Effect of trans-Bacillus thuringiensis gene on gibberellic acid and zeatin contents and boll development in cotton

Two experiments were conducted to investigate the effect of the Bacillus thuringiensis (Bt) transgene on gibberellic acid and zeatin contents and boll development in cotton using two types of Bt-transformed cultivars. In the 2003 study, boll size and weight, gibberellic acid 3 (GA₃) and zeatin (ZR) contents were investigated from 3 to 45 days after flowering (DAF). In 2004, the flowers were sprayed with GA₃, 6-benzyl adenine (6-BA) or a combination of both, and responses in boll size and weight, and endogenous GA₃ and ZR contents were determined. In comparison to the common parent, Simian 4, overall boll size and weight were lower for the conventional Bt cultivar, Sikang 1, but higher for the hybrid Bt cultivar, Sikang 3. Similarly, the boll GA₃ and ZR contents of Sikang 1 were lower than those of Simian 4, while those of Sikang 3 were higher than Simian 4. The largest difference between Sikang 1 and Simian 4 for boll GA₃ and ZR contents were 18.5 and 25.5%, respectively, observed at 17 DAF. The largest difference between Sikang 3 and Simian 4 for boll GA₃ and ZR contents were 25.5 and 85.7% at 31 DAF respectively. Application of GA₃, 6-BA or a combination significantly increased boll size and weight for the conventional Bt cultivar and Simian 4, but did not have a significant effect on these characteristics of the hybrid cultivar Sikang 3. GA₃ and ZR contents of the conventional Bt cultivar Sikang 1 were also significantly increased by application of these treatments. The combined application of GA₃ and 6-BA tended to have a larger effect than the application of either of them separately, but the differences were statistically not significant. These results suggested that the lower boll GA₃ and ZR contents, which could reduce boll nitrogen metabolism intensity, were responsible for the reduced boll development of the conventional Bt cultivar Sikang 1.