CONTRIBUTION OF BEAN MORPHOLOGICAL-CHARACTERISTICS TO WEED SUPPRESSION

Weed control has a high labor requirement in small-scale bean (Phaseolus vulgaris L.) production systems in eastern Africa, and productivity of these systems often is constrained by labor availability at weeding times. This study was conducted to determine which morphological characteristics of bean contribute to weed suppression and to assess the feasibility of breeding genotypes for improved ability to suppress weeds. Morphological characteristics and grain yield of 16 to 20 bean genotypes, and weed biomass weight at harvest, were measured over three seasons. Mean weed biomass at time of bean harvest ranged from 55 to 120 g m-2 for the 15 genotypes evaluated for three seasons. The ability to suppress weeds was found to be independent of bean growth habit, but was related to leaf size, leaf area index, and plant growth rate. Leaf size and leaf area index accounted for 73% of the variation among genotypes for weed biomass at the time of bean harvest. These traits were related positively to bean seed yield. Inclusion of large leaf size and high leaf area index as criteria for selecting high-yielding genotypes with improved ability to suppress weeds should be feasible.