Breeding for resistance to ear rot of maize, caused by Stenocarpella maydis (Berk) Sutton. 2. Inheritance of resistance

The inheritance of resistance to ear rot, caused by Stenocarpella maydis, was investigated using a complete diallel cross of 10 inbred lines, ranging from resistant to susceptible. Parents, F1 crosses and reciprocals were evaluated at each of three localities, representative of different environments within the South African maize production area. Plants were artificially inoculated twice during the vegetative stages of development. Based on the incidence of rotted ears, resistance to S. maydis was found to be controlled by additive gene effects with low dominance and interaction effects. Sufficient GCA and SCA effects existed in the resistant inbred lines to serve as donor parents for the improvement of susceptible germplasm. Inbreds D0620Y and MON1 showed good general combining ability for resistance whereas inbreds B37 and E739 were noted for specific combining ability. Sources of variation that could be employed to breed for improved husk cover and ear declination were identified. However, it was shown that these would not necessarily contribute towards resistance. Genotype × environment effects were pronounced, indicating the necessity to conduct resistance evaluations in a variety of localities.