Screening of Cowpea (Vigna unguiculata L.) Germplasm in a Screenhouse for Novel Aphid Resistance

Abstract

Cowpea [Vigna unguiculata (L.) Walp.] is an important nutritional and economic grain legume; however, its productivity in Kenya remains low because of various stresses, including aphid infestation. The use of synthetic insecticides for aphid control negatively affects the environment, thereby limiting continued reliance on them. Introduction of high-yielding and aphid-resistant germplasm could help increase productivity in a sustainable manner. This study aimed to assess the response of 60 cowpea accessions to imposed aphid stress with the goal of identifying resistant accessions. It was conducted using a randomised complete block design with three replications in two trials. Data were recorded on cowpea growth, yield and aphid infestation parameters at various time intervals and subjected to analysis of variance at P = 0.05. Results revealed highly significant (P<0.05) differences for all phenotypic traits assessed. In trial 1, days to 50% flowering ranged from 45 (NA20) to 61 (NA62), and grain yield ranged from 11.3 (NA28) to 1158.8 (MA29) kg/ha; in trial 2, the corresponding ranges were 48 (NA4) to 61 (MA67) days and 15.6 (BS01) to 389.3 (NA57) kg/ha. The grain yield was negatively (P<0.05) correlated with days to 50% flowering, but positively (P<0.05) correlated with leaf length in trials 1 and 2, respectively. There was a significant difference (P<0.05) in aphid population pressure (APP) and aphid damage severity (ADS) at 5 to 21 days after infestation (DAI). At 21 DAI in trial 1, the average number of aphids per plant ranged from 219 (NA71) to 24.5 (MA48), while in trial 2, it ranged from 113.5 (NA20) to 12.2 (MA22). The summarised ADS scores were 4 for 22 accessions and 3 for 38 accessions in trial 1, whereas in trial 2 they were 4 for 2 accessions, 3 for 54 accessions, and 2 for 4 accessions. The accessions with the lowest grain yield loss may be stable against aphids in major cowpea growing regions in Kenya. The four accessions showing great resistance (KK03, MA10, MA22, MA44) to aphid infestation should be evaluated in multiple field sites to confirm their resistance to aphids, followed by deployment to areas prone to high aphid infestation to minimize pesticide reliance and associated negative effects. Furthermore, they should be validated using molecular markers to confirm their resistance genes before incorporating them into farmers’ preferred, but susceptible varieties to boost their resistance to aphids.