Genetic Effects Of Bt And Its Mapping In Transgenic Cotton

Insecticide application and classical breeding strategy are not efficient approaches to control the damage of insect because of high investment and contamination of environment for chemical compound, and no high resistance gene in upland cotton varieties. The development of plant molecular biology has enabled breeders to transfer insect resistance genes such as Bt and Cowpea trypsin inhibitor gene (CpTI) into cotton. Planting transgenic Bt varieties was approved to be an efficient way to solve these problems. However, the problems of insect resistance to Bt protein, negative relationship between resistance and agronomic traits in the course of planting were found. How to resolve these problems is highly important to make wide use of transgenic cottoaThis research was aimed to investigate Bt's genetic effect and relationship between pest-resistance and agronomic traits with field tests and molecular biology methods. The main results are as follows:1. All the transgenic varieties were highly resistant to boll-worm. The resistant level of different organs were significantly different, the level of pest-resistance were leaves > calyx>bud>flower. 2. In a half diallel cross including 4 parents and 6 hybrids, Bt had significant effect on hybrids' lint yield compared with those without Bt insertion. Among the hybrids with Bt insertion, Bt's expression, pest-resistance level and the combing ability of several iso-gene lines did not change with increasing copies. Bt gene had not gene dosage effect3. Five RFLPs were detected between S3Bt and its original variety S3. Their agronomic traits were also investigated in 1999. Lint percentage and plant height of S3Bt was significantly lower than its original variety S3.4. The pest-resistance levels were negatively correlated with damaged boll percentage in 6 F2 segregant population, but not correlated with other 19 agronomic traits. The significant correlation was also observed between pest-resistance and its mid-parent heterosis of damaged boll percentage in different populatioa Their least correlation coefficient was-0.2830, highest coefficient was -0.7650. Anyway, the correlation coefficient between pest-resistance and bolls number per plant were different in different populatioa No negative Bfs effect on yield component was observed.5. The ratios of Bt segregation in 3 different F2 population were 3:1.2 copies were founded into S3Bt genome, but only one copy had 35S promoter. Locuses of Bt's insertion were different in different varieties.6. The reverse Bt flanking fragments were composed of DNA sequences similar to that of vector, forward Bfs flanking fragments were composed of highly AT repetitive sequence. Becausepercentage of AT was very high in Bt gene, these structures were perhaps important for inserting Bt and maintaining its stability and expression No structure gene was found in the locus of Bt insertion area7. A molecular marker including RFLP, RAPD and SSR linkage map were constructed, the total length was 1275.5cM covering 25.5% of cotton genome. This is first report about constructing cotton genetic linkage map with different molecular markers. Twelve QTLs of lint yield components and fiber length were mapped. Their highest variance contribution was up to 40%.In addition, some strategy to avoid the problem of pest resistant to Bt protein based on the results and constructing linkage map with molecular marker linkage map in cotton were discussed.