Developing cultivars of the common bean ( Phaseolus vulgaris L.) for southern Africa: bean common mosaic virus resistance, consumer preferences and agronomic requirements

Abstract

The requirements that must be met by bean common mosaic virus (BCMV)-resistant cultivars of the common bean in Zimbabwe, and the feasibility of developing such cultivars, were investigated by a survey among farmers, evaluation of resistant and locally adapted inbred genotypes, and backcrossing to transfer the bc-3 resistance gene to the genetic background of the locally adapted genotypes. Genotypes were evaluated by field trials in a range of environments, by consumer assessment and by measurement of seed size, water absorption capacity (WAC) and cooking time. Backcross generations were evaluated in the field and by measurement of the same seed characters. Most farmers produced beans in monoculture, using bush or semi-climbing cultivars and a single seed type, the most common colour type being cream with red mottles. This is in strong contrast to the production system in many parts of eastern and central Africa, where intercropping, climbing types and seed-type mixtures are common. The BCMV-resistant genotypes had a similar range of flowering dates, maturity dates and canopy heights to locally adapted genotypes, and a similar range of environmental responses with respect to these variables, but were generally small-seeded. Consumers preferred large seeds, and seed colours that were not generally found in the resistant genotypes. However, the bc-3 gene was readily combined with large seed by backcrossing. The resistant genotypes generally had shorter cooking times than the locally adapted genotypes. It is concluded that it will not be difficult to combine BCMV resistance with the other characteristics required of bean cultivars in Zimbabwe, with the possible exception of seed colour, and that the same is probably true for other production regions in southern Africa.