Undesired Changes in Bt Cotton Boll Characteristics Explained

Chinese researchers explained that the differences observed in boll characteristics among three Bt cotton varieties was due to varying contents of two plant hormones: gibberellic acid 3 (GA₃) and zeatin (ZR). The researchers conducted a study to determine the cause of significant changes in boll characteristics when a Bt gene was introduced into a non-hybrid cotton.

The researchers compared boll characteristics of three Bt cotton varieties - Sikang 1, a conventional cultivar, Sikang 3, a hybrid cultivar, and Simian 4, the common parent of these two cultivars. They observed that compared to their common parent, Sikang 3 had larger bolls while Sikang 1 had lower boll size and weight. 

The lower endogenous ZR and GA₃ contents in bolls of the Sikang 1 variety resulted in a reduction in boll nitrogen metabolism intensity and reduced boll development, says the group of Yuan Chen. Sikang 1 was not developed through backcrossing, but was derived by outright selection of regenerated transformed plants from Simian 4. Chen and colleagues recommend that backcrossing be followed to harness the benefits offered by both transgenic and conventional breeding methods, as what was done in Sikang 3.

 For more details, the paper published in the journal Field Crops Research can be accessed by subscribers at http://dx.doi.org/10.1016/j.fcr..04.003