Effect of soil moisture deficit on photosynthesis and leaf water potential of field grown beans (phaseolus vulqaris l.)

Abstract

A study was conducted during dry periods of 1987 and 1988 at the University of Nairobi"s faculty of Agriculture farm, Kabete to investigate effects of soil moisture deficits on plant water status, photosynthesis, transpiration, stomatal conductance and biomass accumulation of two bean cultivars. The cultivars " Mwezi moja" and'" Rose coco" GLP-I004 and GLP-2 respectively) have been recommended for growing in low and high rainfall areas of Kenya respectively. Watering treatments were imposed during flowering and pod filling stages using a line source sprinkler irrigation system. Photosynthesis was measured using infrared gas analyser system which also monitored stomatal conductance and transpiration rat.e concu'rrently. Leaf water potential was used as a inde>:of plant water status and was measured using a pressure chamber. Results showed that although "Mwezi moja" generally had lower leaf water potential than "Rose coco", its stomatal conductance ,transpiration rate and net photosynthetic rate were consistently higher. It also outyielded Rose coco in all the watering levels having more pods per plant and seeds per pod. This study indicated that there were differences in the two varieties in their response to water stress. If such differences were to be true for other cultivars not included in this study, they could be used in developing beans more adapted to marginal rainfall areas.