Changed Growth Characteristics with Bacillus thuringiensis Gene Introduction and Nitrogen Regulation in Bt Cotton

Core Ideas Bt cotton cultivars had higher sympodium leaf number and plant height. Bt cotton cultivars had higher growth rates of main stem leaf and lower growth rate of sympodium leaf area. Bt cotton cultivars had higher numbers of fruiting branches, fruiting nodes, bolls, and retained boll rates. N‐deficit and N‐rich treatments affected number and rates of vegetative and reproductive organs. Changes in vegetative and reproductive growth have been widely observed in Bacillus thuringiensis (Bt) transgenic cotton (Gossypium hirsutum L.). The objectives of this study were to determine the characteristics of vegetative and reproductive growth after the Bt gene was introduced into cotton and to study the effect of N on vegetative and reproductive growth to determine if N nourishment could provide a potential mechanism for changed growth characteristics in Bt cotton. Three Bt cultivars (Sikang1, Ccsi41, and Ccsi45), with their current parents (Simian3, Ccsi23, and Jimian7, respectively), were chosen to compare the characteristics of vegetative and reproductive growth and N distribution, in 2011 to 2012; the same six cultivars with two N fertilizer application rate treatments (0 and 450 kg/ha) were further designed to investigate the N regulation impact on growth in 2013. The results indicated that the Bt cotton cultivars had higher growth rates of main stem leaf area, sympodium leaf number, and plant height and a lower growth rate of sympodium leaf area than their parents. Higher numbers and development rates of fruiting nodes, fruiting branches, bolls, and retained boll rates were also observed but lower fruiting branch positions than their parents. The N‐deficit and N‐rich treatments affected both vegetative and reproductive growth of Bt cultivars. The Bt cultivars had reduced numbers and rates of vegetative and reproductive organs under N deficit compared with their parents. These results show that the introduction of the Bt gene changed growth characteristics, including reduced vegetative and reproductive organ development under N deficit.