Exotic Cottons as Genetic Sources for Drought Resistance

As irrigation water becomes more limited and energy costs increase on the Southern Great Plains, more cotton (Gossypium hirsutum L.) acreage will be diverted to dryland production. Because water is the most limiting resource for cotton production in this region, production will be positively related to changes which increase the water supply or make more efficient use of water. The purpose of this study was to evaluate plant (shoot) dry matter accumulation in photoperiodic (exotic) cotton strains under irrigated (water optimal) and dryland (water stressed) field conditions, to estimate their water-use efficiency under dryland, and to determine the relationship between field growth parameters, laboratory evaluations of heat tolerance, and greenhouse estimates of root growth. Fifteen photoperiodic strains and one commerciacl ultivar were planted in irrigated and dryland field tests at Big Spring, Texas and in acrylic tubes in the greenhouse at Temple, Texas. In the Big Spring test, dry weight harvests from both the irrigated and the dryland plots were made at 44, 58, 72, and 86 days after planting (DAP). Soil-water use was measured with a neutron probe in the dryland plots, and leaf discs were taken from both the irrigated and the dryland tests to measure heat tolerance. In them Temple test, shoot dry weight, leaf area, taproot length, and the number of major root laterals were measured 35 DAP. Analyses of variance and regression analyses were used to evaluate the data. Significant variability was demonstrated among entries for shoot dry weights under both irrigated and dryland conditions, for water-use efficiency in the dryland test, for heat tolerance at Big Spring, and for root growth at Temple. The number of lateral roots measured in the greenhouse was positively associated with shoot dry weights in the dryland plots, but not in the irrigated plots. Root morphology and root growth potentials appear to be important traits in the adaptation of cotton to conditions where limited soil-water availability is a major constraint on plant growth.