Agricultural Science Research Journal 4(2); pp. 30- 38, February 2014 Available online at http://www.resjournals.com/ARJ ISSN: 2026 – 6332 ©2014 International Research Journals

Full Length Research Paper

Agro-phenotypic characterization of sweet potato (Ipomoea batatas L.) genotypes using factor and cluster analyses Norman PE*, Beah AA, Samba JA, Tucker MJ, Benya MT, Fomba SN Njala Agricultural Research Centre (NARC), PMB 540, Freetown, Sierra Leone. *

Corresponding author email: [email protected] Abstract

An agro-phenotypic characterization study was conducted at the Njala Agricultural Research Centre (NARC) experimental site, Sierra Leone. The aim of the study was to evaluate the level of diversity within sweet potato germplasm using factor and cluster analyses. A total of 17 genotypes including six introduced and eleven local entries were grown in a randomized complete block design with three replications in 2012 and 2013. Twenty-eight morphological traits measured from the genotypes were analysed using factor analysis (FA) and hierarchical cluster analysis (HCA). Factor analysis loaded five factors which explained 72.79% of the total phenotypic variation in the dependence structure. Other factors (>6) explained the rest of the genetic variation and may not be important in sweet potato breeding programmes. Unweighted pair-group method using an arithmetic average (UPGMA) revealed eight groups at distance coefficient of 0.80. This study revealed that wide genetic variation exists in sweet potato genotypes grown in Sierra Leone which could be used to breed for high yield and other desirable food and market traits. Findings would also be useful for conservation planning of sweet potato using molecular techniques to confirm the variation observed. Key words: Sweet potato, agro-phenotypic, characterization, factor, cluster, analyses

INTRODUCTION Sweet potato (Ipomoea batatas (L.) Lam) is one of the most important root crops in the world, especially in subSaharan Africa (SSA). The area under cultivation of sweet potato in SSA covers approximately 3 million hectares with an estimated annual production of 13 million tons (Low and van Jaarswels, 2008). Sweet potato is highly productive and requires little demand of input and labour for its cultivation. In addition, it can also thrive well in unfavourable growth conditions. There is increasing awareness of sweet potato as a cheap and valuable source of vitamin A which plays an important role in preventing blindness and malnutrition in children. It is also a good source of calcium and ascorbic acid (vitamin C) and provides more edible energy than all other staple foods. These characteristics altogether make this crop suitable and attractive to farmers with little resources (Low et al., 2009).

In Sierra Leone, sweet potato ranks third after rice and cassava, and is grown throughout the country for food and cash (MAFFS/NARCC, 2005) with an estimated production of 187,000 metric tons from 2010-2011 (IMF, 2011). Both the young leaves and vine tips serve as vegetables and are consumed by most households. Due to its wide adaptation to different environments and short duration it serves as a major source of staple food (MAFFS/NARCC, 2005). There is also the possibility of sweet potato to be processed into flour for industrial use and other value-added foods. Despite the growing importance of sweet potato in Sierra Leone, there is little or no information on the level of morphological diversity of sweet potato for its efficient utilization in the sweet potato improvement program. This dearth of information had contributed to the slow progress in the crop’s improvement at Njala Agricultural

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Table 1. Identification of 17 sweet potato genotypes and its geographical origin of germplasm characterized in the study Genotype Clone 1 Clone 2 Clone 3 Clone 4 Clone 5 Clone 6 Clone 8 SLIPOT 2* SLIPOT 3* SLIPOT 4* Kabbia Carome Ex-Igbariam MGQ Shaba TIB Tiebele-2

Origin Sierra Leone Sierra Leone Sierra Leone Sierra Leone Sierra Leone Sierra Leone Sierra Leone Sierra Leone Sierra Leone Sierra Leone Sierra Leone Burkina Faso IITA, Nigeria IITA, Nigeria IITA, Nigeria Burkina Faso Burkina Faso

Accession No. 04/01 04/02 04/03 04/04 04/05 04/06 04/08 82/123W 82/144 84/16 04/09 440136 Ex-Igbariam MGQ Shaba 440060 440002

*SLIPOT=Sierra Leone Potato

Research Centre (NARC), one of the nine centres of Sierra Leone Agricultural Research Institute (SLARI), mandated to carry-out research on root, tuber and grain legume crops. Morphological characterization of plants is vitally imperative for the detection of desirable peculiar traits, identification of duplicate accessions and structuring of population for conservation (Reed et al., 2004; Manamela, 2009). The process saves storage space and makes selection by plant breeders simple. Selection of genotypes by phenotypic traits has contributed to the domestication of plants with desired traits that meet farmers’ demands (Gepts, 2004). Morphological diversity is evaluated through measurement of variation in phenotypic characters including both above and below ground traits (Rao, 2004). Against this background, and given the potential of sweet potato in alleviating hunger and malnutrition, morphological characterization of current sweet potato germplasm will serve as a good guide for the genetic development, conservation, collection and utilization of germplasm. This is a prerequisite for the rational use and conservation of available genetic resource (Fraleigh, 2006). The aim of this study was therefore to evaluate the level of diversity within germplasm using factor and cluster analyses. Materials and methods A total of 17 sweet potato accessions comprising six introduced genotypes: three from IITA, Nigeria, three

from Burkina Faso and 11 genotypes from Sierra Leone were screened and characterized at Njala Agricultural Research Centre (NARC) during 2012 and 2013 cropping seasons (Table 1). Njala is situated between latitude 80°6' N and longitude 12°06' W with an elevation of 50 m above sea level. The soils at the trial site belong to the Njala series (orthoxic palehumult) that is largely gravely clay-loam texture, slightly acidic with pH ranging between 5.5 and 6.0, and of predominantly secondary bush vegetation (MAFFS/NARCC, 2005). The experiment was laid out in a randomised complete block design (RCBD) with three replicates. The planting distance was 0.3 m x 1 m within and between rows giving a population of 33,3333 plantsha-1. Twenty eight morphological traits collected during the study were scored using the CIP/AVRDC/IBPGR (1991) descriptors for sweet potato with slight modification (Table 2). Thirteen above ground traits were scored within three months after planting (MAP) in the field. All traits recorded were the average of 10 plants randomly selected and tagged. At harvest (5 MAP), 15 underground storage root and quality traits were also assessed using the same descriptor. Multivariate analyses of the 17 x 28 data matrix comprising factor analysis (FA) and hierarchical cluster analysis (HCA) were done in Genstat 12.1 (Payne et al., 2009) for Windows statistical software package to determine variation within the various accessions. The data were first rank transformed in order to in order to obtain uniform residuals. In the FA, eigenvalues and load coefficient values were generated from the data set. The principal components (PCs) that had eigenvalues > 2.0

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Table 2. Morphological traits measured in 17 sweet potato (Ipomoea batatas) accessions. The traits and measurement methods were based on the International Board for Plant Genetic Resources descriptor list (CIP/AVRDC/IBPGR, 1991) CIP code

Trait acronym

Trait/ descriptor

Score code – descriptor state

4.1.2

PLTT

Plant type

4.1.3 4.1.4.1

GC VIL

Ground cover Vine internode length

4.1.5.1

PVC

Predominant colour

4.1.5.2

SVC

Secondary vine colour

4.1.7.1

GOL

4.1.7.2 4.1.7.3 4.1.7.4

LLT LLN SCLL

4.1.10.1

MLC

General outline of the leaf Leaf lobes type Leaf lobe number Shape of central leaf lobe Mature leaf colour

3–erect (250 cm) 3–low (90%) 1–very short (12 cm) 1–green; 2–green with few purple spots; 3–green with many purple spots; 4–green with many dark purple spots; 5–mostly purple; 6–mostly dark purple; 7–totally purple; 8–totally dark purple 0–absent; 1–green base; 2–green tip; 3–green nodes; 4–purple base; 5 – purple tip; 6– purple nodes 1–rounded; 2–reniform; 3–cordate; 4–triangular; 5–hastate; 6–lobed; 7–almost divided

4.1.10.2

ILC

Immature leaf colour

4.1.11

PL

Petiole length

4.1.12

PP

Petiole pigmentation

4.2.1

SRS

Storage root shape

4.2.4.1

PSC

4.2.5.1

PFC

4.2.5.2

SFC

Predominant skin colour Predominant flesh colour Secondary flesh colour

6.1.3.2 6.1.3.2 6.1.3.2 6.2.1.1

TY MKTY NMKTY SRDMC

6.2.1.2

SBDMC

6.2.1.3 6.2.9.3

HI TBSRF

6.2.9.4

SBSRF

6.2.9.5

CTSRF

6.2.9.6 8.1.1

PLOSS SWP

vine

Total yield Marketable yield Non-marketable yield Storage root dry matter content Storage biomass dry matter content Harvest index Texture of boiled storage root flesh Sweetness of boiled storage root flesh Cooking time of boiled storage root flesh Peel loss Sweet potato weevil

0–no lateral lobes; 1–very slight; 3–slight; 5–moderate; 7–deep; 9–very deep Direct measurement (1, 3, 5, 7, 9) 0–absent; 1–toothed; 2–triangular; 3–semi-circular; 4–semi-elliptic; 5–elliptic; 6– lanceolate; 7–oblanceolate; 8–linear (broad); 9–linear (narrow) 1–yellow-green; 2–green; 3–green with purple edge; 4–greyish-green; 5–green with purple veins on upper surface; 6–slightly purple; 7–mostly purple; 8–green upper, purple lower; 9–purple both surfaces 1–yellow-green; 2–green; 3–green with purple edge; 4–greyish-green; 5–green with purple veins on upper surface; 6–slightly purple; 7–mostly purple; 8–green upper, purple lower; 9–purple both surfaces 1–very short (40 cm) 1–green; 2–green with purple near stem; 3–green with purple near leaf; 4–green with purple at both ends; 5–green with purple spots throughout petiole; 6–green with purple stripes; 7–purple with green near leaf; 8–some petiole purple, others green; 9–totally or mostly purple 1–round; 2–round elliptic; 3–elliptic; 4–ovate; 5– obovate; 6–oblong; 7–long oblong; 8– long elliptic; 9–long irregular 1–white; 2–cream; 3–yellow; 4–orange; 5–brownish orange; 6–pink; 7–red; 8–purple red; 9–dark purple 1–white; 2–cream; 3–dark cream; 4–pale yellow; 5–dark yellow; 6–pale orange; 7– intermediate orange; 8–dark orange; 9–strongly pigmented with anthocyanin 0–absent; 1–white; 2–cream; 3–yellow; 4–orange; 5–pink; 6–red; 7–purple-red; 8–purple; 9–dark purple Direct measurement (tha-1) Direct measurement (tha-1) Direct measurement (tha-1) Direct measurement (%) Direct measurement (%) Direct measurement (%) 1–dry; 2–somewhat dry; 3–intermediate; 4–moist; 5–very moist 1–not at all sweet; 2–slightly sweet; 3–mostly sweet; 4–sweet Direct measurement (min) Direct measurement (%) 1–no visible symptom; 2–mild; 3–low; 4–intermediate; 5–high

were selected, and those traits that had load coefficient values > 0.30 were considered as relevant scores for the

PC, which significantly contributed to distinguish between the genotypes (Jeffers, 1967). For comparison between

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accessions, distance coefficients were computed and information summarized in dendrograms using Unweighted Pair Group Method using arithmetic Average (UPGMA) parameters in NTSys-pc. RESULTS Phenotypic variation among genotypes The variation in gross morphology, storage roots, quality and biotic stress traits are presented in Table 3. Of the 17 genotypes studied, three genotypes (clones 3, 8 and MGQ) had almost divided leaf shape; seven genotypes (clone 5, SLIPOTS 2, 3, 4, Ex-Igbariam, Shaba and Tiebele-2) had cordate leaf shape; six genotypes (clones 1, 4, 6, Kabbia, Carome 440136 and Tib-440060) had lobed leaf shape; and one genotype, clone 2, had hastate leaf shape. Variation in storage root shapes included the following: four genotypes, clones 4, 6, SLIPOT 4 and MGQ, exhibited round storage roots; four genotypes, SLIPOT 2, SLIPOT 3, Kabbia and Shaba had round elliptic storage roots; two genotypes, clone 8 and Tiebele2, had elliptic storage roots; four genotypes, clones 1, 2, 3 and Tib-440060, had ovate storage roots; clone 5 had obovate storage roots; Ex-Igbariam had long irregular or curved storage roots. Variation in predominant flesh colour of storage roots included the following: five genotypes (clone 3, SLIPOT 2, SLIPOT 4, Ex-Igbariam and shaba) had white flesh; two genotypes (clones 1 and 5) had cream flesh; one genotype (SLIPOT 3) had pale yellow flesh; four genotypes (clones 2, 4, 6 and 8) had pale orange flesh; two genotypes (Carome-440136 and MGQ) had intermediate flesh; one genotype, kabbia had strongly pigmented with anthocyanin flesh whereas Tiebele-2 had dark orange flesh. The multivariate analysis based on the 28 morphological traits revealed considerable diversity among the 17 accessions of sweet potato evaluated in this study. Each of the first 10 principal components had eigen-value greater than 0.6 and together explained 92.99% of the total variance in the data set (Table 4). The higher the eigen-value of a component, the more representative it is of the data. The percent of variance explained is dependent on how well all the components summarize the data. The factor analysis: The five principal component eigenvalues that were greater than 2.0 (Table 4) suggest the use of five factors in the factor analysis (Norman et al., 2011). Factor loadings with coefficients greater than equal to 0.25 (ignoring the sign) were considered important and emboldened. These large and moderate loadings indicated how the traits were related to the factors (Manly, 1994). The contributions by the communalities were low with 28 traits exhibiting lower communality over the specificity (Table 4). Factor 1 was high-loaded with: general outline of leaf (-0.3974), leaf

number (-0.3017), leaf lobe types (-0.4230), peel loss (0.3296), shape of central leaf lobe (-0.4176) and vine internode length (0.2700). Factor 2 was high-loaded with: mature leaf colour (0.2590), plant type (0.3968), petiole length (0.3176), sweetness of boiled storage root flesh (0.4032), severity of sweet potato weevil on storage root (0.3838) and storage root shape (0.3885). Factor 3 was high-loaded with: non- marketable root yield (-0.3524), predominant flesh colour (-0.3546), petiole pigmentation (-0.4130), predominant skin colour (-0.3388) and predominant vine colour (-0.4081). Factor 4 was highloaded with cooking time of boiled storage root flesh (0.3319), ground cover (0.3649), mature leaf colour (0.2898), storage biomass dry matter content (0.2707), secondary flesh colour (0.3721), secondary vine colour (0.4133) and texture of boiled storage root flesh (0.2650). Factor 5 was high-loaded with harvest index (0.4427), marketable yield (0.4902), texture of boiled storage root flesh (0.3115) and total yield (0.5261). In this study, factor 1 did not account for most of the variation in the traits. Thus, the factors were rotated to further explore the variables. Generally, all the traits measured were useful in determining variation in the sweet potato accessions. The five factors considered distinguished the traits into groups. The highest weightings by factor 5 were given to marketable yield (0.4902) and total yield (0.5261). These traits were not only highly positively related (r=0.919) (Table 6), but also served as important components in distinguishing between the accessions. Results of the rotated factors generally indicated that variation in all traits was largely influenced by specificity compared to communality. For instance, the variation in cooking time of boiled storage root flesh (CTSRF) was explained by 18.78% contribution from communality of which factor 4 (11.02%) contributed most compared with factors 1 (4.38%), 2 (2.60%), 3 (0.69%) and 5 (0.10%). The specificity accounted for 81.22% and so on. Cluster analysis: The dendrogram of the hierarchical cluster analysis (HCA) separated the 17 genotypes into different clusters with Euclidean distance dissimilarities ranging between 0.6 and 1.0 (Figure 1). At the dissimilarity distance of 0.80, the dendrogram identified eight main clusters. Accessions of cluster 1 (clones 1, 2 and 3) were characterized by green with few purple spots predominant vine colour, very short petiole, ovate storage roots, low to intermediate attack of sweet potato weevil and slightly sweet boiled storage root flesh. Accessions of cluster 2 (Carome 440136 and Tib 440060) were characterized by green with few purple spots predominant vine colour, green base secondary vine colour, lobed general outline of leaf, five deep leaf lobes, lanceolate central leaf lobe, green with purple veins on upper surface immature leaf, short petiole and high (>80%) harvest index. Accessions of cluster 3 (SLIPOTS 2 and 4) were characterized by cordate leaf, yellow-green -1 mature leaf, high marketable roots (>8.0 tha ), high harvest index (76-94%), white storage root flesh, round

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Table 3. Description and photographic display of various above and below ground traits of 17 sweet potato accessions studied in Sierra Leone Genotype Clone 1

Leaf traits

Root traits

Flesh colour

Description Lobed leaf shape, ovate root shape, dark cream flesh colour

Clone 2

Hastate leaf shape, ovate root shape, pale orange flesh colour

Clone 3

Almost divided leaf shape, ovate root shape, white flesh colour

Clone 4

Lobed leaf shape, round root shape, pale orange flesh colour

Clone 5

Cordate leaf shape, obovate root shape, cream flesh colour

Clone 6

Lobed leaf shape, round root shape, pale orange flesh colour

Clone 8

Almost divided leaf shape, elliptic tuber shape, pale orange flesh colour

SLIPOT 2*

Cordate leaf shape, round elliptic, white flesh colour

SLIPOT 3*

Cordate leaf shape, round elliptic, pale yellow flesh colour

SLIPOT 4*

Cordate leaf shape, round root shape, white flesh colour

Kabbia**

Lobed leaf shape, anthocyanin

Carome440136

Lobed leaf shape, long oblong, intermediate orange flesh colour

Ex-Igbariam

Cordate leaf shape, long irregular shape, white flesh colour

MGQ

Almost divided leaf shape, round root shape, intermediate orange flesh colour

Shaba

Cordate leaf shape, round elliptic, white flesh colour

Tib-440060

Lobed leaf shape, ovate root shape, dark yellow flesh colour

Tiebele-2

Cordate leaf shape, elliptic tuber shape, dark orange flesh colour

*=improved released varieties, **=widely grown local variety

round

elliptic,

strongly

pigmented

with

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Table 4. Eigen-value, percentage variation and accumulated variation explained by each component of, the first 10 principal components (PCs) Principal component (PC) 1 2 3 4 5 6 7 8 9 10

Eigen-values 6.590 4.662 3.458 3.057 2.612 1.680 1.366 1.147 0.875 0.738

Variation of each component (%) 23.54 16.65 12.35 10.92 9.33 6.00 4.88 4.10 3.12 2.64

root, low percent peel loss (30.0%), mild attack of sweet potato weevil on storage roots, mostly sweet and somewhat dry boiled storage root flesh. Cluster 4, SLIPOT 3 and Kabbia, exhibited totally dark purple vine, green with purple spots throughout petiole, round elliptic storage roots, dark purple storage root skin and high (40.0%) storage dry matter content.Kabbia had deep leaf lobe, strongly pigmented with anthocyanin and dark purple secondary flesh, whereas SLIPOT 3 exhibited slightleaf lobe and pale yellow predominant root flesh. Accessions of cluster 5 (Clones 4 and 5) were characterized by yellow-green leaf, intermediate petiole (21-30 cm), green with purple near leaf petiole pigmentation, yellow secondary root flesh colour. Clone 4 had lobed leaves, round roots and pale orange flesh whereas clone 5 had cordate leaf, obovate roots and cream root flesh. Cluster 6 comprised of Shaba and ExIgbariam, characterized by total ground cover, intermediate vine internode length, mostly purple vine, cordate leaf, very slight leaf lobes, low attack of sweet potato weevil, mostly sweet and intermediate texture of boiled storage root flesh. Shaba had spreading plants, green with purple near leaf, yields >3.0 tha-1, round elliptic root, white root flesh, while Ex-Igbariam exhibited extremely spreading plant, green with purple petiole at -1 both ends, least yielder of