Effects of Temperature and Light on Photosynthetic Heterosis of an Upland Cotton Hybrid Cultivar

The hybrid vigor of crops is related to photosynthesis. However, the effects of environmental factors on the heterosis of the net photosynthesis rate (Pn) of upland cotton (Gossypium hirsutum L.) hybrids remain largely unknown. The objective of this study was to identify the relationship between the heterosis of Pn and temperature and light intensity by using reciprocal hybrids of upland cotton (G. hirsutum cv. Xiangzamian 3) and their corresponding parental lines at the flowering-boll stage. Both the effects of heterosis on the diurnal variations of Pn throughout the day and Pn responses to light under different temperatures in the fourth leaves from the tops of the main stems were surveyed. The maximum values of Pn for all plants were observed at 1000 h. A reduction in Pn was noticeable between 1000 and 1200 h. The maximum heterosis of the obverse F(1) and reverse F(1) of Pn was observed between 1300 and 1700 h under high light intensities (>1000 mu mol m(-2) s(-1)), high temperatures (>= 40 degrees C), and low relative humidity (<= 40%). The effects of heterosis on the self-cooling abilities of the F(1) leaves may be related to the heterosis of Pn in the hybrids that were under heat stress. The resistance of hybrids to high temperatures under high light intensities may act as the heterotic mechanism affecting cotton photosynthetic rates and may also allow for a new method of selecting cotton cultivars with high Pn.