|Hargarten, Andrea - Former ARS Employee|
|Subramanyam, Subhashree - Purdue University|
|Xiao, Xiangye - Purdue University|
Submitted to: Arthropod-Plant Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2017
Publication Date: 5/20/2017
Citation: Hargarten, A., Nemacheck, J.A., Subramanyam, S., Xiao, X., Schemerhorn, B.J., Williams, C.E. 2017. Physical and metabolic consequences of Hessian fly infestation are more severe on nonhost Brachypodium distachyon than on host-plant resistant wheat. Arthropod-Plant Interactions. doi:10.1007/s11829-017-9542-4.
Interpretive Summary: Genetic tools for analyzing the involvement of defense genes in protecting plants from insects are much more advanced for the model grass Brachypodium distachyon than for wheat. In preparation for future analysis of gene function, we compared the interactions of Hessian fly larvae with its agricultural host, wheat, and with the nonhost B. distachyon. Similarities and differences in the interactions were identified, suggesting that B. distachyon would be an appropriate model for identifying important genes and then testing them in wheat. This work will give us access to verification of defense mechanisms in wheat that would not be available otherwise, and will identify genes and mechanisms to target in breeding for enhancement of wheat resistance against insects.
Technical Abstract: In previous work, the interactions of wheat with Hessian fly have been characterized at both the anatomical and the molecular levels, giving us an understanding of vulnerabilities and strengths in the modes of defense. However, with hundreds of genes responding in both resistant and susceptible wheat, identifying key genes for enhancement during breeding requires precise genetic tools for functional analysis of gene involvement in wheat defense. Due to the large repetitive genome and lack of molecular tools that can accurately assess the function of wheat genes, the many tools available for use with the related model grass Brachypodium distachyon could be used to identify and then test only the most likely genes in wheat. However, success of this strategy requires that wheat and B. distachyon share some commonalities in their interactions with Hessian fly or that mechanisms active in B. distachyon can be transferred to or enhanced in wheat. A comparison of the responses of wheat and B. distachyon to Hessian fly infestation was carried out, focusing on the level of physical changes occurring during resistance. B. distachyon was determined to be a nonhost, using resistance mechanisms with both similarities and differences to the host-plant resistance of wheat. Both plants were able to complete their development with no detectable seed yield penalty imposed by Hessian fly infestation. And both plants exhibited some stunting of leaves that were actively growing while the larvae were attempting to feed. However, wheat caused larvae to die within three to five days after egg hatch, whereas larvae survived, without growing or pupating, throughout B. distachyon development when the plants dessicated during senescence. Consequently, only the lowest three leaves of wheat were stunted in resistant plants, but all leaves on B. distachyon plants exhibited some degree of stunting. In addition, infested resistant wheat underwent precocious initiation and accelerated growth of the upper leaves so that they achieved their maximum length one week earlier than uninfested control wheat plants. Wheat achieved resistance without producing lesions of a hypersensitive response, whereas all B. distachyon plants responded with robust lesions that did not contribute to resistance or negatively impact larval size since the insects were mobile and able to migrate to healthy tissue.