[Inheritance and segregation of transformants in cotton with two types of insect-resistant genes]

A plant expression vector containing a chemeric Bt29K gene coding for the active Cry1Ac protein and the arrowhead proteinase inhibition gene API-B was introduced into an elite cotton cultivar Jihe 321 by Agrobactertium tumefaciens. Some insect-resistant cotton lines were developed. Segregation and stabilization of insect-resistant genes in six transformation lines were studied. Based on the results of kanamycin resistant test and insect bioassay using Heliethis armigera, PCR detection and Southern-blot, we found that the inheritance and segregation of Bt gene were complicated, some transformants were in accordance with Mendelian patterns of inheritance in the ratio of insect-resistant plants to non-resistant plants in Ti progeny, yet others were non-Mendelian patterns. But the inheritance and segregation of Bt gene in homozygous transformation lines were one or two pairs of major dominant genes through crossing of insect resistant homozygous lines with non-transformation cotton variety. That the insect resistance phenotype was conditioned by one or two pairs of dominant genes was ascertained in this study. There were two copies of Bt genes in two transformation lines DR248 and DR193, which was reported for the first time. The results were confirmed by Southern-blot. Through observation of segregation population of transgenic plants at different generations, we found that the exogenous Bt gene in cotton genome showed unstable in inheritance in early generations, but the gene could be stabilized through resistance screening generation by generation. The unstability of Bt gene may mean that it need time for the gene to compatibilize cotton genome.