HERITABILITY AND PHYSIOLOGY OF DROUGHT TOLERANCE IN SORGHUM (SORGHUM BICOLOR (L.) MOENCH).

Abstract

Physiological responses of 12 sorghum (Sorghum bicolor L.) genotypes previously classified as drought resistant and susceptible upon grain yield basis were evaluated under dry and wet moisture treatments at Tucson, Arizona in 1983. In addition, the relationship of these physiological responses and their heritability estimates were also determined. Apparent photosynthesis, transpiration, diffusive resistance, temperature differentials, and leaf temperature were measured under field conditions at three intervals from planting date: 48, 62, and 77 days, respectively. Stomatal density and epicuticular wax content were determined toward the end of the season when full canopy development was reached. Stress significantly affected all characteristics measured for each genotype by a reduction in apparent photosynthesis rates, transpiration, and temperature differentials, and an increase in diffusive resistance, leaf temperature and stomatal density. The wax content response varied among genotypes irrespective of the dry and wet moisture treatments. Except for the wax content and stomatal density, all the other parameters demonstrated a high significant correlation with photosynthesis at .001 level; nevertheless, greater values were observed in the stress treatment. Analysis of variance failed to detect significant differences among the 12 germplasm sources, except for the stomatal density. Multiple regression analysis showed that leaf diffusive resistance was the first variable incorporated for photosynthesis prediction in both the dry and wet treatments. The offspring and mid-parent regression for each characteristic under both treatments provided heritability estimates (h('2) (+OR-) SE), indicating higher heritability values under the dry treatment.