Selection for multiple disease resistance in bush snap bean lines developed in Kenya

Production of snap beans (French beans, Phaseolus vulgaris L.) in Kenya is severely constrained by diseases. Use of fungicides increases cost of production, reduces profitability and competitiveness of snap bean in domestic and export markets. Varieties with multiple disease resistance can reduce costs associated with use of chemicals especially for smallholder farmers. The objective of the study was to select for combined resistance to rust, anthracnose and angular leaf spot, market preferred pod quality characteristics and pod yield from locally developed advanced snap bean lines. About 300 F5 lines selected from 31 populations for combined resistance to rust, angular leaf spot and anthracnose were evaluated at Mwea and Embu during the 2013 long rain and short rain seasons. Diseases were scored on 1 to 9 scale, where lines with score of 1-3 were considered resistant, 4 to 6 intermediate and 7 to 9 susceptible. Plots were harvested three days a week for a period of four weeks and pods graded as extra-fine, fine and bobby using standard commercial criteria. There were no significant differences in anthracnose and rust at both sites, though significant differences were recorded at Mwea. Mean disease scores for angular leaf spot and anthracnose varied from 1-5, while rust mean scores ranged between 1 and 6 at both locations. Four new lines with multiple disease resistance had better pod yield and pod quality compared with existing commercial varieties at both locations were identified. The mean disease score for these lines was 1-3 for the three diseases. These lines had fresh pod yield more than 10,000 kg ha- 1 at both locations compared with an average of 4,000 kg ha-1 realized in farmers’ fields with commercial varieties. None of the commercial check varieties exhibited multiple disease resistance. These results indicate the potential of developing new high yielding snap varieties with multiple disease resistance and good pod quality. New varieties from these lines can increase incomes of smallholder farmers who are constrained by reliance on costly fungicides and enhance competitiveness of local products in export markets.