2012 Annual Report
1a.Objectives (from AD-416):
1) Identify molecular markers associated with resistance to Cry3Bb1 Bt corn in replicated colonies of WCR populations that are reared on isoline or Bt corn.
2) Test the dominance of resistance and fitness costs to Bt corn.
3) Develop colonies with resistance to Cry34Ab1 + Cry35Ab1.
4) Evaluate the potential for cross resistance between current Bt products and stacked events.
1b.Approach (from AD-416):
A genome scan using a large number of SNP markers will be used to identify markers associated with the resistant phenotype. Crosses of resistant and susceptible lines will be developed and evaluated. We will use techniqes of Meils et al. (2008) and Lefko et al. (2008) to develop a set of resistant colonies in both Ames and Columbia. We hope to be able to evaluate for cross resistance between Cry3Bb1 resitance and Cry34Ab1 + Cry35Ab1 resistance. This will depend on successful MTAs, but Syngenta has already agreed that we can evaluate for cross resistance between MIR 604 resistance and resistance to Event 5307.
This work is related to sub-objective 1.A of the parent project: “Develop colonies with resistance to Cry34/35Ab1 and test the effectiveness of different refuge types to delay resistance” and contributes to Component IIa of the National Program 304 Action Plan by developing increased knowledge of the biology, ecology, behavior, genetics of pests, and plant traits conferring pest resistance.
Transgenic corn has been highly effective in rootworm management until recently. In all fourteen attempts, using all four proteins that are targeted for control of corn rootworm, laboratory selection efforts were able to uncover resistance to the targeted proteins in the corn rootworm population in just a few generations. Given this history, it is not surprising that resistance has developed in the field to the product planted over the largest land area and for the most years. It is critical to stay ahead of the curve, if possible. This research aimed at understanding the nature of resistance, cross resistance, and whether or not refuges work in delaying resistance for low-dose rootworm products, will serve as an alert to the U.S. corn industry of potential problems. Our cross resistance work will help growers and industry to understand its transgenic options for management.
Nearly all phases of this project are active at this time. Previously, DNA was extracted from three western corn rootworm populations selected for resistance to Cry3Bb1 transgenic corn as well as from their unselected control lines. These samples were genotyped with the goal to determine if specific molecular markers are associated with resistance to this transgenic product. If so, field populations could be genotyped to determine if the molecular marker associated with resistance is more common now than previously.
Colonies of the western corn rootworm aimed at evaluating “refuges” (planting of non-Bt corn) for delaying resistance to Cry34/35Ab1 transgenic corn are currently in the sixth generation of selection in both Missouri and Iowa. In addition, cross resistance studies between colonies selected to survive mCry3A and eCry3.1Ab have also been conducted in Missouri. Little or no cross resistance was found between resistance to these two products.