New sources of aphids [Aphis craccivora (Koch)] resistance in cowpea germplasm using phenotypic and molecular marker approaches

This study sought to identify new sources of resistance to cowpea aphids (CPA) using molecular and phenotypic approaches and the inheritance pattern. Sixty cowpea genotypes were phenotyped for resistance to CPA using insect proof cages and further confirmed using markers linked to aphid resistance. Result revealed that among the cowpea genotypes, TVu 2897 and TVNu 1158 supported lowest number of aphids and plant damage scores. The seedlings of these genotypes also had high level of survival rates and were completely healthy with normal growth. This indicates that these genotypes are resistant to aphid attacks. However, the resistance in TVNu 1158 did not seem strong compared to the genotype TVU 2897 that was confirmed to be resistant to multiple aphid biotypes. The mechanism of resistance in TVu 2897 and TVNu 1158 were expressed as a hypersensitive response at the site of infestation on the leaves. The other genotypes especially Aloka local and keffi local supported the highest number of aphids, damage score and low level of survival rate, suggesting that they are susceptible to aphid attack. The cowpea genotype IT84S-224-6 previously reported to be resistant to aphids supported high number of aphids and was marked by stunted growth and high mortality rate. Molecular and phenotypic screening revealed that TVu-2876 has a strong resistance to cowpea aphid and should be a good source of resistance gene that can be used in breeding to develop new aphid resistant cowpea cultivars. Although, the results of phenotypic tests and molecular marker detection agreed in most cases, molecular markers detection was found more reliable in identifying genotypes for resistance to CPA. The segregation in F₂ and BC1 populations derived from the cross between TVNu 2876 and Keffi local indicated that resistance to cowpea aphids in TVu-2876 is controlled by a single dominant gene. Allelism test revealed that resistance gene in TVNu 2876 is non-allelic with the gene that confers resistance in SARC 1-57-2 and TVNu 1158.