Submitted to: Journal of Cotton Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 6, 2003
Publication Date: March 3, 2004
Citation: Adamczyk Jr, J.J., Meredith Jr, W.R. 2004. Genetic basis for variability of cry1ac expression among commercial transgenic bacillus thuringiensis (Bt) cotton cultivars in the United States. Cotton Science. 8:17-23. Interpretive Summary: Cotton varieties genetically engineered to contain Bacillus thuringiensis(Bt)provide excellent control of the target pests (i.e. pink bollworm and tobacco budworm, two key caterpillar pests of cotton), but only moderate control of other caterpillar pests. However, previous work has shown that not all cotton varieties contain the same levels of Bt. We designed a set of breeding experiments to determine if these differences in the level of Bt were under simple genetic control. Our data showed that genetic background has a major effect on Bt expression among varieties, and that only a small number of genes are involved. Thus, these data provide key information to breeders by designing methods to improve the efficacy of Bt cotton against all caterpillar pests.
Technical Abstract: The amount of Cry1Ac in transgenic Bacillus thuringiensis Berliner (Bt) or Bollgard® cotton varies among commercial cultivars. The objective of this study was to determine if differences in overall expression among commercial cultivars of Bollgard® cotton were under simple genetic control. If so, these findings could influence the way breeders select cultivars by selecting for efficacy in addition to agronomic traits. Two sets of crosses were made in the greenhouse with a high expressing and a low expressing cultivar. The subsequent generation was planted in the field. The amount of Cry1Ac was quantified using a commercial ELISA. Highly significant variances within two F2 breeding populations were due to genetic segregation for Cry1Ac expression. Using the modified Castle-Wright formula, estimation for the number of contributing genes for both breeding populations was small. These data show that genetic background has a major effect on Cry1Ac expression. Because backcrossing is the primary method used by commercial cotton breeders, the selection and use of donor and/or recurrent parents that will result in a high level of Cry1Ac expression should be a vital component of transgenic breeding.