Contamination of non-Bt cotton fields by transgenic Bt cotton

View the project final report

Commodities

• Agronomic: cotton
• Animals: bees

Practices

• Crop Production: application rate management
• Education and Training: extension, on-farm/ranch research
• Farm Business Management: risk management, whole farm planning
• Pest Management: biological control, genetic resistance, integrated pest management, prevention
• Production Systems: agroecosystems

Transgenic Bt cotton produces toxins that control many insect pests, while affecting fewer non-target organisms than most conventional insecticides. However, Bt transgenes can disperse into other cotton varieties, resulting in agricultural problems. For example, such contamination could potentially reduce the efficacy of refuges, which are used to delay insect resistance to Bt crops. Additionally, if contamination occurs in seed production fields, the genetic purity of non-Bt cotton varieties could be undermined. In preliminary work, we discovered two forms of Bt contamination in commercial non-Bt cotton fields: outcrossed cotton seeds and adventitious Bt plants. Outcrossed cotton seeds result from pollen-mediated gene flow from nearby Bt plants, whereas adventitious Bt plants result from the accidental planting of Bt seed in non-Bt fields. Adventitious Bt plants may enter fields through inadvertent seed mixing at the gin or during planting, outcrossing of Bt cotton into non-Bt seed production fields, or volunteers from previous years’ crops. Outcrossed and adventitious Bt plants are integrally linked, as outcrossing in seed production fields could lead to future generations of adventitious Bt plants, and as pollen from adventitious plants can outcross neighboring non-Bt cotton. In this study, we will examine the multiple components of Bt contamination in commercial non-Bt cotton fields, particularly in fields used for seed production. We will examine the factors that influence gene flow into non-Bt fields, which may include pollinator activity, distance between Bt and non-Bt fields, occurrence of adventitious Bt plants in fields, and cultural practices of cotton growers. Our goals are to create a model that predicts the rate of contamination increase in fields based on the aforementioned variables, and to design recommendations to assist growers in protecting their fields from Bt contamination.

• 1) Determine the importance of seed bags as a source of adventitious Bt plants. 2) Identify factors that influence the level of Bt outcrossing in non-Bt cotton seed production fields. Specifically, examine adventitious Bt plants, landscape attributes, and bee activity as potential explanatory variables. Also examine the potential for human error to contribute to the presence of adventitious Bt plants. 3) Identify changes needed in seed production guidelines to reasonably limit contamination.