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Water Relations and Carbon-14 Assimilation of Cotton with Different Leaf Morphology¹

The purpose of this research was to determine the usefulness of simply inherited genetic differences in cotton (Gossypium hirsutum L.) leaf morphology (normal, laciniate, and superokra) as it relates to drought tolerance or water use efficiency. This initial report describes the leaf water potential components, C0₂ fixation rates, and the rate of loss of assimilated ¹⁴C from various source leaves on plants subjected to soil water stress at select growth stages under glasshouse conditions.

No significant genotypic differences were observed in leaf water potential components or in CO₂ fixation rates when the soil water content was near field capacity. Trends did exist for the superokra to be slightly superior to the normaleaf type. Significant differences were observed in both the rate and extent of ¹⁴C loss from different source leaves in the various genotypes. The superokra genotype had the highest activity, whereas the normal leaf genotype was the lowest in activity.

As soil water availability began to affect leaf water status, significant genotypic differences existed in all measured physiological parameters. The superokra genotype was able to maintain a more favorable leaf water status through a combination of higher leaf water potential and lower osmotic potentlal than the normal leaf genotypes. Photosynthetic rates were reduced by water stress in all genotypes; however, the magnitude of the reduction varied significantly among the genotypes reflecting specific differences in turgor pressure. The removal of assimilated ¹⁴C from various source leaves subjected to water stress also exhibited significant genotypic differences both in the rate of removal and in the total amount of assimilate removed during a 24-hour period. As water stress intensified the photosynthetic assimilation of ¹⁴CO₂ was found to be more sensitive than the removal of assimilate from the source leaf.

The results of these experiments indicate a possible advantage of altered leaf morphology when cotton leaves are subjected to soil water stress. The benefits of improved water relations and CO₂ assimilatlon to yield in the altered leaf types of cotton remain to be evaluated.

Key Words: Gossypium hirsutum L. • Normal • Laciniate • Superokra • Leaf water potential • Osmotic potential • Turgor potential

² Associate professor, Dep. of Agronomy, Shiraz Univ., Shiraz, Iran (This research was conducted while on sabbatical leave at Texas Tech Univ.); professor, Plant and SOil Science Dep., Texas Tech Univ.; Lubbock, TX 79409; and Research geneticist USDA-SEA, Rt. 3, Lubbock, TX 79401.

Received for publication May 21, 1979.

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