Abstract:

Planting CMS-based hybrid cotton is an important way to use cotton heterosis. Fertility of hybrid cotton pollens is influenced by cultivar, climatic conditions, management practices and pests. Among all the factors, temperature is the primary one affecting cotton growth, the following is air humidity. Stability of pollen fertility under high and low temperature stresses, associated with the heterosis expression of CMS-based hybrids, is the main point to elucidate in this study. The fertility differences between hybrids and the maintainer were compared by testing the percentage of fertile pollens in the greenhouse experiment with temperature controlled and the field experiment with natural temperature. In addition, percentage of setting bolls and percentage of aborted seeds were tested in the field experiment.Pollen fertility was checked by benzidine-Naphthol fluorescence microscopic method, while cross-pollination experiments were performed by dusting pollen obtained from corresponding restorers, then percentage of setting bolls and percentage of aborted seeds were determined by calculating the number of bolls or seeds, respectively. The critical temperatures for upper limit and lower limit were searched from different given consistent temperatures, which each temperature was kept for eight days in the greenhouse when cotton pollens turned from fertility to sterility. The results showed that the response of CMS-based hybrids to the extreme temperature stress was more sensitive than that of the maintainer, while the former usually had lower stability in pollen vitality under the stress. However, different CMS-based hybrids had various tolerances to temperature stress, for example, hybrids (F₁) restored by Zheda strong restorer showed higher pollen viability, more setting bolls and less aborted seeds under the stress than others. The response of pollen fertility to air temperature had a 5-day’s delay in the field. Furthermore, the changes of maximum air temperature were more consistent with the curve of the percentage of pollen viability than those of average air temperature. It showed that the maximum air temperature for several days before anthesis affected the viability of pollen more salient. The Quadratic model [Y = a (T–T_opt)²+b], applied to analysis the relationship between pollen viability (Y) and temperature (T), was best described as the temperature response functions of pollen fertility. According to actual observation,combined with the predicted value from the model above, the upper and lower critical temperatures for shift of fertility were 38.0℃ and 13.0℃ for hybrids restored by Zheda strong restorer, 36.0℃ and 14.0℃ for hybrids restored by DES-HMF277, and 38.5℃ and 10.0℃ for their maintainer. Compared with the low temperature stress, in the major cotton-growing areas of China, high temperature stress was more widespread, with longer duration and greater impact on yield. Improving the pollen fertility stability of CMS-based hybrid cotton under extreme temperature stress is an important goal in recent breeding program.

Key words: Cotton, Cytoplasmic male sterility(CMS), Temperature stress, Pollen fertility, Critical temperatures