Seventeen photoperiodic cotton strains were grown for two years at Big Spring, Texas to evaluate the relationship between turgor maintenance arid shoot dry matter accumulation. Leaf cutter psychrometers were used to measure predawn and midday leaf water potential, osmotic potential, and turgor potential at 50 and 80 days after planting (DAP) during each year. Shoot dry weights and leaf areas were also measured at 50 and 80 DAP. The first year (1980) was extremely dry while the second year (1981) had above normal rainfall. Regression between predawn and midday water and turgor potentials were used to estimate the change in turgor per unit charge of water potential (slope) and the osmotic potential where zero turgor potential occurred (X intercept). Analysis of variance was used to determine if entry differences occurred in these traits as well as shoot dry matter accumulation. Regression was used to evaluate the relationships between turgor maintenance and growth.

Significant differences did not occur among the entries for changes in turgor per unit change in water potential (slopes), but significant differences occur red among entries at all four sampling dates for osmotic potential at zero turgor (ão). Analysis over all sampling dates, identified two strains as consistently high (Tl78) and low (T292) for ão. These differences occurred whether or not the plants were undergoing water stress. Correlations between shoot dry weights and ão were negative and highly significant (r = 0.80) during the sampling period (80 DAP, 1980) when the plants were stressed for water. The correlation coefficients were negative, but not significant during the other sampling periods (50 DAP, 1980 and 50 and 80 DAP, 1981). Correlation coefficients between the change in shoot dry, weights in 1980 and the change in ão were negative and highly significant (r = 0.82). These relationships suggest that selection directed towards enhancing the ability of plants to maintain turgor under water deficits will result in reduced growth potential.