Genetic Relationship between Turgor Maintenance and Growth in Cotton Germplasm1

Abstract

Seventeen photoperiodic sensitive cotton (Gossypium hirsutum L.) stocks were grown for 2 years (1980 and 1981) at Big Spring, Tex. to evaluate the relationship between turgor maintenance and shoot dry matter accumulation (growth). During each year, leaf‐cutter thermocouple psychrometers were used to measure predawn and midday leaf water and osmotic potentials and to estimate turgor pressure at 50 and 80 days after planting (DAP). Shoot dry weights were measured also at 50 and 80 DAP. The 1st year was hot and dry while the 2nd year had about average temperatures and rainfall. Linear regressions between predawn and midday water and turgor potentials were used to estimate turgor maintenance as i) the change in turgor pressure per unit change of water potential (slope) and, ii) the osmotic potential where zero turgor pressure occurred (X intercept). Significant differences did not occur among the stocks for changes in turgor pressure per unit change in water potential (slope), but they did occur among stocks for osmotic potential at zero turgor (πo) all four sampling dates. Analysis over‐all of the sampling dates, identified a consistently low (T178) and high (T292) stock for πo. Linear correlation and regression coefficients between shoot dry weights and πo were negative and statistically significant during the sampling period (80 DAP, 1980) when the plants were water‐stressed. The linear correlation and regression coefficients were negative, but not statistically significant during the other sampling periods (50 DAP, 1980, and 50 and 80 DAP, 1981). Linear correlation coefficients between the change in shoot dry weights between 50 and 80 DAP in 1980 and the change in πo were negative (r = ‐0.82) and statistically significant. These relationships suggesthat if selection pressure is directed towards enhancing osmotic adjustment under water stress, a reduced growth potential may result.