Simple sequence repeat polymorphism screening for resistance to Cercospora Arachidila in groundnut(Arachis Hypogaea)Genotypes
Kanyika, Chali Ncube Tamara Busisiwe
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Arachis sp. cultivation in Africa is largely by small holder farmers that lack the resources to counteract the negating effects of foliar disease Early Leaf Spot (ELS) caused by Cercospora arachidicola. C. arachidicola causes yield losses which on interaction with other pests and/ or diseases and favourable weather conditions aggravate yield losses in Sub–Saharan Africa. The utilisation of chemical control methods is not economically feasible for the small holder farmer and requires additional skill, a tedious regime for effective application and in addition, is toxic to the environment. Hence, reduced yields impinge on the income and nutrition of third world communities. Resistant genotypes are available but have not been adequately accepted due to limited farmer preferred characteristics and other quality traits. The tediousness of handling a self pollinating species in gene introgression by interspecific hybridisation and the general mode of inheritance to disease resistance complicates the transfer of resistance. Resistance is a low heritability trait governed by quantitatively inherited recessive genes that are controlled by epistatic effects and are closely associated to the environment. Simple Sequence Repeat (SSR) molecular markers are environmentally stable and highly informative. These markers have therefore been identified as useful in hastening breeding programmes in Arachis sp. The overall objective of this study was to identify highly informative SSR markers across 16 genotypes of farmer preferred and other improved African Arachis sp. germplasm traits that may be effectively linked to ELS disease resistance. The markers were graded on a scale of 1–4 according to ease of scoring. A total of 394 showed Polymorphic Information Content (PIC) values ranging from 0.06 to 0.86, giving a total of 1476 at an average of 3.7 alleles per locus and so distinguishing the 16 species. Markers of grade 1–3, high availability and PIC were carried forward to establish a dissimilarity matrix to highlight the most appropriate pair wise combinations for resistance breeding studies. The matrix ranged from the most closely related genotypes 0.34 (MGV5: ICGV 90704) to the most distantly related 0.66 (Chalimbana: 47–10). The mean dissimilarity matrix value was 0.51. A total of 139 (35 percent) polymorphic marker locations were ascertained with reference to pre–existing genome maps for future utilisation in Quantitative Trait Loci mapping. The most informative SSR markers for 16 cultivated Arachis sp. indigenous to Sub–Saharan Africa were compiled. These can be used to improve the efficiency of introgression of ELS resistance into farmer preferred varieties and also other molecular marker assisted crop improvement studies for foliar disease resistance and quality traits of significance to the smallholder farmer in Sub–Saharan Africa.
- Agricultural Sciences