Physiological and yield responses of sunflower to water stress at flowering

Effects of water stress and its subsequent relief at flowering stage on leaf water potential, stomatal conductance, photosynthetic rate and transpiration rate of two sunflower cultivars (BSH-1 and Surya) were studied under pot conditions in 1987 and 1988 seasons. Leaf area and dry matter accumulation in plant parts one week after recovery from the stress, and seed yield and its components at maturity were also determined. The objective was to compare the responses to water stress of the two cultivars of similar duration but differing in yield potential under non-stress conditions for better understanding of the productivity of the crop in drylands. Physiological responses and relative reductions in seed yield due to the water stress were similar in both the cultivars. Surya produced comparatively higher seed yield under stress probably because of its higher yield potential rather than due to any physiological drought tolerance mechanism. However, the relatively low yielding BSH-1 exhibited significant increase in mean weight per seed in the stress-relieved plants, partially buffering the effect of reduction in number of seeds on seed yield. These results lead to a tentative conclusion that seed yield under water limited environment may be independent of any drought tolerance mechanism in sunflower genotypes of similar duration.