Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/1997
Publication Date: N/A
Interpretive Summary: The yield potential of both upland and Pima cotton are adversely affected by the high temperatures occurring in the desert southwest of the United States. Recent studies have shown heat resistance is available in Pima cotton, and that it is related to higher photosynthetic rates, smaller leaf sizes, and to an increased cooling capacity due to high stomatal conductance. In the present study we compared the stomatal conductance, photosynthetic rate, and leaf size of the high yielding, heat adapted upland cultivar, Deltapine 90, with those of the heat resistant Pima S-6 cultivar. Under field conditions, the upland cultivar Deltapine 90 had stomatal conductance and photosynthetic rates that were superior to the heat resistant Pima S-6. Stomatal conductance also appeared to be more responsive to temperature in the Deltapine 90 cultivar than in Pima S-6. Studies of a cross between Deltapine 90 and Pima S-7 showed that stomatal conductance was clearly under genetic control and heritable. Although upland and Pima cultivars derive from two different species, causing problems in hybridizing the two, interspecific hybridization appears to be a viable strategy for increasing the heat resistance in Pima cottons.
Technical Abstract: Both Gossypium barbadense L. (Pima) and Gossypium hirsutum L. (upland) cotton species are grown in the southwestern United States, where lint yields are adversely affected by high temperatures. Recent studies have shown that increases in lint yield and heat resistance in Pima cultivars are tightly coupled to increases in stomatal conductance and photosynthetic rate, and to decreases in leaf area. In the present study, Pima S-6 and Pima S-7 were compared to the upland cultivar Deltapine 90 to determine if physiological and morphological parameters related to heat resistance can be extrapolated to upland cotton. In the field, the higher yielding Deltapine 90 showed 25-35% higher stomatal conductance, 35-50% higher photosynthetic rate, and 45% smaller leaf area than Pima S-6. In gas exchange experiments that prevented sun-tracking in the upland cultivar, Deltapine 90 and Pima S-6 had comparable photosynthetic rates that remained nearly constant over a 25-35 deg. C temperature range. Over the same temperature range, Deltapine 90 displayed a higher stomatal conductance and steeper response curve than did Pima S-6. Population means and variances of F1 and F2 progeny from a cross of Deltapine 90 and Pima S-7 showed a clear genetic component to stomatal conductance. These results indicate that the upland cultivar Deltapine 90 possesses levels of stomatal conductance and photosynthesis superior to those found in Pima cultivars. Interspecific hybridization may be a viable strategy in improving heat resistance in Pima cotton.