Study On Photosyntheticbasis Of Heterosis And Screening For High-Temperature Tolerance In Cotton

The character of cotton yield has a obvious heterosis. The basic of yield formation is photosynthesis of leaves, but the character of heterosis with cotton photosynthesis and the relationship with yield was rarely studied. The photosynthesis of leaves has a close relationship with temperature. The growing season of cotton is summer with high temperature. High temperature is bad for photosynthesis of leaves, so influence on yield and quality of cotton. Now, screening indexes of heat tolerance of cotton photosynthesis were not defined. These questions are influence on choosing cotton with high tolerance. The major results are as follows:The Siza3and Zhongmian48cotton cultivars applied in this study were used to test the gas exchange and fluorescence parameters in them and their parents under high temperature. Strong light and various concentration of CO2. The results showed that the net photosynthetic rate and stomatal conductance of Siza3under high temperature and strong light at noon and recovering stage in the afternoon show significant superiority over better parents at the boll opening stage. The higher the concentration of CO2, the higher the net photosynthetic of Siza3. Under the condition of the varied concentration of CO2, the stmatal conductance of Siza3and Zhongmian48dosen’t show significant heterosis, the stomatal conductance dosen’t show obvious relationship with heterosis of the net photosynthetic has a close relationship with the concentration of CO2. When concentration of CO2is lower or higher than atmospheric concentration of CO2(400μmol·m-2·s-1), heterosis of the net photosynthetic shows significant.The superiority over better parents of Siza3under high temperature, strong light and various concentrations of CO2is more significant that of Zhongmian48.under different environment, all the photosynthetic parameters dosen’t show significant heterosis.Under high temperature and strong light, the photorespiration of Siza3is obviously lower than its parents and performs the negative superiority over better parents. Plabs relates with heterosis of the net photosynthetic.Simian3, Sumianl2and Sumian22in different growth and development periods under constant, growing and room temperature conditions were used to test the fluorescence and light response curves of the three cultivars, and aim to screening indexes that is closely related with the net photosynthetic and easily determined. The results show that:the turning points of Fo of the three cultivars in the same period show the following trend:Sumian22> Sumianl2>Simian3, indicating that the stability of oxygen evolving complex is:Sumian22>Sumian12>Simian3. The Fv/Fm, Plabs and NPQ of different cultivars under different growth and development periods show:Sumian22>Sumian12>Simian3; the changes in Vk show:Sumian22>Sumian12>Simian3, indicating that the sensibility of PSII and the efficiencies of photosynthetic electron transport of Sumian22is lower than these of Sumianl2and Simian3.The turning point of Fo of Sumian22is lower than that of Simian3and Sumian12, indicating that the stability of PSII of Sumian22is higher than that of Simian3and Sumian12. With the development of the cultivars under different periods, the turning point of three cultivars increases gradually. The net photosynthetic of Simian3, Sumian12and Sumian22has a high correlation with Vk and PIabs. The Fv/Fm, PIabs, NPQ Fo and Vk of different cultivars show significant difference during budding period. So the Vk and Plabs leaves were determined at constant temperature (28℃-48℃) during budding period, which are the parameters to judge the heat tolerance of photosynthetic of cotton cultivars.