Timing of Environmental Stress Affects Growth, Water Relations and Salt Tolerance of Pinto Bean

THE influence of a cool, humid vs. a hot, dry environment on the growth, water relations, and salt tolerance of pinto bean (Phaseolus vulgaris L.) was determined at several salinity concentrations of the root medium. The effects of changing from the cool, humid to the hot, dry environment for 2 wk during the vegetative and the flowering growth stages were also investigated. Growth and pod yield of bean plants exposed to the hot, dry environment during the vegetative stage were comparable with those of plants continuously exposed to the cool, humid environment. Exposure to the hot, dry environment during flowering, however, reduced yields significantly, but not to levels for plants exposed continuously to the hot, dry environment. This inter-action with environment was the same for all salinity levels. Bean grown in the cool, humid environment tolerated higher salt levels than those predicted from published tolerance data. Transpiration rates changed rapidly in response to environmental changes. Differences in transpiration decreased as salinity increased. Linear relationships were found between the osmotic potential of the root medium and leaf water potential and its components. Stomatal conductance was also found to be linearly related to leaf water potential and its components. Stomatal conductance was higher in the cool, humid than in the hot, dry environment for any value of the root medium osmotic potential.