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Title: Obviation of wheat resistance to the Hessian fly through systemic induced susceptibility

Author
item BALUCH, STEPHEN - Monsanto Corporation
item OHM, HERBERT - Purdue University
item SHUKLE, JOHN - Purdue University
item Williams, Christie

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/23/2012
Publication Date: 4/1/2012
Citation: Baluch, S.D., Ohm, H.W., Shukle, J.T., Williams, C.E. 2012. Obviation of wheat resistance to the Hessian fly through systemic induced susceptibility. Journal of Economic Entomology. 105(2):642-650.

Interpretive Summary: 1. A background statement explaining the problem 2. A description of what was found, not what was done 3. A statement stating why the results are important to the producer, consumer, industry, or other user. Hessian fly populations overcome wheat resistance genes within a few years of deployment, leading to the need for continually developing new resistant varieties. An understanding of the interactions of infesting larvae and the host wheat plant will help scientists to better manage use of new resistance genes. We found that a pure infestation of genetically avirulent Hessian fly larvae are not able to survive on resistant plants; however they do survive and develop to adulthood on resistant plants if virulent Hessian fly larvae co-nfest the same plant. This rescue occurs if the virulent larvae infest within 3 days of the avirulent infestation and is not limited to infestations on the same leaf of the plant. This research suggests that virulent Hessian fly larvae directly suppress the defense response of wheat, and the dual infestation provides a refuge for avirulent flies. this is good news for growers because this "refuge" preserves diversity in field populations and keps avirllent insects in the gene pool while decreasing the selection pressure on the insect, which can lead to increased durability of deployed wheat resistance genes.

Technical Abstract: Dual infestation by virulent and avirulent larvae, as is common under field conditions, results in obviation of resistance and ultimately the survival of both virulent and otherwise genetically avirulent larvae. Simultaneous infestations by virulent and avirulent larvae, as well as infestation by virulent larvae hatched up to five days before or three days after avirulent larvae, lead to obviation of resistance. No penalty in growth of avirulent larval was observed during dual infestation, and average time to adult emergence was accelerated compared to growth on plants carrying no R gene. Obviation of resistance was not localized to the leaf being attacked by the virulent larvae, but also functioned in spatial distance on younger leaves. This research suggests that virulent Hessian fly larvae directly suppress the defense response of wheat, thus providing a refuge for avirulent genotypes and preserving diversity in field populations.