Response of Introduced Cowpea Breeding Lines to Aphid Infestation in South Africa.

Production of cowpea (Vigna unguiculata [L.] Walp) in South Africa is limited by lack of improved varieties and quality seeds for planting; therefore, new introductions of cowpea breeding lines were made and evaluated for their adaptation. These introduced breeding lines have not been screened for cowpea aphid resistance in South Africa. The objective was to evaluate the response of  cowpea breeding lines from IITA, Nigeria and Texas A&M University to aphid infestation. Ninety seven elite cowpea breeding lines were evaluated in a field trial (1 row with 0.75 m row spacing; 3 m length) during the 2013-14 growing season at University of Limpopo Experimental Farm, Mankweng, Limpopo Province. The experiment was completely randomized block design with three replications and local line Vita 7 was the control. Three weeks prior to planting test lines, susceptible Vita 7 was planted in areas which would surround test lines to ensure infestation. Eighty six (89%) of the 97 lines exhibited 100% aphid incidence indicating that lines were uniformly infested. Control was susceptible to aphid as indicated by aphid and plant vigor scores. Only 22 lines had aphid score of 1 to 4 (resistant), but 32 lines were medium strength to strong (vigorous). Plant biomass (R² = -0.71), plant height at 3WAI (R² = -0.76), and canopy height at maturity (R² = -0.72) were negatively correlated to aphid score. The results of this study indicate that the breeding lines responded differently to aphid infestation and aphid damage reduced the performance of the lines. Additionally, the identified 22 resistant lines and 32 lines with promising vigor will be subjected to more intensive evaluation to validate the results obtained from this study.