Insufficient or unevenly distributed rainfall often limits genetic yield potential of non-irrigated cotton. Six cotton genotypes (cultivars and breeding lines) were evaluated over a two-year period in the field under irrigated and non-irrigated treatments to determine differences in lint yield, earliness, and drought resistance. Four genotypes, Tamcot SP37H, Tamcot CD3H, MAR-CABU'US-2-1-83, and MAR-MACAOS-3-84 were developed in the multi-adversity resistance (MAR) cotton improvement program. The two non-MAR cultivars were Deltapine 41 and Paymaster 303. The irrigated treatment received five supplemental furrow irrigations to maintain near-optimum water status throughout the flowering period. The non-irrigated treatment received only natural rainfall. At crop maturity, entire plots were sequentially harvested and lint yield and earliness determined. An index was developed to characterize the relative drought resistance of each genotype.

For each year, significant differences were observed among genotypes for lint yield in the non-irrigated treatment only, with MAR-CABU'CS-2-1-83 and Tamcot CD3H producing the highest yields. Genotypes also differed in crop maturity with the four MAR genotypes being significantly earlier than Deltapine 41 under both water regimes. Correlation coefficients obtained between lint yield and earliness within and between treatments detected no significant relationships between the two traits, suggesting that drought escape due to earliness was not a major contributor to increased lint yields. Drought susceptibility indices based on minimization of yield reduction due to water deficits indicated that MAR-CABUICS-2-1-83 and Tamcot CD3H possessed higher levels of drought resistance than did Deltapine 41, Paymaster 303, or Tamcot SP37H.

After analyzing lint yield data and drought susceptibility indices, Tamcot CD3H and Paymaster 303 were evaluated in the greenhouse to determine differences among a drought resistant and susceptible genotype for root traits, total water transpired, and water use efficiency. Plants were grown in metal trays under two water regimes. The non-stressed treatment was maintained at near field capacity for the length of the experiment, while the water stressed treatment received no additional water 30 days after planting.

The two cultivars differed for root traits, total water transpired and water use efficiency. Tamcot CD3H, a drought resistant cultivar, had a higher percentage of lateral roots in the total root system, greater root water storage capacity, transpired less water, and had greater water use efficiency than did Paymaster 303.Results suggested that the increased yield and drought resistance of Tamcot CD3H may have resulted from one or a combination of the measured plant traits. These studies indicate that currently available cotton germplasm possesses traits which allow plants to minimize or delay the effects of a limited water supply.