Experiments were conducted in 1986, 1987, and 1988 to quantify differences between multi-adversity resistant (MAR) and non-MAR cottons and within MAR germplasm for drought tolerance and water use efficiency, and to determine the effect of water stress on lint yield, earliness, and fiber quality traits. Split-plot experiments were conducted in Lufkin sandy loam soil at College Station, with irrigation treatments as whole plots and cultivars as sub-plots, with five replications. In 1986, the irrigated treatment received 5 supplemental irrigations totaling 15 inches of water from June 30 to July 30, with approximately 3-acre inches applied per irrigation. The non-irrigated treatment received less than 0.05 inches of rainfall during the supplemental irrigation period. In 1987, 1.7 inches of rainfall occurred during the stress period, from June 18 to August 27. Six supplemental irrigations totaling 14 inches were applied in 1987 to the nonstress treatment. In 1988, the irrigated treatment received 7 supplemental irrigations totaling 14 inches. Rain during the stress period, June 6 to August 24, amounted to 3.2 inches. An intermediate irrigation treatment was added in 1988 and received 8.5 inches of water from 3 irrigations. Eight of the ten cultivars and strains included in the 1986 and 1987 experiments were from the MAR program and represented hybrid pools MAR-1, MAR-2, and MAR-4. The two non-MAR cultivars were Lankart 57 and Lockett 4789-A. The 1988 experiment included eleven cultivars and strains representing the MAR-2, MAR-4, and MAR-5 hybrid pools, and the non-MAR cultivar Lankart LX571. The traits measured were: daily blooms, cumulative blooms, gin turnout, lint percentage, and boll size. Canopy temperature was measured during the stress period at four dates using an infrared thermometer. The experiments were sequentially harvested at two dates to determine earliness, and total lint yield. Also, fiber quality traits were determined.

The analysis of variance indicated significant differences between years and irrigation treatments and among cultivars for all traits studied. Significant interactions between years and cultivars, and between years and irrigation were obtained for some of the traits. Canopy temperature of the non-irrigated plots was consistently 5 C higher than the irrigated plots with significant differences among cultivars in both treatments.

Averaged over 1986 and 1987 and over cultivars, mid-season water stress caused a significant reduction in lint yield of 48%. Average lint yield was 386 lb/acre for the non-irrigated treatment and 741 lb for the irrigated treatment. There were significant differences in lint yield among cultivars under both irrigation and nonirrigation. The MAR strain CABUICS-2-1-83 and Tamcot CD3H produced the highest yield under both irrigated and non-irrigated treatments, while Lockett 4789-A and Lankart 57 produced the lowest yields. In 1988, lint yield was reduced 38% due to water stress. Average lint yield was 347 lb/acre for the nonirrigated, 461 lb for the intermediate irrigation, and 563 lb for the full irrigation treatment. The new MAR-5 strains CABCHUS-2-86 and CABUCD3H-1-86 produced the highest yields under both irrigation and non-irrigation, followed by the MAR-4 Taincot CD3H and Tamcot CAB-CS. The non-MAR Lankart LX571 produced the lowest yield. The non-irrigated treatments were 24% earlier in maturity than the irrigated treatment. Differential response of cultivars to earliness was more pronounced under irrigation than under water stress. Gin turnout and lint percent were reduced by 3.8% and 3%, respectively, under water stress.

Mid-season water stress had a significant effect on fiber quality. Averaged over both 1986 and 1987 and over cultivars, fiber quality was reduced under nonirrigation; fiber length was reduced by 3.8%, uniformity by 1.2%, strength by 9%, and micronaire was reduced by 13.8%. Averaged over the 1988 cultivars, fiber length was reduced by 7%; fiber length was 1.00 inch for the non-irrigated treatment, 1.01 inches for the intermediate, and 1.07 inches for the full irrigation. Fiber strength was reduced by 8.7%; from 24.9 g/tex for the full irrigation to 22.8 g/tex for the non-irrigated treatment. Micronaire was 9.9% higher for the non-irrigated treatment than the full irrigation. Fiber length and strength were more affected by water stress, than were fiber uniformity, elongation, or micronaire.

The results clearly demonstrated the steady and progressive genetic gains in lint yield under both non-irrigation and irrigation treatments from MAR-1 progressing to the MAR-5 hybrid pools. The increment increases in yield under stress or drought conditions paralleled the increases in levels of resistance to plant pathogens and insects, and to the improvement of fiber quality in the MAR germplasm.