| In the recent years, breeding and utilization of insect-resistant transgenic cotton has become one of effective approaches to increase yield, improve the resistance to cotton bollworm (Heliothis armigera), and fiber quality. The released insect-resistant cotton hybrids have been playing an important role in cotton production up to now. Recently a high yield and good quality Bt- hybrid cotton, named "Cikangza 3" was developed by Cixi Agricultural Research Institute of Zhejiang province. Accordingly, the relevant experiments were conducted in this research to study the performance of Cikangza 3 in regional test, and its characteristics of development, yield and physiology and as affect by main agronomic factors, in order to provide scientific evidences for its practical application. The main results obtained are as follows:Cikangza 3 has been successively better in adaptability, yield, insect resistance, and fiber quality in regional test and field demonstration since 1999, with better comprehensive traits, compared with the other insect-resistant cotton cultivars in China, and proved to be one of the leading hybrid Bt-cotton varieties. Its lint yield was significantly higher than that of Simian 3 by 9.5% and 8.65% in Zhejiang regional test of year 1999-2000 and by 24.22% in field demonstration of year 2001. Meanwhile, in Yangtse Rive Valley regional test the yield of Cikangza 3 was 6.83%, and 14.15% significantly higher than that of the control CCRI 29 in 1999 and Simian 3 in 2000, respectively, and 19.07% higher over the main varieties cultivated widely in each province in 2001 production test. In addition, fiber specific strength and yarn quality of Cikangza 3 obtained in 1999-2000 regional test in Yangtse Rive Valley were much better than Simian 3 and CCRI 29, while its 2.5% span length being a little shorter than that of CCRI 29 and similar with Simian 3. As to insect-resistance, the rate of injured boll was mitigated by 85.96% compared with the control HG-BR-8 in Yangtse Rive Valley regional test, and high bollworm-resistance was also observed in lab biological measurement. Furthermore, it performed high resistance to pink bollworm (Pectinophora gossypiella), being 82.9% lower in injury rate than CCRI 12. The damage rates injured by the third and fourth bollworm generation was 88.74% and 95.55% lower than that of Simian 3 in Cixi regional test in 1999, and 1.97% and 0.48% flower-injured rates was observed by the first and second pink bollworm generation, respectively, and pink bollworm number in 100 bolls was significantly lower than that of Simian 3.The main results obtained from the study on the heterosis of growth and some physiological traits are as follows: (1) yield and yield components: the heterosis of individual boll retention potential was observed in Cikangza 3, and its individual lint yield was 19.27%, 16.84%, and 5.17% higher than the mean of its parents, Simian 3 (CKl), and CCRI 29 (CK2), respectively. (2) Plant development characters: square number per plant of Cikangza 3 was 14.75%, 34.01%, and 15.04% significantly higher than the mean of its parent and CKl and CK2. Correlation analysis showed that there was a significantly positive relationship between seed cotton yield per plant and its total effective fruiting nodes (r=0.8622**), suggesting that the increase in total effective fruiting nodes is a major cause for fully exerting the individual production potential and the main strategy for high yield cultivation. In addition, the daily increases in boll number per plant of Cikangza 3, during the peak boll setting period, was 18.03%, 16.60%, and 28.57% higher than that of its male- and female parent, and Simian 3, but no significant difference with CK2, indicating that much more bolls was produced during the peak boll setting stage with suitable light and temperature conditions, which is beneficial to increase the boll number during July 15 to September 15 (bolls set after summer), but produce few bolls before July 15 (bolls set before mid-summer) and decrease rot boll, and therefore...
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