Relationship between yield and some yield components in cowpea varieties infected with two cowpea potyviruses

Abstract

Bean common mosaic virus–blackeye cowpea strain (BCMV-BlC) and cowpea aphid-borne mosaic virus (CABMV) belonging to the genus potyvirus are cosmopolitan and economically important pathogens of cowpea. This study analysed the linear relationship between yield and some yield related characters (numbers of pods per plant, number of seeds per pod, pod growth rate, etc) in 15 cowpea lines infected with BCMV-BlC and CABMV. Isolates of the viruses were mechanically inoculated into the cowpea lines; as a result of the effect of viruses, the cowpea lines were categorized as highly resistant, tolerant, susceptible and highly susceptible. The linear associations between yield and other characters in resistant and tolerant varieties were similar to the associations in susceptible and highly susceptible varieties. The similarity in the correlation coefficient regardless of the susceptibility status was caused by systemic spread of infections in susceptible cowpea varieties such that organs were uniformly reduced while there was minimal reduction in tolerant and no reduction in highly resistant varieties. Pod growth rate correlated (p > 0.05) positively and highly with the yield in seven susceptible varieties and in 5 of the 8 resistant varieties infected by CABMV and BCMV-BlC and the relationship between disease severity and yield showed that as disease severity increased cowpea yield decreased. BCMV-BlC reduced the seed yield between 62 to 87% and CABMV between 54 to 87% in some cowpea varieties. Keywords : cowpea, potyvirus , virus infection, correlation, plant disease Global Journal of Pure and Applied Sciences Vol. 12(1) 2006: 11-17