Effect of timing of application of gibberellic acid and ethephon on growth, yield and yield components of beans (phaseo/us vulgaris L)

Abstract

Two parallel field experiments were carried out at the Faculty of Agriculture, Field Station farm, University of Nairobi during the short rains of 1997 and repeated during the long rains of 1998, to determine the effects of GA3 and ethephon on the growth, grain yield and yield components of beans (Phaseolus vulgaris L.) variety Mwezi moja. GA3 at 0, 2.5, 5.0 or 7.5 mg/litre was applied to bean plants to run off at 7, 14 and 28 days after emergence (DAE). Ethephon at 0, 100, 200 and 300 mg/litre was also applied at 7, 14 and 28 days after emergence. Application of GA3 increased plant height, leaf area indices, fractional solar radiation interception, root dry mass, shoot dry mass and the total dry mass. GA3 increased grain yield per plant, pods per plant, 100- seed mass and harvest indices. The number of seeds per pod was not affected by GA3 application at all dates. It was concluded that low GA3at 7.5mg/litre could be used to improve the yield of beans. Yield increases was realized most when GA3 was applied at the time of maximum leaf expansion, which is 14 DAE in this study. At all times of application, ethephon reduced plant height. Application of ethephon at 28 DAE reduced the leaf area index, fractional solar radiation interception, shoot dry mass and total dry mass, which were not affected by application at 7 or 14 DAE. All applications of ethephon had no effect on the root dry mass. Application of ethephon at 28 DAE caused most reduction in yield per plant and reduced harvest index. Ethephon application at all dates had no effect on the number of pods per plant, seeds per pod and 100- seed mass, except at 28 DAE, where it reduced the number of pods per plant and 100- seed massThis study recommends that ethephon should not be used to improve the yield of beans.