Author
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Snider, John |
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OOSTERHUIS, D - University Of Arkansas |
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Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Book / Chapter Publication Acceptance Date: 1/12/2011 Publication Date: N/A Citation: N/A Interpretive Summary: Cotton originates from hot climates, but does not necessarily yield best at excessively high temperatures, and a negative correlation has been reported between yield and high temperature during early boll development. Although cotton is sensitive to high temperature at all stages of growth, it is particularly sensitive to high temperatures during reproductive development, and environmental stress during floral development represents a major limitation to crop productivity. Because a number of reproductive processes must occur in highly concerted fashion on the day of flowering (from pollination to fertilization) for successful fertilization and seed production to occur, final yield in cotton is strongly influenced high temperatures during the flowering period. Depending upon the duration, timing and severity of heat stress, fertilization could be limited by poor pollen and ovule development, decreased pollen germination, and limited pollen tube growth. Under field conditions, pollen tube growth rate is extremely sensitive to moderately high temperatures, where exposure to moderately high ambient temperatures (34.6°C) results in slower pollen tube growth rates despite no change in pollen germination or ovule fertilization. Heat stress limits fertilization by decreasing photosynthesis, depleting pistil ATP and carbohydrates, increasing oxidative stress in the pistil, and altering pistil calcium concentrations. Having higher pistil concentrations of ATP and calcium is related to genotypic tolerance to high temperature. Furthermore, reproductive thermotolerance in cotton is also associated with having elevated pre-stress antioxidant enzyme activity in both the leaf and the pistil, which is likely a mechanism for coping with rapid temperature fluctuations that occur under field conditions. Identifying biochemical characteristics that contribute to improved tolerance to high temperature might be useful in cultivar screening programs to maintain year-to-year yield stability. Technical Abstract: Because a number of reproductive processes must occur in highly concerted fashion during the progamic phase (from pollination to fertilization) for successful fertilization and seed production to occur, final yield in cotton is exceptionally sensitive to high temperatures during the flowering period. High temperatures typical of those experienced during a normal growing season in the U.S. Cotton Belt are sufficient to significantly inhibit fertilization, seed set, and yield in thermosensitive cotton cultivars. Depending upon the duration, timing and severity of the stress, fertilization could be limited by poor gametophyte development, decreased pollen germination, and limited pollen tube growth. Under field conditions, diurnal pollen tube growth rate is extremely sensitive to moderately high temperatures, where exposure to moderately high ambient temperatures (34.6°C) results in slower pollen tube growth rates despite no change in pollen germination or ovule fertilization. Heat stress limits fertilization by decreasing subtending leaf photosynthesis, depleting pistil ATP and carbohydrates, increasing oxidative stress in the pistil, and altering pistil calcium concentrations. Having higher pistil concentrations of ATP and calcium is related to genotypic fertilization thermostability. Furthermore, reproductive thermotolerance in cotton is also associated with having elevated pre-stress antioxidant enzyme activity in both the subtending leaf and the pistil, which is likely an innate mechanism for coping with rapid temperature changes that are common under field conditions. |
