Genetic markers associated with Striga Gesnerioides resistance and seed sizes in cowpea [Vigna Unguiculata (L.) Walp.] Inbred lines

Abstract

Production of cowpea is severely hampered by different races of the parasitic weed, Striga gesnerioides. Cultivation of Striga-resistant cowpea is the most reliable protocol to effectively combat the parasite. The current study reported the identification of genetic markers associated with multi-race-Striga resistance and seed size across the genome of cowpea RIL populations. The landrace GH3684 from Ghana was tested for resistance against all known races of Striga gesnerioides in West Africa. Pot experiments were used to test for resistance in each line against Striga populations collected from Northern Ghana (GH) and Nigeria (SG3). Seed size was measured in field trials. SSR and SNP markers were identified and used for phylogenetic analysis and genetic mapping. A genetic linkage map was constructed with QTL IciMapping. Segregation of SSR-1 marker with known association with the Striga resistance gene rsg3 was 100 % consistent with the cowpea phenotypes in SG3. This study indicated that the SG3 resistance gene is located at 12.60 cM away from that of the GH race. On the whole, 70 % of the inbred lines of cowpea were resistant to Striga in Ghana and the lines designated UCC-11, UCC-24, UCC-32, UCC-122, UCC-221, UCC-241, UCC-328 (best RIL candidates for release) and GH3684 were immune to all 7 known races of Striga in West Africa. SARC-LO2 had resistance to four races of Striga (SG2, SG4z, SG5 and SG6). The low genetic diversity and polymorphism information content suggest close genetic relatedness within the RIL population. One and five SNP marker(s) were found to be associated with cowpea seed size and Striga resistance respectively.