Screening of Cherries for Resistance to Leaf Spot, Blumeriella jaapii M. Schuster Federal Centre for Breeding Research on Cultivated Plants, Institute for Fruit Breeding, D-01326 Dresden, Germany

K.R. Tobutt Horticulture Research International East Malling, West Malling, Kent ME19 6BJ, United Kingdom

Keywords: Prunus cerasus, P. avium, Prunus spp., Blumeriella jaapii, leaf spot resistance Abstract An artificial inoculation test method was established in the laboratory to evaluate resistance of cherry genotypes to the leaf spot fungus, Blumeriella jaapii. The reaction type to leaf spot of 52 sour cherry cultivars/clones, 7 sweet cherry cultivars and 11 Prunus species was evaluated. In result 10 sour cherry cultivars/clones showed a resistant reaction type to leaf spot. All tested sweet cherry cultivars were susceptible. The tested Prunus species, P. canescens, P. incisa, P. kurilensis, P. maackii, P. nipponica, P. sargentii, P. serrulata ssp. spontanea, P. subhirtella showed a resistant reaction type to the leaf spot fungus. The species P. dawyckensis was susceptible. INTRODUCTION Cherry leaf spot, caused by the fungus Blumeriella jaapii (Rehm) v. Arx. (syn. Coccomyces hiemalis Higgins), is one of the most serious fungal diseases of sweet and sour cherries. The disease mainly affects the leaves. Diseased leaves drop prematurely, and strongly affected trees may be defoliated by mid-summer. Infection by leaf spot fungus reduces tree vigour and winter-hardiness of buds and wood. Little information exists about the resistance of common sweet and sour cherry cultivars and wild cherry species. Leaf spot is common in cherry growing areas in North America and Europe. In Europe it was reported first in the middle of the 20th century. In the past only a few reports have been published about leaf diseases in nurseries and young plantings. The perfect stage of the leaf spot fungus was detected first in the Netherlands (Roosje, 1964), Poland (Burkowicz, 1964), Hungary (Kaszonyi, 1966) and Germany (Kennel, 1968) (Burth et al., 1970). Nowadays, the fungus has spread all over the cherry growing areas of Europe. MATERIAL AND METHODS Response to leaf spot inoculation was evaluated on 52 sour cherry cultivars, 7 sweet cherry cultivars and 11 wild cherry species from the Genebank of the Fruit Breeding Institute Dresden-Pillnitz. Young leaves from genotypes grafted on rootstocks Piku 1 or Piku 3 (grown in greenhouse) were used for the leaf tests. Leaves or leaf parts were placed in Petri dishes on filter paper soaked with 1% solution of sucrose. The inoculations used conidial suspensions of leaf spot fungus, 1x 106 conidia/ml, prepared from dried naturally infected sweet and sour cherry leaves. Therefore, strongly infected leaves were collected in the cherry orchard in Dresden-Pillnitz in August 2001 and 2002. In 2002 and 2003 screening

for resistance was carried out in the lab in the form of a test on leaves or leaf parts. The reaction type was characterised according to the following scale after 12 days. Reaction type: 0 no symptoms, green leaf 1 scattered small pigmented lesions, chlorotic or necrotic points 2 larger lesions, partly with arial mycelium and stunted sporulating lesions 3 2 to 10 sporulating lesions 4 11 or more sporulating lesions (modified after Wharton et al., 2003) RESULTS AND DISCUSSION In a first step, an artificial inoculation test method was established in the laboratory. In the screening tests, ten sour cherry cultivars showed a resistant reaction type to leaf spot (reaction type 0-2). Forty-two sour cherries and all tested sweet cherry cultivars were susceptible (reaction type 3-4). The tested Prunus species, P. canescens, P. incisa, P. kurilensis, P. maackii, P. nipponica, P. sargentii, P. serrulata var. spontanea and P. subhirtella 'Rendula Rosea' showed a resistant reaction type to the leaf spot fungus. The species P. dawyckensis was susceptible. See Tables 1-3 and Figure 1. The investigations show that the artificial inoculation of leaves in the lab is a quick and easy screening method to assess leaf spot resistance. The results of the leaf tests have to be confirmed under field conditions in subsequent years. The sour cherry cultivars 'Morina', 'Köröser Gierstädt', 'Hartai' and 'Karneol' which have a resistant reaction type (0-2) to leaf spot can be valuable material for use in the breeding of sour cherries resistant to B. jaapii. The tetraploid cultivars 'Almaz' and 'Wishnja' are interspecific hybrids with a low fertility. Shukov et al. (1988) and Wharton et al. (2003) reported the high resistance of 'Almaz'. The best resistance reaction was shown on the investigated cherry wild species. These diploid genotypes are a good pool for genetic studies of leaf spot resistance and possible sources of resistance genes for introgressing into sweet cherry. ACKNOWLEDGEMENTS This research was supported by Deutscher Akademischer Austauschdienst (DAAD) and British Council. Literature Cited Burkowicz, A., 1965. Blumeriella jaapii (Rehm) v. Arx on cultivated stone fruits in Poland. Phytopathologische Zeitschrift 51: 419-424. Burth, U. and Ramson A. 1970. Hauptfruchtform der Sprühfelckenkrankheit der Kirsche auch in der DDR. Dt. Pflanzenschutzdienst (Berlin) 24: 132. Kaszonyi, S., 1966. Life cycle of Blumeriella jaapii (Rehm) v. Arx infecting stone fruits. Acta Phytopath. Aca. Sci. Hungaricae 1: 93-100. Kennel, W., 1968. Ein Beitrag zur Sprühfleckenkrankheit der Kirschen. Erwerbsobstbau 10: 232-235. Roosje G.S., 1964. The perfect stage of Phloeosporella padi, the causal fungus of cherry leaf spot, in the Netherlands. Neth. J. Plant Path. 70: 183-184. Shukov O.S. and Charitonoba E.N. 1988. Sour cherry breeding. Agropromizdat, Moskow

Wharton, P.S., Iezzoni A. and Jones A.L. 2003. Screening cherry germ plasm for resistance to leaf spot. Plant Disease 87: 471-477. Tables Table 1: Results of screening detached leaves for resistance to leaf spot – sour cherry cultivars/clones cultivar/clone Achat (Pi-Sa 5,55) Almaz* Ciganus 59 Csengödi Debreceni bötermö Dropia Erdi nagy gymöstesü Eugenie Imperatrice Fanal Favorit Ferracida Gerema Haaks Dunkelsaftige Hartaer Hartai Jade (Pi-Sa 19,130) Kantorjanosi Karneol Kistiewa Korai Pipacsmeggy Korall Köröser Gierstädt Korund Lara Leitzkauer Leopolds Kirsche Ludwigs Frühe Mari timpurii Meteor korai Morina Nana Oblacinskaja Paljus Pamjatch Vavilova Pandy 2 Pieraszt Pitic de Dragoslaven Pitic de Jasi * interspecific hybrid

reaction type 4 0 2 2 3 3 3 4 4 4 3 4 4 3 1 3 3 1 4 1 4 2 3 4 4 4 3 3 3 2 4 3 2 3 3 4 3 3

continue Table 1 (continued): cultivar/clone Röhrigs Weichsel Rubellit (Pi-Sa 11,134) Safir Schattenmorelle Schirpotreb Schöne von Montreuil Schwäbische Weinweichsel Studenskaja Tarina Topas Tschernokorka Turgenjevka Ujfehertoi fürtös Wishnja*

reaction type 3 4 3 4 4 3 4 4 3 4 4 4 4 1

* interspecific hybrid

Table 2: Results of screening detached leaves for resistance to leaf spot – sweet cherry cultivars cultivar Krupnoplodnaja Lapins Namati Napoleon Naprumi Sunburst Vinka

reaction type 4 3 4 4 4 4 4

Table 3: Results of screening detached leaves for resistance to leaf spot – wild cherry species species Prunus canescens P. dawyckensis P. incisa P. incisa 'Incana' P. kurilensis P. maackii P. nipponica P. sargentii 'clone 34' P. sargentii 'Rancho' P. serrulata ssp. spontanea P. subhirtella 'Pendula Rosea'

reaction type 1 4 1 1 1 1 1 1 1 1 1

Figure

Resistant genotypes (reaction type 1)

P. incisa ‘Incana‘

Sour cherry cv. ‘Wishnja‘

Susceptible genotypes (reaction type 4)

Sour cherry cv. ‘Kistiewa‘

Sour cherry cv. ‘Ujfehertoi fürtös‘

Figure 1: Reaction type of resistant and susceptible cherry genotypes