Phenology and Diurnal Course of Leaf Water Potential of Three Bean Varieties under a Semi-Arid Environment in South-East Kenya
The objectives of this study were to observe the phenology and to investigate the diurnal behaviour of leaf water potential (LWP) in three bean varieties under irrigated and unirrigated treatments with a view to making recommendations on their suitability for the semi-arid environments of Kenya. The field experiments were conducted during the short rainy season of 1993/94 in a typical semi-arid environment at KARIlNRRCIICRISAT Kiboko experimental field station, southeast Kenya. The selected beans were: high-yielding kenyan bean varieties Mwezi moja (MM) and Rose coco (RC) (Phaseolus vulgaris, var. GLP-I004 and var. GLP-2, respectively) and "minor pulse" Tepary beans (TB) tPhaseolus acutifolius A. Gray var, latifolius), possessing a high nutritional value. Under irrigated conditions, the bean varieties took 60 (TB), 65 (MM) and 70 days (RC), after emergence to reach full maturity respectively; water deficit induced false starting of phonological phases of the less adapted Phaseolus vulgaris. Differences in leaf water potential between the treatments were apparent. TB appeared to maintain higher leaf water potential values and showed more pronounced diurnal responses than MM and RC beans in both treatments. This also resulted in less yield reductions during water deficit for Phaseolus acutifolius. The susceptibility of Phaseolus vulgaris to water deficit is also documented by the fact that their LWP decreases more rapidly much earlier in the morning than TB. The short growth cycle of TB together with the maintenance of high leaf water potentials (and good yield performance) even under water deficit could be interpreted to mean that they are more adaptable to the semi-arid environments of Kenya compared to MM and RC beans.