Effects of water stress on water use efficiency of different varieties of common bean (Phaseolus Vulgaris L.)

Abstract

Increasing water use efficiency (WUE), which is defined as the biomass increase per unit of water transpired, is a promising avenue for crop yield improvement, especially in drought-prone environments. The present study tested whether significant inter-varietal variation exists for WUE in common bean (Phaseolus vulgaris L.) under well-watered and water-stressed conditions. Four varieties of common bean ('Cordoba', 'Nerina', 'Top Crop' and 'Wade') were grown in pots within a rainsheltered plant house. Two water treatments were imposed by maintaining plants at 75% (well-watered) and 45% (water-stressed) of field capacity (FC). Transpiration and biomass accumulation were measured by daily weighing and destructive sampling respectively. Biomass accumulation was linearly related to cumulative transpiration in all variety x water combinations. When averaged across all varieties, mean seasonal water use efficiency (WUEm) under water stress (4.025±0.102 gkg-1) was significantly higher than under well-watered conditions (3.532±0.068 gkg-1). Within a given water regime, there was significant inter-varietal variation of WUEm. However, the ranking of varietal WUEm differed with water regimes. 'Wade' had the highest WUEm at 75% FC while 'Nerina' had the highest WUEm at 45% FC. Periodic WUE (WUEp) was significantly higher during the initial 13-day period. Following a subsequent decline, a significant increase in WUE was observed during the pod-filling period. WUEp had significant linear relationships with relative growth rate and net assimilation rate. However, no significant relationship was found between WUE and specific leaf area. It is recommended that the significant varietal variation in WUE present in common bean germplasm be used in breeding for drought tolerance. However, varietal screening should be done under both well-watered and water-stressed conditions to ensure a variety which would perform well under fluctuating seasonal environments.