Genetic inheritance of resistance to cowpea aphid-borne mosaic virus in cowpea

Cowpea aphid-borne mosaic virus (CABMV) is a major virus disease in Uganda that causes substantial loss of the cowpea crop especially in growth and yield. The mode of gene action conferring resistance to the virus is not well understood. The objective of the study was to determine the genetic inheritance of resistance in cowpea crosses. Three susceptible (S) cowpea landraces that are commonly grown by farmers were crossed with five introduced resistant cowpea varieties in accordance with a North Carolina mating design II scheme. The F₁, F₂ and BC₁F₁ progenies generated were evaluated in the field together with their parents. They were then infected with two infection methods namely: by spreader-rows of S cultivar (Ebelat) and artificial inoculation of virus extracts. The results obtained showed that general combining ability (GCA) and specific combining ability (SCA) effects were significant, indicating that both additive and non-additive gene effects controlled virus infection. The results further demonstrated that the GCA effects (59.8?%) were more important than SCA effects (40.2?%) in determining virus resistance in the cowpea varieties. Utilisation of good general combiners of the varieties MU-93, IT82D-516-2, SECOW-2W and IT85F-2841 in hybridisation to improve virus resistance in cowpea crosses would be recommended. The result of this study provided an indication that CABMV resistance was conditioned by more than one recessive gene in eight populations, but also revealed resistance to be conditioned by a single recessive gene in the other seven populations. Observation of continuous distribution of progenies for severity data in the F₂ populations also confirmed significance of quantitative inheritance for CABMV resistance. Therefore, the significance of GCA effects suggests that recurrent selection could be applied to accumulate the additive genes for resistance in F₂ populations.