Effect of water stress on physiological attributes and their relationship with growth and yield of wheat cultivars at different stages

The effects of water stress on physiological attributes of drought-sensitive (Kalyansona) and drought-tolerant (C-306) wheat cultivars were studied in a pot experiment. Water stress was imposed by withholding irrigation at boot and anthesis stages. Leaf water potential, leaf osmotic potential and leaf turgor potential (measured with pressure chamber and osmometer), as well as leaf diffusive resistance, leaf transpiration rate and leaf-to-air transpiration gradient (measured with a steady-state porometer) were measured diurnally. Growth and yield parameters were recorded after harvesting of the crop. Triplicate data were analysed using a completely randomized design and correlations amongst these parameters were computed. Water stress was found to reduce diurnal leaf water potential and leaf osmotic potential in both the genotypes but leaf osmotic potential was significantly higher in the drought-tolerant cultivar C-306 than in the drought-sensitive cultivar Kalyansona. Positive turgor was recorded in both the genotypes under water stress and non-stress conditions. Water-stressed plants showed significantly lower turgor potential than control plants. In diurnal observations, water-stressed plants exhibited significantly higher leaf diffusive resistance in both genotypes at both stages. The diffusive resistance of C-306 was predominantly higher than that of Kalyansona. Water stress decreased leaf transpiration rate at both stages but the reduction was higher at the anthesis stage. The leaf-to-air temperature gradient was much higher in C-306 than in Kalyansona at the boot stage but at the anthesis stage genotypic variation was nonsignificant. The capacity to maintain cooler foliage was lower at the anthesis stage than at the boot stage in both the cultivars. Shoot dry weight, number of grains, test weight, grain yield, biological yield and harvest index decreased to a greater extent when water stress was imposed at the anthesis stage, while imposition of water stress at the boot stage caused a greater reduction in plant height and number of tillers. Similarly, water stress caused a smaller reduction in growth, yield and yield attributes in C-306 than in Kalyansona. In general, the correlation coefficient of grain and biological yield with water potential and its components was positive and highly significant. Similarly, turgor potential was also correlated positively and significantly with grain yield at both the stages, but with biological yield it was significant only at the anthesis stage. A negative and significant correlation was obtained for diffusive resistance and leaf-to-air temperature gradient with grain yield at the boot and anthesis stages. The rate of transpiration was also positively and significantly correlated to grain and biological yields at both the stages. Amongst the yield attributes, number of leaves and number of tillers were positively correlated at the anthesis stage, whereas leaf area and shoot dry weight were significantly correlated with grain and biological yields at both the stages.