Selection for pod quality, pod yield and disease resistance in climbing snap beans

Abstract

Climbing snap beans have the potential of increasing productivity and competitiveness in domestic and export markets, but suitable varieties with market demanded p od quality characteristics and preferred agronomic traits are not available to smallholder farmers in Kenya and other countries in east, central and west Africa. The objective of the study was to select climbing snap beans with market preferred pod quality characteristics, pod yield and disease resistance from locally developed breeding populations and advanced lines. Twenty F 5.7 lines with type IV growth habit were evaluated at Mwea and Embu during the 2013 long rain and short rain sea sons . Diseases were scored on 1 to 9 disease scale, where scores of 1 - 3 were considered resistant; 4 to 6, intermediate; and 7 to 9, as susceptible. After pod formation, plots were harvested every other day. Pods were graded as extra - fine, fine and bobby using standard commercial criteria. Results showed that there were significant genotypic differences for plant vigour, disease resistance, days to first picking, pod yield, pod length and market grades among the new lines. Plant vigor scores varied from 1 to 7 at Embu, and 1.7 to 3.5 Mwea. Check varieties were the most vigorous lines in both sites but they were not the highest yielders. Anthracnose and angular were the most severe diseases especially at Embu where sprinkler irrigation was used. Except for K SV27 - 69 - 4 - 1 - 2T, all other lines showed resistant reactions to anthracnose and angular leaf spot. Rust incidence was low throughout the season and all genotypes showed resistant reactions. Duration to 50% flowering varied from 43.5 to 52 days in Embu, and 3 1.8 to 48.5 days in Mwea. This may have contributed to differences in days to first picking which varied from 56 to 60 days after planting. Pod yield over 9 harvests in Embu varied from 3,252 to 10,626 kg ha - 1 . The total yield from 18 harvests in Mwea vari ed from 16,214 to 23,724 kg ha - 1 . New lines out - yielded the the checks by 56.6%. The new lines produced an average of 44.1% premium grades. However, this varied with genotypes and was not significantly influenced by number of harvests. The results of this study indicate that new climbing snap bean varieties with market demanded pod characteristics, high yield potential and resistance to major diseases can be developed from the selected lines. Exploitation of the longer harvest period of climbing beans can c ontribute to higher yields and better returns to investment especially for smallholder farmers, and to the overall competitiveness of the snap bean sub-sector