New Sources of Resistance in Cowpea to the Cowpea Aphid (Aphis Craccivora Koch) (Homoptera: Aphididae)

Abstract

Twenty-two advanced breeding genotypes of cowpea were evaluated for their responses to infes-tation by the cowpea aphid, Aphis craccivora Koch. The aim of the study was to identify geno-type(s) of cowpea resistant to A. craccivora to be used as breeding line(s). Seedling screening technique and aphid growth and reproduction on each genotype were used to classify the geno-types into resistant and susceptible groups. The cowpea genotypes SARC 1-57-2 and SARC 1-91-1 were found to be the most resistant genotypes, whereas five of the genotypes namely, Apag-baala, IT 97K-499-35, IT 98K-506-1, IT 95K-193-2 and Marfo-Tuya were highly susceptible. The high susceptibility of the IITA lines must be a cause for concern, particularly the IT 97K-499-35 line which is known to be resistant to A. craccivora in Nigeria. This suggests the exis-tence of cowpea aphid biotype in northern Ghana which is more virulent than the biotypes in Nigeria. The results support earlier findings of the development of aphid biotypes that are more aggressive and are not controlled by the aphid resistance varieties of cowpea developed by IITA for Nigeria.