|Reddy, K. Raja|
Submitted to: Physiologia Plantarum
Publication Type: Review Article
Publication Acceptance Date: 1/4/2005
Publication Date: 6/1/2005
Citation: Zhao, D., Reddy, K.R., Kakani, V.G., Koti, S. and Gao, W. 2005. Physiological causes of cotton fruit abscission under conditions of high temperature and enhanced UV-B radiation. Physiologia Plantarum. 124:189-199. Interpretive Summary: Global warming and increasing solar ultraviolet-B (UV-B) radiation at the Earth's surface are two major concerning factors in climate change. Although responses of crop physiology, growth, and yield to one factor of temperature or UV-B radiation have been extensively studied, knowledge of their interactive effects on crops, especially cotton, is limited. Increased cotton fruit abscission under stress conditions is a major cause of yield loss. We conducted a study in sunlit growth chambers to determine the interactive effects of high temperature and UV-B radiation on cotton square and boll abscission, leaf photosynthesis, and nonstructural carbohydrate concentrations in leaves, squares and bolls. Six treatments included 30/22 °C (optimum) and 36/28 °C (high) day/night temperatures, and three daily UV-B intensities of 0, 7 and 14 kJ m-2 within each temperature level. Treatments were started from seedling emergence and lasted 79 days after emergence (final harvest). High temperature did not negatively affect leaf photosynthetic rates, but decreased tissue nonstructural carbohydrate contents and boll retention. Square abscission and tissue total nonstructural carbohydrate concentration were more sensitive to enhanced UV-B radiation compared with leaf photosynthesis. High temperature mainly increased young boll abscission, while enhanced UV-B mainly accelerated square abscission. Square and young boll abscission was closely and negatively correlated with nonstructural carbohydrate concentrations in flower buds or bolls. Therefore, photo-assimilate limitation in reproductive organs was a major cause of increasing fruit abscission of cotton plants grown under high temperature and enhanced UV-B radiation conditions.
Technical Abstract: An experiment was conducted in sunlit controlled-environment growth chambers to determine the physiological mechanisms of fruit abscission of cotton (Gossypium hirsutum L. cv NUCOTN 33B) grown in high temperature and enhanced ultraviolet-B (UV-B) radiation. Six treatments included two levels of optimum (30/22 °C) and high (36/28 °C) day/night temperatures and three levels of biologically effective UV-B radiation (0, 7, and 14 kJ m-2 d-1). Both the temperature and UV-B treatments were imposed from seedling emergence through 79 days after emergence (DAE). High temperature did not negatively affect either leaf net photosynthetic rates (Pn) or square abscission, but significantly decreased boll retention. Plants exposed to 7 kJ UV-B radiation retained 56% less bolls than the 0 kJ UV-B control plants at 79 DAE in spite of no significant differences in leaf Pn at squaring and flowering. At 53 DAE, leaf Pn of plants grown in high UV-B radiation (14 kJ m-2 d-1) decreased by 11%, whereas total nonstructural carbohydrate (TNC) concentrations in the leaves, floral buds (squares without bracts), and young bolls decreased by 34, 32, and 20%, respectively, compared with the control plants. The high UV-B radiation significantly increased square abscission. Square abscission was not related to leaf TNC concentration, but closely correlated with TNC in floral buds (r = -0.68***). Young boll abscission was highly correlated with TNC concentrations in both the leaves (r = -0.40**) and bolls (r = -0.80***). Our results indicate that nonstructural carbohydrate limitation in reproductive parts was a major factor associated with fruit abscission of cotton grown under high temperature and enhanced UV-B radiation conditions.