Moving beyond resistance management toward an expanded role for seed mixtures in agriculture

• Seed mixtures (refuge-in-the-bag) are now used for resistance management in Bt corn.
• Crop productivity and pest management can be improved via cultivar mixtures.
• Acceptance of Bt mixtures affords an opportunity to build more diversity into crops.

Insect resistance management for Bt traits in corn has recently moved toward refuge-in-the-bag, which consists of simple cultivar mixtures of susceptible and resistant hybrids. The purpose of these seed mixtures has thus far been solely to maintain susceptible pest insects, which will help prevent the development of resistance and preserve utility of the technology. It appears that this narrow focus on resistance management overlooks broader production benefits that may be achieved by planting genotypically diverse cultivar mixtures. While not yet widely employed in modern agriculture, cultivar mixtures have been successfully used for disease management, demonstrating that the strategy is logistically feasible for intensified agriculture. Evidence from both natural and agricultural systems demonstrates that more genotypically diverse plantings can increase yield or productivity through a variety of mechanisms. These effects are in part attributable to improved response to both abiotic and biotic stressors, such as drought, temperature stress, competitors, herbivores, and disease. Similar to transgenic traits, cultivar mixtures also hold promise for resistance management for traditionally bred, or native, traits.