Introgression Of Cowpea Aphid Resistance Gene Into Susceptible Cowpea [Vigna Unguiculata (L.) Walp] Cultivars Through Marker Assisted Backcrosses

ABSTRACT

Aphid infestation is recognized as one of the major constraints that limit cowpea production in Africa. Host-plant resistance has proven to be the most efficient and sustainable means to controlling aphid infestation and its associated challenges. The objectives of this project were to characterize cowpea varieties using 38 agro-morphological and 20 SSR markers, and also to deploy aphid resistant locus into three locally preferred aphid susceptible cowpea cultivars. A total of 22 cowpea varieties were evaluated in a Randomized Complete Block Design (3 blocks) on the experimental fields of CSIR-CRI, Fumesua in the minor rainy season of Ghana using the IBPGR cowpea descriptor. Characterization results showed a relatively high level of genetic diversity among the varieties which ranged from 1 - 0.007, 1 - 0.001, 0.652 - 0.109 for qualitative, quantitative and molecular markers respectively. Principal component analysis, dissimilarity matrices, principal component biplot, and clustering separated the accessions according to some qualitative and quantitative traits with the aid of Genstat version12.0 and Statistical Package for Social Sciences (SPSS) version 16.0 software. Among the 20 SSR markers screened, 19 primer pairs were polymorphic. One to six alleles per primer were detected with polymorphic information content (PIC) varying from 0.107 (SSR-6608) to 0.656 (SSR-6613) with mean of 0.293 and allele frequency ranging from 0.136 (SSR-6371) to 0.841 (SSR-6608) with mean of 0.445. The SSR marker CP171F/172R successfully distinguished between 5 aphid resistant varieties and 15 aphid susceptible varieties. The aphid resistant locus from a donor (SARC-1-57-2) was then deployed into three locally preferred cultivars (Asontem, Nhyira and Asetenapa) in a marker assisted backcross up to BC2 generation. After genotyping the BC1 individuals, 63 individuals who

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picked up the gene as revealed by the marker were selected to develop 261 BC2 seeds. The characters documented in this research will guide selection in subsequent backcrosses; diversity observed can also be exploited by breeders for forensic identification of cultivars and also used in cowpea improvement programmes. This research has also deployed the aphid resistant locus into three locally preferred cultivars. Successive backcrosses will lead to the complete improvement of the three cultivars.