaves or ,eve~ mouling according to TMV/CMV infection respectively

g/ulinosa

Tobacco

Curling and puckering of leaves

'Blackhean' cherry

Variegated leaves

Plum and peach

Ring-spot and shot-hole on leaves

Sweet orange, mandarin, lemon

Leaf flecking andl or vein clearing

Cachexial xyiC)jI(lrosis

Troyer citrange or rusk citrange

Gum near union, pits in ,wood and gum in baric

Concave gum

Sweet orange

Oak-leaf pattem and flecks in young leaves

Crinkly leaf

Sour orange, lemon

Crinkling of leaves, leaf flecking

Dweet mottle

Dweet tangor

Psorosis-Iike mottle on leaves

Exocortis

Enog citron

Leaf and stem epinasty, cracking of mid-vein, browning of petiole and leaf tip

Greening

Mosambi. Sikkim orange

Leaf blotching. mottling and chlorosis

Impietratura

Cilrus deCWI'IIlM

Hardening of fruits, gum in albedo and psorosis-like leaf symptoms, gum pockets in young twigs

Infectious variegation

Citron, sour orange

Variegation and distortion of leaves

Leaf-curl

Sweet orange

Extreme curling of leaves, stuntio8

Mosaic

Darjeeling orange 'SathgJldi'

Mottling, smalling and wavy margin of leaves,bright yellow patches on leaves

Leaf-curl Cherry Marble mosaic Tatter leaf Citrus Blind pocket

Table 1 (Contd)

MANAGEMENT OF VIRUS AND MYCOPLASMA DISEASES OF FRUITS

2

55

3

Rubberywood

Lemon, mandarin

Geotropic habit of branches, mild chlorosis ofleaves

Psorosis-A or ringspot

Sweet orange cv. mosambi kinnow

Clear flecks along veinlets, ring-like pattern on mature leaves

Satsuma dwarf

White sesame, satsuma orange

Necrotic spots and streaks on sap inoculated sesame plants, boat-shaped leaves on satsuma mandarin

Stubbom

Sweet orange, tangelo

Stunting and leaf moule, smalling of leaves and shortening of internodes

Tristeza

Kagzi lime

Veinlet clearing, stem pitting

Vein enation and woody gall

Kagzi lime, rough lemon

Galls on stem and branches, enations on undersides of vein lets of Kagzi lime

Yellow vein

Kagzi lime, Etrog citron

Bright yellow corky vems of leaves

Mosaic

Ficus carica

Irregular yellowish green blotches on leaves

Gomphrena globosa

Chlorotic spots on inoculated leaves followed by systemic chlorosis, mottle and leaf deformity

'Merlot Noir' variety of grapevine

Proliferation of axillary buds, zigzag stem, smalling of leaves

Rubus sp.

Severe chlorosis of leaves, chlorotic rings and oak-leaf pattern on leaves

Mulberry variety 'China Black'

Mouling and puckering of leaves

Mulberry variety 'Koksu'

Yellowing of leaf veins

Fig

Grapevine Fjln-leaf

Liule leaf

Himalayan raspberry Mosaic and ring-spot

Mulberry Mosaic Yellow-net vein

Table 1 (Contd)

vrn. US AND MYCOPl:.ASMA DISEASES OF FR UIT CROPS IN INDIA

56

I '

Papaya Leaf-I:url

2

3

Datura strampnlum, Petunia hybrida, lobacco Cucumis sativus and Cucurbita sp.

Curling of leaves

Chenopodium amaranlic%r

Necrolic lesions on inoculated leaves

'July AlbelU' peach

Slem necrosis and oozing of gum from stem and branches

Mosaic

Peach var. 'J.H.Hale'

Profuse branching with shon internodes and oak-leaf paltern on young leaves

Necrollc leaf-spol

Cucurbita maxima var. 'Buttemul'

Slunling of inoculated planlS, mOllling of leaves

Mosaic Ring-spol Peach Gummosls

Mosaic mOlding of leaves

'X'

'Celery', 'Periwinkle'

'Chlorosis of leaves

Yellows

Prunus padas

Roselling Qf inoculaled planls

Mosaic

Pear seedling

Chlorolic SpolS or rings and oak-leaf pallem on leaves

Pineapple

Wilting of affecled planlS

'Santa Rosa' plum

Small, pale yellow 10 white spolS on the leaves

Plum ~eedlings and varielies

Yellowing of leaf veins

'Bird Cherry', salsuma plum

Mosaic mOlding of young leaves

Cydonia sp.

Yellow flecking and severe moltling of leaves

Pear

Pineapple Will Plum Creamy-white SPOl Line pattern

Mosaic Quince YeHow mosaic

tidn for purification of viruses in fruit trees is that these viruses usually exist in very low concentrations, may be irregularly distributed, or temporarily absent during warm summer temperatures. Therefore purification directly from fruit trees is difficult. Hence, attempts should be made to transfer fruit viruses to herbaceous hosts by mechanical inocukilions/vector (Kishi and Tanaka, 1964; Tanaka, 1972; Tanaka and Imada, 1974; Boyle et al .• 1954; Ahlawat et al .. 1979). Since many of these viruses are not'mechanically transmitted and vectors have been established 'in limited cases, dodder (Cuscuta sp.) is one of the best methods

MANAGEMENT or VIRUS AND MYCOPLASMA DISEASES OF FRUITS

57

PRINCIPLE

1 . Specific antibody adsorbed to plate (coating)

Wash 2. Add test sample containing mollicute !virus

Wash 3. Add alkaline phosphatase labelled specific antibody

Wash 4. Add paranitrophenylphosphate (PNPP)

5. Colourless PNPP is hydrolyzed tp yellow paranitrophenol if mollicute/virus is present

F~. 32. Diagramatic representation of enzyme Iinked immunosorbent assay (ELISA) technique used for deteclion of viral and mycoplasma infections in plants (Clark and Adams, 1977).

to transfer viruses from fruit trees to suitable hosts (Ahlawat and Dhingra. 1973). Viruses can also be visualized in EM by quick-dip method from diseased leaves or bark extracts. but this method is not proved to be very effective with fruit tree viruses owing to their low concentrations in woody hosts. However. some viruses affecting fruits have been detected and characterized by electron microscopy (Lister et al .. 1965; Sequerira and Lister. 1969; Cropley, 1961; Desjardins, 1969; Semancik and Weathers, 1970; Dias. 1963; Zettler et al., 1968; Paulsen and Fulton. 1969; Sequeiira. 1967; Yora et al .• 1977). Another important method to identify virus and virus-like pathogens (MLOs. spiroplasma and fastidious bacteria) in situ is through ultra-thin sectioning. The pathogen can be easily observed in host cells along with cell organelles. By this method. citrus greening organism and citrus rubberywood mycoplasma have been characterized (Ahlawat. 1987; Naidu and Govindu. 1981).

58

VIRUS AND MYCOPLASMA DISEASES OF FRUIT CROPS IN INDIA

Serological Detection Double-dirfusion. Various types of serological tests used for plant viruses are also applicable to fruit viruses. One of the serological tests most commonly used is the double-diffusion agar gel. By this method, relatively large numbers of tests can be set up in a short time in one or two petri-dishes using crude or clarified extracts. Washed ion agar 0.6-0.7% made up with water and with 0.02% sodium azide is added just before solidification to avoid microbial growth. Wells, 6 mm in diameter, spaced 4 mm apart are convenient. Templates can be made which will punch a circle of 6 wells at equal distance from the central well. Tests involving diffusion of antigen in agar cannot be applied to long filamentous viruses such as apple chlorotic leaf-spot and citrus tristeza unless the virus is disrupted into small pieces that will diffuse readily. A problem commonly encountered jn serological tests with fruit tree viruses is that the test antigen concentrations are not sufficiently high to give a visible reaction. There arc number of ways. to cope with such problems. Wells can be spaced more closely in agar plates; antiserum can be appropriately diluted to avoid reactions at the edge of antigen well that might be overlooked; virus can be transferred to a host in which it will rcach a much higher concentration within a few days; and virus may be concentrated by high speed centrifugation from dilute extracts, re-suspended in a small volume of buffer and serological tests run with this concentrate including impurities in agar-gel tests. Viruses by this serological method have been detected in several fruit trees (Cropley, 1960; Regenmonel and Engelbrecht, 1962; Tremaine ec ai., 1964). Relationship among viruses affecting different plant species could also be established by double-diffusion tests (Cadman and Lister, 1961; Yarwood and Sylvester, 1959). In cases where concentration of the virus in the host is very low and difficult to detect in EM in crude sap, the virus can be detected by electron microscope / serology technique briefly given below. Electron microscope serology. The tcchnique is most appropriately known as immunosorbent elcctron microscopy (ISEM). Dcrrik (1973) 'trapped' viruses on antibody-coated grids (ACG). The procedure involves the floating of a carboncoated grid on diluted antiserum (1: 10 to 1: 1000 depending on the titre of antiserum). The grid is then covered with a sap homogenate so that the antibodies trap virus particles from the solution, with the result that a higher concentration of particles become attached to the grid than is normally possible by the usual dip method. The test was effective to detect citrus tristeza and citrus psorosis viruses (Garnsey et aI., 1980; Ahlawat, unpubli'shed). In a slightly modificd ISEM tec~nique, the antigen is mixed with antiserum prior to.its being placed on a grid for EM examination. The virus particles are linked with amibodies in groups which is generally referred to as 'clumping' (Milne and Luisoni, 1975). In an another modification, the grids are first coated with antigen (virus preparation or sap homogenate) and then floated on antiserum so that the virus particles are coated or 'decorated' with antibodies. The sensitivity of the technique is sometimes increased by trapping particles on the grid and then decorating them with antibodies (Noel et al., 1978). They detected particles of plum-pox virus in trees by this method. This technique is el\tremely useful for indexing nucleus seed material to be used in certification programmes. Recent)y, we have used this technique for the detection of tristeza virus from several citrus species (Fig.31). .

MANAGEMENT OF VIRUS AND MYCOPLASMA DISEASES OF FRUITS

59

Enzyme-linked immunosorbent assay (ELISA). Though ISEM is a highly sensitive and useful technique for virus indentification. it is not practical if large number of plant samples are to be tested. Where electron microscopic facilities are not available. detection of viruses in large number of samples by ELISA has been found more convenient and useful. The technique known as 'double antibody sandwitch' (DAS) has been widely used in the detection of citrus and other fruit viruses (Bar-Joseph el at .• 1979; Garnsey el at., 1979). Clark and Adams (1977) have given a schem

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plantings in commercial orchards. Non-chemical control of insect vectors in fruit trees by use of barriers and reflective. mulches. oil sprays and deployment of predators has not been worked out and appears of little value in tree crops.

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MANAGEMENT OF VIRUS AND MYCOPLASMA DISEASES OF FRUITS

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Cross-protection The principle involved in cross-protection comprises prior infection with a mild strain of a virus so that d,llnuge due to subsequent infection by a severe strain of the same virus can be reduced or eliminated. Cross-protection could be demonstrated with viruses which have distinct strains. There are certain limitations in this method such as (i) mild protecting strain may spread LO other hosts in which its effect might be more severe, (ii) cross-protection may not be complete or it may breakdown, (iii) the protecting virus may react synergistically wi,th a second unrelated virus, and (iv) protecting virus may mutate to a severe form that could cause destructive disease. However, despite all the difficulties anticipated, the method has been effective with following virus diseases of fruit crpps. Citrus tristcza. Tristeza virus causes lethal disease in certain stock-scion combinations. Control by using tolerant rootstocks is not possible with some citrus species. Cross-protection experiments were conducted to meet thethreat of citrus decline due to tristeza virus. This method was firstaltempted in 'Brazil by Muller and Costa (1977) and Costa and Muller (1980). Mild SLr;lin was detected in tristeza (Grant and Costa, 1951; Olson, (956) and this strain protected plants 'against severe strains in tests with aphid vectors. The experiments conducted ill Brazil further revealed that isolates selected on the basis of mildness of symptoms in one citrus species were not necessarily mild in others. Therefore for each citrus species the identification of mild strain is essential to achieve success in controlling the disease. The protecting capacity of selected mild isolates has remained unchanged through several successive clonal propagations from the originally protected trees. Tristeza-tolerant stock-scion combinations of citrus also give better yields when protected by mild strains than when unprotected and exposed to natural infection (Muller and Costa, 1977; Costa and Muller, 1980). Similar experiments were also successful in Australia in grape fruit, but protection was successful for three years and then it broke down (Fraser et al .• 1968). In India, strains oftristeza virus have been separated from affected citrus trees, stabilized and identified for their characteristic behaviour in Indian Kagzi lime (Capoor and Rao, 1967). They identified the severe strain (Tt), the mild strain (Tm) and seedling yellows (Ts) and demonstrated cross-protection. However, these studies were mostly restricted to laboratory condit:ons. Balaraman and Ramakrishnan (1978) demonstrated crossprotection of acid lime with a mild strai,n of tristeza virus in the field. Papaya ring-spot. Two mutants of papaya ring-spot virus were obtained by treating extracts with nitrous acid. These mutants were symptomless in papaya (Yeh and Gonsalves, 1984). These isolates protected papaya against the severe strain. The problem of infecting large number of seedlings can be overcome by pressure spray inoculations with carborundum at the rate of 40g/Iitre in 1:10 dilution of inoculum made in om M, pH7.0 phosphate buffer. A pressure of8 kg/ cm 2 is enough for inoculation. Concave gum and psorosis of citrus. Mild strains of these viruses protect citrus plants against severe strains (Roistacher and Calavan, 1965). Recently, a mild strain of psorosis is identified in India (Ahlawat, 1987) and may be used for cross-protection experiments. However, no other data are available to suggest that cross-protection would be a suitable control measure for these diseases.

66

VIRUS AND MYCOPLASMA DISEASES OF FRUIT CROPS IN INDIA

Temperate fruit virus diseases. Naturally occurring mild strain of peach mosaic protected peaches against graft inoculation with severe strains (Bodine, 1942). Cochran (1954) suggested cross-protection as a control measure in areas where peach mosaic is wide spread and other means of control are ineffective. Cross-protection in viruses of stone fruits has been demonstrated by Ellenberger (1962) and Marenaud and Bernhard (1968). Howell and Mink (1984) reported a widely distributed mild strain of rugose mosaic in 'Bing Sweet' cherry orchards. This mild strain restricted the spread of the rugose mosaic disease. Several strains right from very mild to severe ones have been reported in apple mosaic virus (Chamberlain et al., 1964; Posnette and Cropley. 1956). Trees infected with mild strain showed protection against severe strains. In India, cross-. protection has been demonstrated with apricot mosaic virus (Nagaich and Vashisth. 1962; Dhingra and Ahlawat. 1979). Welsh and May (1973a.b) found crossprotection of a severe strain of apple leaf pucker and apple blotch viruses in certain clones of apple cullivars. Although cross-protection has been attempted as a control measure only for a few viruses. yet the success wilh tristeza provides an encouraging result suggesting that it may be effective for many others especially in perennial crops. Suppression of Disease Symptoms by Chemicals No chemical has been found effective against plant viruses so far, but Tomlinson et al. (1976) reported that fungicides such as Benlate and Bavistin which contain methyl bcnzimidazol-2YI - carbomate reduced the severity of yellowing symptoms by beet western yellows virus in lettuce. In India. Benlate and Bavistin have been found effective and reduce the symptoms caused by greening pathogen in citrus plants (Thind et al., 1987). Suppression of disease symptoms by these fungicides is thought to be dye to their cytokinin-like activity which delays the breakdown of the Chloroplast by the virus. Their role for commcrical application in fruit trees remains to be assessed. This mcthod of disease control in fruit trees has been successfully employed in case of infection by mycoplasma-like organisms; phloem and xylem limited fastidious prokaryotes including Spiroplasma citri. M9st of these organisms are susceptible to tetracycline or penicillin therapy. Suppression of' X' disease symp- . toms in peach by oxytetracycline hydrochloride has been reported in India and elsewhere (Rosenberger and Jones. 1977; Ahlawat et al., 19..84). Tetracycline antibiotics like aureomycin (chlortetracycline hydrochloride), achromycin (tetracycline hydrochloride) and ledermycin (dimethyl chlortetracycline hydrochloride) were effective against citrus greening disease (Nariani el al., 1975; Raychaudhuri el al., 1977). Recently. greening symptoms were suppressed by a drug (Ahlawat et al., 1989). Oxytetracyline hydrochloride was effective against the pathogen of little-leaf disease of grapevine (Singh et al., 1975). These chemicals may be given to diseased plants by foliar sprays, root or shoot immersion and tree injections (Sinha. 1979). However, in India there is a wide scope to control MLO disease by these drugs. Remission of symptoms by tetracycline antibiotics treatment is temporary and the plants re-develop them after the treatment is stopped. Perhaps continuous treatmclll for longer pcriods using higher doses may provide complete recovery. Elim ination of Viruses in Planting Materi .. ! Use of nucellar lines and tissue,culture. In crops where polyembryony is

MANAGEMENT OF VIRUS AND MYCOPLASMA DISEASES OF FRUITS

67

well known. nucellar lines are of great advantage to obtain virus-free plants. It has been widely used in citrus. The use of nucellars as a means of bypassing 'viruses' may now be outdated because nucellar lines take 4-8 years to come into fruiting and many lines do not bear fruits. The fruit quality of nucellar lines with some exceptions is poorer than the lines from which they were originally derived. Followings are the other undesirable juvenile characteristics associated with nucelJars: Upright growth habit, excessive tree vigour. alternate bearing. late flowering and fruiting, unequal fruit distribution and more rapid deterioration in the quality of the fruits. Therefore recent techniques like shoot-tip grafting for the elimination of pathogens from bud wood and the uniform true-to-type progeny obtained by shoot-tip grafting (Navarro. 1981; Navarro et al., 1974) have become more popular to eliminate viruses from \Voody fruit plants than by ,nucellar lines. In India, to develop virus-free true-to-type plants using tissue culture technique has been tried by Raychaudhuri and Mishra (1966) and Mitra (1982). Viruses from the planting material have been eliminated from pineapple (Walkey, 1978), apple (Campbell, 1962), gooseberry (lones and Vine. 1968), strawberry (Miller and Belkengren, 1963; Mullin eta/., 1974), banana (Berg and Bustamante, 1974) and raspberry (putz, 1971). Recently, tissue culture techlJiques have been developed to propagate virus-free papayas (R.M. Pande, personal communication). This will help to develop quality papayas in future. In citrus. a shoot-tip grafting technique is developed which elim-inates viruses from planting material (Navarro et al., 1974). In this method. a very minute shoot tip consisting of the meristem and 2-4 leaf primordia measuring 0.14 to 0.2mm is grafted on media-raised rootstock. Nearly all known citrus viruses have been successfully eliminated by this technique (Koizumi, 1984; Navarro, 1981; Roistacher, 1977). This technique was found very useful even to eliminate heattolerant pathogens like exocortis and cachexia viroids of citrus. which are otherwise difficult to eliminate. A combined procedure using thermotherapy and shoottip grafting is very useful to eliminate perhaps most if not all viruses from woody fruit trees Heat therapy. Two types of heat therapy is normally used to eliminate viruses from fruit crops: (i) Exposing bud sticks or scions to high temperature for shon period. and (ii) maintaining potted trees at lower temperatures for much longer periods. Techniques for heat-treating budwood have been reviewed in detail (Roistacher, 1977; Dhingra and Raychaudhuri, 1970). Preconditioning of plants prior to their use is vital to eliminate viruses (Roistacher and Calavan. 1972). Plants should be grown at wru:m temperatures (32°-40°C day and 26°-30°C at night) for one to three months before budwood treatment. Buds cut from preconditioned plants are grafted on rootstocks. To eliminate citrus viruses, for example, budded plants are placed in a chamber at high humidity and at an initial temperature of 38°/30°C (38°C for 16 hours with light and 30°C for 8 hours in the dark). After one week the temperature is raised t040°/3()"C. The budded plants are kept at this temperature for 8-12 weeks and then removed to the glasshouse. New growth is then indexed to verify inactivation. Another thermotherapy method is the treatment of preconditioned bud-sticks in an incubator. In India, thermotherapy has successsfully eliminated some viruses of citrus including greening pathogen (Nariani et a/., 1975). Similarly. pathogens of temperate fruits like apple mosaic virus and rubberywood mycoplasma are eliminated by heat therapy (Dhingra and Raychaudhuri, 1970; Ahlawat and Dhingra. unpublished). In California. cilrus

68

VIRUS AND MYCOPLASMA DISEASES OF FRUIT CROPS IN INDIA

tristeza virus complex including seedling yellows and stem pitting, psorosis-A and B, concave gum, impietratura. infectious variegation, vein enation and tatter leaf were eliminated by heat treatment but exocortis. cachexia viroid and stubborn pathogen could not be eliminated (Roistacher, 1977). Heat therapy has a wide scope to eliminate viruses from vegetativelx propagated fruit trees and is an area of extensive research

Budwood Certification Programmes Once clean stock is produced. a programme for its long-term maintenance and for the distribution of certified bud wood to growers can be organized. Certification programmes will be varied depending on country's specific needs. Basically it involves a nucleus or bank of selected plants which are virus-free. indexed, and true-to-type mother or foundation trees from which buds are collected for increase in a certified increase block. These increase blocks are usually maintained for a limited period of 1\12-3 years to protect against chance of off-type mutations and possible reinfection by vectors or olher means of spread. New colleclions can be repeatedly made from the nuclear or foundation block trees for new bud wood increase blocks. Mother trees must be continuously indexed for the presence of viruses. Buds from the increase block trees may be distributed to the growers, or may be used to grow certified trees by the Government for distribution to growers. There are many problems in developing. maintaining and protecting a foundation planting. Prevention of reinfection by insects or by men via mechanical transmission is foremost. An ideal certification programme for citrus. evolved at the University of California, USA (Fig. 33). can be adopted by all other countries with suitable modifications wherever necessary. A decision to develop a foundation block with its supportive indexing facility must be well supported and adequately financed as a long-term programme. There should be policies for education and publicity to inform growers and public of the danger of viruses and the benefits of the virus-free stocks. Other considerations which must be faced are adequate facilities, government regulations, isolation, grower involvement, trained technical personnel, storage, record keeping and means of budwood collection and distribution to growers. The longterm positive benefits while avoiding viruses in propagative budwood by a good certification programme make all efforts worthwhile from both economical and pathological point of view. There are good avenues of certification programmes in temperate fruits and citrus in India. In India, Nariani and Raychaudhuri (1971) suggested a budwood certification programme in citrus which can be tried wilh modifications in the light of present knowledge on the subject. Resistant Rootstock With most temperate fruits, seedlings of the same species or variety are commonly used as rootstock. But in crops like citrus, citrus species or their relatives are used as rooL~tocks. In case of temperate fruits, very little work has been done to establish a resistant rootstock [or any of the known viruses in the country. Tberefore, rootstocks showing resistance against one or more pathogens should be identified. Seed-borne nature of different viruses-must also be established before initiating this programme. In case of citrus fruits, relatively more work has been done all over the world including India. Resistant or tolerant rootstocks against several viruses and myco-

MANAGEMENT OF VIRUS AND MYCOPLAS MA DISEASES OF FRUITS

69

plasma disease have been identified (Nariani el al .• 1973; Ahlawat and Sardar, 1976; Ahlawat el al .• 1979; Cheema el al .. 1982; Fraser and Singh. 1966; Naidu and Ramakrishnan, ] 977). However, horticultural acceptance of these rootstocks has to be assessed. . RECOMMENDATIONS FOR MANAGEMENT OF VIRUSES INNURSERIES 1. 2. 3.

4. 5. 6.

Use only virus-indexed bud wood/suckers. Grow rootstock seedlings from healthy seed from certified trees. Avoid rebudding on rootstocks on which bud has failed. This doubles the chances of introducing viruses. Adjust appropriate spacing to avoid the possibility of natural root grafting. Nursery should be grown away from the main orchard/plantation as it may serve a reservoir of viruses. Rogue abnormal plants from nursery as soon as they are observed. RECOMMENDATIONS FOR VIRUS MANAGEMENT IN ORCHARD

1.

2. 3.

4. 5.

Buy trees or planting materials from nurseries that participate in certification scheme or take necessary precautions in their own independent programmes. Orchardist who grows his own nursery should observe the precautions recommended for nurserymen. Avoid as far as possible the interplanting of indexed nurserystock with established virus-infected trees. Be familiar with the symptoms of virus diseases; be prompt in removal of diseased trees; report occurrence of serious diseases to regular advisory or rcgulatory officials; co-operate with them in eradication programme, when they deem it necessary. Acquire knowledge of host'range of serious viruses and remove wild hosts 'growing near the orchard plantings otherwise it may be hazardous. When introducing cullivars and clones from other regions, adhere rigidly to quarantine precautions to avoid introducing new viruses to your region. FUTURE THRUST

In India, several viruses have been recorded on fruit plants growing in temperate and tropical climates. In most of the cases, the studies are only limited to transmission and host range of the particular pathogen. Hence emphasis should be on proper characterization, etiology, epidemiology, assessment of losses, culturing of mollicutes, biochemical studies of the pathogen, development of suitable detection tcchniques and initiating budwood certification programmes. However, the studies on fruit plant viruses are comparatively time consuming and hence only a few researchers prefer to work with these viruses, with the result not much work has been done in this direction in India. More scientists therefore should be encouraged to come forward to deal with these difficult problems to gear up the fruit industry on a sound footing in near future.

70

VIRUS AND MYCOPLASMA DISEASES OF FRUIT CRQPS IN INDIA

REFERENCES Ahlawat, Y.S. 1987. 'Association of mycoplasma-like bodies with citrus rubbery wood disease'. Third Regional Workshop on Mycoplasma. In Plant Diseases Caused by Fastidious Prok4ryotes. (Ed.) S.P. Raychaudhuri. and A.Varma, pp. 105-108. Ahlawat. Y.S. 1987. Psorosis-A disease of citrus in India. Indian Phytopath. 42: 21-25. Ahlawat, Y.S. and Ohingra, K.L. 1973. Dodder transmissionn of some temperate fruit tree viruses. Indian Phytopath. 26 : 748-749. Ahlawat, Y.S. and Sardar, K.K. 1976. Lemon crinkly leaf virus in India. Indian Hort. 33: 168-171. Ahlawat, Y.S., Chenulu, V.V. and Varma, A. 1984. 'X' disease-a potential threat to Slone fruit cultivation in India'. Proceedings of the National Seminar of Mycoplasma Infection in Animals, Men and Plants. CSAV, Mathura, pp. 143-146. Ahlawat, Y.S., Nariani, T.K. and Sardar, K.K. 1979. Leathery leaf: A new virus disease of citrus.lndum Phytopath. 32 : 198-201. Ahlawat, Y.S., Payak, M.M. and Thimmalachar. 1989. Control of citrus greening disease in India. Curro Sci. 58 : 921-922. Balaraman, K. and Ramakrishnan, K. 1978. Cross-protection of acid lime with mild strains of tristeza. Indian 1. agric. Sci. 48 : 741-746. Beakbane, A.B. and Thompson, E.C. 1945. Abnormal lignification in the wood of some apple trees. Nature. Lond. 156: 145-146. Beesley, J.E .• Orpin, A. and Adlam. C. 1982. A comparison of immunoferritin, immunoenzyme and goldlabelled protein - A method for the localization of capsular antigen on frozen thin sections of the bacterium, Pasteurella haemolytica. Histochem. 1.14: 803-810. Bar-Joseph, M., Lobenstein, G. and Cohen, J. 1970. Pariial purification of virus-like particles associated with citrus tristeza disease. Phytopathology. 60·: 75-78. Bar-Joseph, M., Garnsey. S.M .• Gonzalves. D., Gonzalves. Moskeritz., M.M., Purciful, D.E., Cleark, M.F. and Loebenstein. G. 1979. The use of enzyme-linked imrnunosorbent assay for detection of citrus tristeza virus. Phytopathology. 69: 109-194. Bar-Joseph, M .• Gumph, OJ., Doddas, J.A., Rosner, A.,Rosner and Guizberg, I. 1985. A simple purification method for citrus tristeza virus and estimation of its genome size. Phytopathology. 75: 195-198. Berg, L.A. and Bustamante, M.C. 1974. Heallreatment and meristem culture for the production of virusfree bananas. Phytopathology. 64 : 320-322. , I Bodine, E.W. 1942. AntagOnism between strains of the peach mosaic virus in western Colorado. Phytopathology. 32 : I (Ahstr). Boyle, 1.S., Moore, J.D. and Keitt, G. W. 1954. Cucumber as a host plant in stone fruit virus research. Phytopathology, 44 : 303-312. Cadman. C.H. and Lister, R.M.1961. Relationship between tomato ring-spot and peach yellow bud mosaic viruses. Phytopathology. 51 : 29-31. Campbell. A.1. 1962. Apple virus inacllvation by heat therapy and tip propagation. Nature. 195: 520. Capoor. S. P. and Rao, O. G. 1967. 'Tristeza virus infection of citrus in India '. Proceedings of International Symposium on Subtropical_and Tropical Horticulturel. Horticultural Society, India. Chamberlain. E. E.. Arkinson. 1. O. and Hunter, J. A. 1964. Cross-protection between strains of apple mosaic virus. N. Z. 1. agric. Res. 7 : 480-490. Cheema. S. S .• Kapur. S. P. and Chohan. 1. S. 1982. Evaluation of rough lemon strains and other rootstocks against greening disease of citrus. Scientia lIorl. 18 : 71-75. Childs, 1. F. L..Norman. G. G. and Eichhorn, 1. L. 1958. A colour test for exocortis infection in Poncirus trifoliala. Phytopathology. 48 : 426-432. Christie. R .G. and Edwardom, J .R. 1977. Light and electron microscopy of plant virus inclusions. Glonogr. Ser. 9. Fla. Qgric. Exp. Stn .• 155 pp. Clark, M. P. and Adams, A. N. 1977. Characteristics of the microplate method of enzyme-linked immunosorhent assay for the detection of plant virues. 1. gen. Virol. 34: 475-483. Cochran. L. C. 1954. 'The origin and interaction of forms of the peach mosaic virus'. Report of 8th International Botany Congress. Paris. pp. 202-204. Costa, A. S. and Muller. G. W. 1980. Tristeza control by cross-protection: A U.S.-Brazillian cooperative success. PI. Dis. Reptr 64 : 538-641. Cropley. R) 960. Serological detection of a virus in cherry trees with a leaf-roll disease. Nature. Lond. 188: 875-876. Derrick. K. S. 1973, Quantitative assay fOf plant viruses using' serologicali y specific electron microscopy. Virology 56: 652-653. Dhingra, K. L. and !{aychaudhuTl, S. P. 1970. Sound cultrual measures can control virus disease of

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apples. Indian Hort. 14 : 3-6. Dhingra, K. L. and Ahlawat, Y. S. 1979.Some additional viral diseases of temperate fruit trees in India. Indian J. Hort. 36: 198-202. Dias, H. F. 1963. Host range and properties of grapevine fan-leaf and grapevine yellow mosaic viruses. Ann. appl. Bioi. 51 : 85-95. Dodds, J. A. and Bar-Joseph, M. 1983. Double stranded RNA from plants infected with closteroviruses. Phytopathology, 73 : 419-423. Ellenberger, C. E. 1962. Dual infection test with three viruses causing leaf symptoms in plum. J. hart. Sci. 37 : 285-290. Fraser, L. R. and Daljit Singh. 1969. 'Reaction of Indian citrus varieties to greening virus '. Proceedings of First International Citrus Symposium. University of California, Riverside, Vpl.l ,pp.141-144. Fraser, L. R., Long, Kand Cox, I. 1968. 'Stem.pitting of grapefruit-field protection by use of mild virus strains'. Proceedings of 4th Conference of Intemational Organization ofOtrus Virologists. pp. 2731. University of Florida, Gianesville, Rorida. Fud1-Allah, A., Calavan, E. C. and Igwegbe, E.C.KI971.Culture of a mycoplama-like organism associated with stubborn disease of citrus. Phytopathology, 61 : 1321 (Abstr). Fudl-AlIah, A. ,Sims, I. 1. and Calavan, E. C. 1974. Indexing of exocortis virus infected citron by using thin-layer chromatography. Pl. Dis. Reptr. 58: 82·83. Garger ,1. S., Turpen, T., Carrington, 1. C., Morris, T. 1., Dodlls, A. 1. and Grill, K. L. 1983. Rapid detection of plant RNA viruses by dot-blot hybridization. PLMol . Biot. Reptr 1 : 21-25. Garnsey, S. M., Gonsalves, D. and Purciful;'D. E. 1979. Rapid diagnosis of citrus tri,steza virus infections by sodium doecyl sulfate SDS immunodiffusion procedures. Phytopathology, 69 : 88·95. Garnsey,~. M., Christie,R. G., Derrick, K. S. ~d Bar-Ioseph,M. 1980. 'Detection of citrus tristeza virus. II. Light and electron microscopy of inclusions and viral particles'. Proceedings of 8th Conference of International Organization of Citrus Virologists. pp. 9-16. Grant, T. 1. and Costa, A. S. 1951. Amild strain of the tristeza virus of citrus. PhYlopalhology, 41; 114122. Hopkins, D. L. 1977. Disease caused by leafhopper-borne rickettSia-like bacteria.Ann. Rev Phytopath. 17: 277-294. Howell, W. E. and Mink, G. I. 1984. Control of natural spread of cheny rugose mosaic disease by a symptomless strain of prunus necrotic ring-spot virus. Phytopathology, 74 : 1139 (Abstr). lones, O. P. and Vine, S. 1. 1968. The culture of goosebeny shoot tips for ehminating viruse.s. J, hart, Sci. 43 : 289-292 Kishi, K and Tanake, S. 1964. Studies on indicator plants for citrus viruses. II. Mechanical transmission of the virus causing satsuma dwarf to sesarne (Sesamun indicum L.). Ann Phylopat h, Soc Japan 29: 142-148. Koizumi, M. 1984. Elimination oftatler leaf citranage stunt virus from satsuma mandarin by shoot· tip grafting following pre-heat treatment'. Proceedings of 9th Conference of International Organization of Citrus Virologists. University of California, Riverside, pp. :n9-233. Kumar, D. 1976 F1uorscent antibody technique for detection of plantpathogens. In Physiology o/M iero· organisms. (Ed.) K.S.Bilgrami. Today and Tomorrow Pub!., New Delhi, pr. 427-436. Kumar, D., Ghosh, S. K. ,Raychaudhuri, S. P., Nariani, T. K and Varma, A. 1975. Fluorescent antibody test for detection of greening mycoplasma.(:,urr. Sci. 44 : 170-171. Kurs!ak,.E., Tyssen, P. and Kurstak, C. !977. Immunoperoxides technique in diagnostic virology and research: Principles and application. In Comparative Diagnosis a/Viral Disease. (Ed.) E. Kuratak and C. Kurstak. Academic Press, New York, pp. 404-448. Lindner, R. C., Kirkpatrick, H. C. and Week, T. E. 1950. A simple staining technique for detecting virus diseases in some woody plant. Science 112 : 119-120. Lister, R. M. ,Bancroft, J. B. and Nadakarukren, M. J. 1965. Some sap transmissible ViruSes from apple. Phytopathology, 55 : 856. Marathe, T. S., Summanwar, A. S. and Ram, R. D. 1982. New additional hosts of Penlalonia n1gronervosa Coq. Curro Sci 51 : 435-436. Marenaud, C. and Bernhard, R. 1968. Cross-protection and interference with stone fruit viruses. Taqungs ber. DI, Akad. Landwirl, 97 : 143-153. Maule, A. I., Hull, R. and Dawson, J. 1983. The application of spot hybridization to the detection of DNA and RNA viruses in plan~ tissues. J viral. Methods 6; 215-224. Miller, R. W. and Belkengren, R. O. 1963. Elimmation of yellow edge, cTinkle and vem banding viruses and certain other virus complexes from strawbernes by excision and cultunng of apical mcnstems, PI. Dis. Reptr 47; 298-300. Milne. R. G. and Luisonl, E. 1975. Rapid high resolution immune electron of microscopy of plant viruses. Virology 68: 270-274.

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Mircetich, S. M. ,Lowe, S. K, Miller, W. 1. and Nyland, G. 1976. Etiology of almond leaf scorch disease and transmission of the causal agent. Phytopathology, 66: 17-24. Mitra, G. C. 1982. Tissue culture of citrus for producing clonal virus-free plants. In Problems o/Citrus Diseases in Inciia. (Ed.) S. P. Raychaudhuri and Y. S. Ahlawat. Surabhi Printers, New Delhi Muller, G. W. and Costa, A. S. 1977. Tristeza control in Brazil by pre-immunization with mild strains. Proc.lnJ. Soc. Citriculture 3: 868-872. Mullin, R. H., Smith, S. H., Frazier, N. W., Schlegel, D. E. and McCall, S. R. 1974. Meristem culture frees strawberries of mild yellow edge, pallidosis and mottle disease. Phytopathology, 64: 1425-1439. Nagaich, B. B. and Vashishth, K. S. 1962. On the occurrence of virus disease of temperate fruits in India. Inciian Phytopath. 15 : 222-224. Naidu, R. and Ramakrishnan, K. 1977. 'Reaction of citrus rootstocks and scions against tristeza strains.' Proceedings of International Symposium on .Citricultrue at Bangalore, pp. 46-47. Naidu, R. and Govindu, H. C. 1981. Association of bacteria-like organism with citrus greening in' India.ClUr. Sci. 50 : 242-224. Nariani, T. K. and Raychaudhuri, S. P. 1971. A long-range citrus bud wood certification progranune for India.lnciian J. Hort. 28 : 144-116 Nariani, T. K., Ghosh, S.K. and Dinesh Kumar. 1973. Tolerance of greening disease to certain citrus species. ClUr. Sci. 42 : 513-514. Nariani, T. K., Ghosh, S. K., 'Dinesh Kumar, Raychaudhuri) S. P. and Viswanath, S. M. 1975. Detection and possibilities of therapeutic control of the greening disease of citrus caused by mycoplasma. Proc. nat. Sci. Acad. 41 (B) : 334-339. Nauer, E. M., ROlstacher, C. N. and Labanauskas, C. K. 1968. Growmg citrus in modified U.c. potting mixture. Calif. Citrograph. 53 : 456-461. Navarro, L . 1981. Citrus shoot·tip grafting in vitro (STG) and its application: A review. Proc. illl. Soc. Citricultrue 1 : 452-456. Navarro, L. ,Rositacher, C. N. and Murashlge, T. 1974. Improvement of shoot-tip in viJrofor virus-free citrus. J. Am. Soc. hort. Sci. 100: 471-489. Noel, M. C. ,Kerlan, C. ,Gamier, M. and Dunez, 1. 1978. Possible use of lnunune-electron microscopy (IEM) for the detection of plum·pox virus in fruit trees. Ann. Phytopalh. 10 : 336-341. Olson, E. 0.1956. Mild and severe strain of the tristeza virus in Texas citrus. Phylopalhology, 46: 336. Owens, R. A. and Diener, T. O. 1981. Sensitive and rapid diagnosis of potato spindle tuberviroid disease by l1ucleic aCid hybridization. SCience 213 : 670-672. Padma, R., Sununanwar, A. S. and Chandra, K. L. 1976. Auorescent antibody staining for detection of coconut root wilt antigen. ClUr. Sci. 45 : 300·301. Paulsen, A. Q. and Fulton, R. W. 1969. Purification, serological relationships and some characteristics of plum-line pattern virus. Ann. appl. Bioi. 63: 233-240. Posnette, A. F. and Cropely, R. 1956. Apple mosaic viruses-host reactions and strain interference. J. horl. Sci. 31 : 19-133. Putz, C. 1971. Obtention de framboisiers (var. Bois Baine) asans virus par la technique des cultures de meristems. Ann. Phylopath. 3: 493-501. Ram, R. D. and Summanwar, A. S. 1984. Colocasia esculenta (L.) Schott., a reservoir of bunchy top disease of banana. Curr. Sci. 53 : 145-146.• Raychaudhuri, S. P. and Mishra, M. D. 1966. 'Application of tissue culture techniques in the study of plant viruses'. Proceedings of first Summer School on Plant Virology. ICAR, p. 46. Raychaudhuri, S. P.,Nariani, T .K. and Ahlawat, Y. S. 1977. Dleback ofcitrus in India. Proc.lnt. Soc. Cilricu/lure 3: 914·918. Regenmortel, M. H. V. Van and Engelbrecht, D. F. 1962. The rapid diagnOSIs ofnecrouc rillg-spot virus infection of stone fruits by serological means. S. Afr. J. agric. Sci. 5: 607-613. ROlstac!Ier, C. N. 1976. 'Detection of citrus Viruses by graft transmission: a review'. Proceedings of7th Conference of International Organization of Citrus Virologists. Riverside, Ca., pp. 175-184. Roistacher, C. N. 1977. Elimination of Citrus pathogens in propagaLlve budwood. I. Budwood selection, indexing and thermotherapy. Proc.lnl. Soc. Cilrtcu/lure 1 : 133-136. Roistacher, C. N. and Calavan, E. C. 1965. 'Cross-protection studies with strain of concave gum, and PSOroSIS viruses'. Proceedings of 3rd Conference of International Organization of Citrus Virologists. pp. 154-161 Roistacher, C. N. and Calavan, E. C. 1972. 'Heat tolerance of preconditioned citrus budwood for virus inactivation'. Proceedings of 5th Conference of International Organizallon of Citrus Virologists. Rosenberger, D. A. and Jonei, A. L. 1977. Symptom remission'in X·diseared peach trees as affected date, method and rate of application of oxytetracycline·HCL. Phytopathology, 67: 277·282. Saglio, P., Lafleche, D., Bomssol, C. and.Bove,).M. 1971.lsolementet culture in vitro des mycoplasmes assocles as 'stubborn' diS agrumes etleurobservation an m~croscope electronique. C r. A cad. Sci.

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Paris (Series D) 272: 1387-1390. Schwarz, R. E.1965. A fluorescent substance present in tissues of greening affected sweet orange. S. Afr. J. agTlc. SCI. 8 : I J77- J J79. Semancilk, J. Sand Wcathers, L. G.1970. Properties of the infectious fonns of exoconis VlruS_ Phytopathology, 60 : 732-736. Sequelfa, O. A De. 1%7. Purification and serology of an apple mosaic virus. Virology 31: 341-322. Sequeira, O. A. De and Lister, R. M. 1969. Applicaoli ity of latex flocculation serologicaltesllng to apple viruses. Phytopathology, 59 : 572-574. Shanna, S, B, and Swarup, G. 1982, The citrus nematode Tylenchulus semipenetranS. In Problems of Citrus Diseases in/ndia (Ed.) S, p, Raychaudhuri and y, S, Ahlawat, Surabhi Printers, New Delhi, Singh, S, ],' Sastry, K,S,M, and Sastry, K. S, 1975. 'Little leaf 'disease of grapevine from India, Curro SCI 44: 26-28. Smha, R, C. 1979. Chemotherapy of mycoplasmal plant diseases. The Mycoplasma. Vol 3. Academic Press Inc., London, pp. 309-355. Summanwar, A. S. and Marathe, T. S, 1982. DiagnostIc technique for the iletection of bunchy top and infectiOUs chloroSIS In hanana suckers. Curro SCI. 51 : 47-49. Tanaka, H. 1972. Mechamcal transmission of vIruses of satsuma dwarf from citrus to citrus. Ann, Phytopath Soc. Japan 38 : 156-160. Tanaka, H. and 1m ada, J. 1974. 'Mechanical transmission of viruses of satsuma dwarf, citrus mosaic. navel infectiOUs plants'. Proceedings of 6th Conference of International Organization of Citrus Virologists. Universay of Californta, DiviSIon of Agricultural Sciences_ Richmond. Thind, S. S., Kapur, S. P. and SOhl, II. S. 1987. 'Effect of chemo-trunk injection on the levels of various element in the greemng infected sweet orange trees'. Fifth National Citrus Semmar. AAU, lorha!. Tomllnson,J. A., Falthfull, E. M. and Ward, C. M. 1976. Chemical suppression of the symptoms oftwo VIruS dIseases. Ann appl Bioi. 84: 31-41. Tremame,J. H. ,Allen, W. R. and Willison, R. S. 19(>4. Serological detectIOn and differentiation of prune dwarf and necrotic ring-spot viruses In prunus tissue extracts. Phytopathology, 54 : 995-998. Tsuchizaki, T. , Sasaki, A. and Saito, Y. 1978. Purification of CitruS uisleza virus from diseased citrus fruits and the detection of the virus In citrus lIssues by fluorescent antibody technique. Phytopathology, 68: 139-142. Walkey, D.G.A. 1978.ln-vllTomethods forvlrus eliminatIon. In Fronllers in Plant TISsue Culture (Ed.) T.A. Thrope. University of Calgary Press, Canada, pp. 245-254. Weiss, E. 1968. ComparalivemcLaboll sm of rickellsla and other host-dependent bacteria. Erste Ableiling Originale 206 : 292-298. Welsh, M.F. and May, 1. 1973a. Suppression of the symptoms of apple leaf pucker disease in an occurrence-pattern that indicates virus Interaction. Can. J. PI. Sci. 53 : 137-145. Welsh, M.F. and May, J. 19730. Suppression of the symptoms of Stayman apple blotch apparently' by virus inactivalton. Can. J PI. Sci. 53 : 565-570_ White, B.A. and Bancarft, F.C. 1982. Cytoplasmic dot hybndization. J. bioi. Chern. 257: 8569-8572. Yarwood, C,E. and Sylvester, E.S. 1959. The half-leaf concept of longevity of plant pathogens. PI. Dis. Replr 43 : 125-129. Yeh, S.D. and Gonsalves, D. 1984. Evaluation of induced mutants of papaya ring-spot virus for control by cross-protection. Phytopathology, 74: 1086-:091. Yora, K., Doi, Y., Raychaudhuri, S.P. and Ahlawat, Y.S. 1977. Infectious variegation of citrus in India. Calif. Cilrograph. 62 : 342. Zeuler, F.W., Edwardson, 1.R. and Purcifull, D.E. 1968. Ultra-microscopic differences in inclusion of papaya mosaic virus, papaya ring-spot virus correlated with differential aphid transmission. Phytopathology, 58 : 332-335.

VIRUS DISEASES OF 1ROPICAL AND SUB-TROPICAL FRUITS

Plate 2. Symptoms of greening disease on mosambi in glasshouse inoculated plant. Left is healthy.

Plate 3. Elrog citron showing epinasLY due to exocorLis infection.

25

26

VIRUS AND MYCOPLASMA DISEASES OF FRUIT CROPS IN INDIA

Plate 4. Sweet orange tree showing scaling or' bark due to psorosis infection.

symptoms on their mature leaves (Ahlawat, unpublished). Psorosis-A and ringspot diseases are now considered to be synonymous. Pruning and removal of affected trees are the only control measures. At the initial stages treatment of about 15 cm bark scraping around the lesion and treating the cut site with 1% potassium permanganate or other surface disinfectant has been recommended to avoid quick deterioration on the trees (Fawcett. 1936).

Blind pocket. This disease is known to occur in California (Klotz. 1961), Florida (Pratt, 1958). Brazil (Rossetti and Salibe. 1962). Chile {Sanchez-Arellano and Weathers, 1971)andin Mediterranean basin (Boveand Vogel. 1961). The leaf symptoms caused by this virus are similar to that of psorosis-A. It has two forms, one plain blind pocket in bark and wood and the other with concavities wilh psorosis-like eruptions. This eruptive form differ from the concave gum disease. on the basis of the type of concavities. It has narrower, more abruptly depressed with two sides coming together at an acute angle at the bottom and al the top. The tissues in the concavities are impregnated with gum which can come out to the surface from these pockets. No effective treatment is known for this form of psorosis. . Concave gum. The disease s.hows typical symptoms of psorosis-A on the young leaves. In addition to this, oak-le"fpatLem on leaves is the most characteristic symptom of concave gum disease which differentiates it from psorosis-A. It is the most distinguished symptom. Concavities of various sizes are formed on the trunk and larger limbs (Klotz, 1961; Zanardi el al .. 1967). These concavities can arrest the growth of wood tissues in locallzed regions. S9melimes bark cracks and