| Since 1980s, the cotton breeding in Jiangsu province had achieved significant improvements with respect to the successful selections of a series of super varieties (e.g. Simian 2, Yanmian 48, Simain 3, Sumian 8, Sumian 9, and Sumian 12) in terms of comprehensive attributes, the large scale of more than one million hectare accumulative application area of individual variety, the geographically broad extension scope to several provinces in the Yangtze River valley, and thus contributed prodigious profitability to the society development. However, in recent decade, especially since the cotton hybrids came into use, the new varieties selected in Jiangsu Province could seldom be applied in other provinces, even the cotton seed market in Jiangsu province has partially fallen out to the varieties from other provinces. According to statistics, since the dominant role of Deltapine 15 and other extraneous varieties was gradually replaced by the varieties bred in Jiangsu province (e.g. Simian 2, Xuzhou 142, Yanmian 48 etc.) in the middle of 1980s, the latter had occupied the cotton planting area in Jiangsu province until the seventh launch of cotton variety replacement in large scale in the end of 1990s when the non-transgenic and non-pest-resistant varieties were replaced by transgenic and pest-resistant ones with the consequent decline of planting proportion of 90.9% in 2000 to less than 50% in 2005. Under this critical situation, both cotton breeders and agricultural production managers are paying much more attention to exploring the methodologies of the adjustment of cotton breeding target to promote the cotton breeding level, and thus to ensure needed science and technology for accommodating to the sustainability and stability of cotton production in Jiangsu province in the 21st century. On the basis of above considerations, a historical perspective on the cotton genetic improvement and evolution rules, a summary of the historical successful experiences and the unsettled problems will provide not only valuable guidelines for future cotton breeding, but also important backups for agricultural management department to draw out cotton breeding targets and registration criterion in the future.This paper analyzed the development of cotton genetic improvement by exploitation of cotton multi-environment trials datasets of Jiangsu province in 1979-2006, in terms of the comparisons on lint yield, fiber quality, disease resistant, and agronomic characteristics of the candidate cultivars. And the focus was also put on the comparison on the main properties of hybrids and non-hybrids. It could be concluded as follows:1. The cotton regional trials of Jiangsu Province could be approximately divided into three phases, i.e. the first phase is the coexistence of early and middle matured cultivars with or without the property of disease-resistant; the second one is the coexistence of early and middle matured disease resistant cultivars, and the combination of hybrids and pest-resistant cultivars is the third phase, in which cotton production was developed fastest in Jiangsu province. On the view of the candidates proportion, most parts of the cultivars, accounts for 91.92%, were bred in Jiangsu province.2. Conclusions on cotton genetic improvement of yield and yield-relevant characters were:lint yield, boll number per plant and lint percentage of early matured cotton, middle matured cotton, middle matured and disease-resistant cotton achieved positive progress at different degree; Lint yield of the three types of cultivars increased significantly in the step of 26.63kg/hm2,19.63 kg/hm2, and 20.96 kg/hm2 per year, respectively; Bolls per plant was on the rise at the speed of 0.533 units,0.651 units, and 0.361 unites per plant per year respectively; while lint percentage increased by 0.272%,0.301%, and 0.123% per year respectively. The boll weight of middle matured disease-resistant cotton progressed at 0.034g per year, but the boll weight of early matured cotton and middle matured cotton did not show significant regression relationship with year. Based on the statistical analysis of the whole dataset, we concluded that lint yield, boll number per plant, boll weight, and lint percentage were all significantly increased by 18.61 kg/hm2,0.388 bolls per plant,0.03g per boll, and 0.141% per year, respectively.The contribution of yield components (i.e. boll numbers, boll weight, and lint percentage) to lint yield was obviously discrepant in terms of cotton types. For early matured cotton the contribution ranked as lint percentage>boll numbers>boll weight, early matured disease-resistant cotton was boll numbers>boll weight>lint percentage, middle matured cotton was boll numbers>ling percentage>boll weight, middle matured disease-resistant cotton was boll numbers>boll weight> lint percentage. When we further classified the phase of middle matured disease-resistant cotton into three sub-phases named after the representative cultivars of'86-1'period, Yanmian 48 period, and Simian 3 plus Sumian 9 period, respectively, we found that the contribution of yield components to lint yield were not consistent in different sub-phases. In 86-1 period the weightiness order was boll weight>lint percentage>boll number, in Yanmian 48 period that was boll number> lint percentage>boll weight, while in Simian 3 plus Sumian 9 period that was boll number>boll weight>lint percentage. The discrepancy of contribution order in different cotton types and periods illustrated that the focus of cotton breeding targets in different breeding period for different cotton types was different.3. Compared to the significant genetic gains in yield, the genetic improvement on fiber quality was not so much efficiently in recent decade in Jiangsu province. Due to the restricts of higher micronaire value, there are no suitable varieties for spinning 36 s yarn by rotor spinning and air-jet spinning, so the emphases on cotton fiber quality breeding should be focus on proper micronaire value the harmonization of fiber length, fiber strength and fiber fines, and thus to provide different types of ideal cotton cultivars in content with the potential requirements of spinning industries.4. The genetic improvement gains in disease resistance were effective in terms of the successful cultivar breeding with low indices of Fusarium Oxyzporum during the seventh and eighth five-year program periods. As a result of the breeding emphasis shift to pest resistance since the ninth five-year program and the resultant neglect of resistance selection in Fusarium Oxyzporum, the disease resistant index of Fusarium Oxyzporum was on the rise, leading to a decline of the proportion of resistant and high resistant cultivars. However, we still could see a certain degree of progress in breeding for cultivars resistant to Verticillicm dahliae, with the disease resistant index dropping down at the step of 1.615 per year.5. On the aspect of genetic improvement on main agronomic characters, the plant height, yield percentage before frost, and fruit branches of early matured cotton achieved the significant annual increment of 1.524 mm,1.037%, and 0.289 units, respectively. The fruit branch number and yield percentage before frost of middle matured cotton (including middle matured disease-resistant cotton) increased by 0.07 unit and 0.931%, separately, while the growth period reduced by 0.531d per year.6. The lint yield, boll number per plant and boll weight of hybrids were significantly higher than those of non-hybrid cotton with an average increment of 6.96%,3.35 units per plant and 0.19g per boll, nevertheless, the lint percentage of hybrids was 1.24% lower. The contribution ranks of yield components to yield of hybrids were in context with those of non-hybrids, although the contribution quantitative scales were of somewhat difference. The lint yield improvement of hybrids seemed to be more closely linked with the properties of yield components. According to the partial correlation analysis, we found that the relationships among yield components of hybrids were significantly negative, but for non-hybrids were non-significant negative, which consequently leading to the conclusion that there existed mutual restricting interactions among yield components of hybrids. To further improve hybrids'lint yield at present, it is suggested making an integration promotion of yield components, or introducing new germplasm into breeding program to break through the unfavorable linkages. There was no significant difference in terms of fiber quality and disease resistant index of Fusarium Oxyzporum between hybrids and non-hybrids. The fruit branch number and growth period of hybrids were significantly higher than non-hybrids, and the disease resistant index of Verticillicm dahliae was lower than non-hybrids by 5.25 units on average. |
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