Response of Cowpea (Vigna unguiculata L.) Genotypes to Wicth Weed (Alectra vogelii Benth) Infection

A greenhouse pot experiment was conducted at the University of Zimbabwe to screen six cowpea varieties for resistance to Alectra vogelii infection. Emergence of A. vogelii was first detected 55 days after crop emergence. A. vogelii emergence was not significantly (P > 0.05) influenced by cowpea genotype. No differences (P > 0.05) in cowpea parameters that were measured were observed among the cowpea genotypes. However, A. vogelii infection significantly (P < 0.05) reduced cowpea shoot biomass and pod number by 57 % and 98 %, respectively. Infected cowpeas failed to produce any pods at all with the exception of cowpea cultivar C/83/4/6 and C/85/6/4. A similar trend of results was observed with grain yield. Root biomass was not significantly influenced by A. vogelii infection. A. vogelii infected cowpeas had significantly (P < 0.05) higher root /shoot ratio compared to uninfected plants. Based on results on A. vogelii emergence and cowpea parameters collected in this study, it can be concluded that all the cowpea genotypes evaluated are susceptible to A. vogelii infection. However, it can also be concluded that the two pre-released varieties C/83/4/6 and C/85/6/4 are moderately susceptible because they were able to produce grain and should therefore be further evaluated under field conditions.