Studies On Effects Of Air Temperature On Heterosis Expression And Yield Seed Production Of Hybrid Cotton

There is a significant heterosis in cotton, and planting hybrid cotton can produce higher yield and better fiber quality. However, hybrid cotton seeds are produced mostly by hand-emasculation and pollination, resulting in a high cost and low efficiency of production, which embarrasses the heterosis use of hybrid cotton. Cytoplasmic male sterile (CMS) plants can't produce functional male gametophytes but can produce functional female gametophytes. If insects, such as bees, are employed to pollinate cotton pollens from restorer to the sterile plants in the field of hybrid seed production, it is more effective and economic. However, this system had not been widely used because of weak restorability in its restorer to cytoplasmic male sterility, especially in high aire temperture. 'Zheda strong restorer', a transgenic strong restorer, was developed and overcame the defect of weak restorability to cytoplasmic male sterility in recipient restorer. If that is true, 'Zheda strong restorer' would have a high value in hybrid cotton production.In order to value 'Zheda strong restorer', the fertility differences between hybrids (F₁) restored by 'Zheda strong restorer' and hybrids (Fl) restored by 'DES-HAF277' were compared by determination of the percentage of viable pollens and the rate of self-fertilized bolls and aborted seed in the different air temperatures during different growth periods. Then the critical temperatures (both the upper limit and lower limit critical temperatures) of these two kinds of hybrids (Fl) when their fertility turns into sterility were searched by keeping them in a given constant temperature. Field experiments were done to study the diversity of yield, quality and agronomic characters between the two kinds of hybrids (F₁) by comparing with their maintainers used as checks, in order to know the hetersosis expression of hybrid (F₁) restored by 'Zheda strong restorer'. We also researched how to improve the hybrid seed production through selection of planting ratios of sterile to restorer plants and pollinating mediums during the blooming period.According to the percentage of viable pollens and the setting rate of self-fertilized bolls and the rate of aborted seeds, the hybrids (Fl) restored by 'Zheda strong restorer' showed a stronger and more stable fertility, their upper and lower limit critical temperatures for turninginto sterility was 37 °C and 13°C, comparing with 35.5 °C and 14°C for the hybrids (Fl) restored by 'DES-HAF277', and 37 °C and 10°C for their maintainer. The yield of hybrids (Fl) restored by 'DES-HAF277' was much lower than the hybrids (Fl) restored by 'Zheda strong restorer', as a result of the high air temperature effect in Hangzhou. Further more, The fibre quality is much better in those hybrids (Fl) restored by 'Zheda strong restorer'. In another word, hybrids (Fl) restored by 'Zheda strong restorer' not only have a significant heterosis but also have stabilization of fertility, all of these make 'Zheda strong restorer' meaningful to promote the heterosis use of hybrid cotton, so we would require a great lot of hybrid seeds. Experiment of hybrid seed production showed that a suitable planting pattern for sterile and restorer plants was important for high hybrid seed yield, for examples, row planting pattern or mixed sowing pattern in a ratio of 2:1 was more suitable than others. We also found that there was a relationship between sugar content in sterile flower tissue and hybrid seed yield, i.e., the more sugar content, the more insects visiting, and the more hybrid seeds. Therefore, it was necessary to select the cotton types which contain more sugar in parent flowers, and it was effective to produce cotton hybrid seeds without hand-emasculation and pollination by using cotton CMS system.