Selection for short day adaptation in vegetable runner bean in Kenya

Runner bean (Phaseolus coccineus L.) offers considerable potential as a high value vegetable and grain crop for domestic and export markets in eastern Africa. However, production and utilisation of vegetable runner beans in Kenya is severely constrained by reliance on imported long-day varieties which require additional artificial lighting to trigger flowering and pod formation under tropical short-day conditions. The objective of this study was to select for short-day adaptation, pod quality and yield from four runner bean bulk populations developed from crosses between long-day and short-day parental lines. One hundred thirty-seven vegetable types F6 progenies were evaluated at two locations (Kabete, 1800m and Ol JoroOrok, 2300m) during 2013 long and short rain seasons in Kenya. Data collected was collected on number of racemes per plant (each raceme having 10-20 single flowers), days to 50% flowering, disease resistance and fresh pod yield. The numbers of racemes was counted during the first flush of flowers (85 days after planting) and second flush (110 days). The results showed that there were significant differences (P<0.01) in days to 50% flowering and the number of flowers formed during the 1st and 2nd flush of flowering stage at both sites. The mean number of racemes per plant varied from 0 to 21 at Ol Joro-Orok, and 0 to 7 at Kabete. The numbers of racemes per plant were higher at Ol Joro-Orok than at Kabete during the two flowering stages, suggesting better adaptation of runner bean to cooler, higher altitudes. The new locally bred lines had significantly more racemes (each raceme had 15 single flowers) compared with the long-day parent, White Emergo at both sites. The results suggested that photoperiod sensitivity is heritable and can be exploited in breeding short-day varieties of runner beans. New lines had a mean pod yield of 2,396 kg ha-1, while the longday check variety failed to produce pods. The results indicate that improved vegetable type runner bean varieties which do not require additional lighting can be developed from these lines. This will facilitates local seed production, reduce costs of production and competitiveness of vegetable runner bean in domestic and export markets.