Physical and metabolic consequences of Hessian fly infestation are more severe on nonhost Brachypodium distachyon than on host-plant resistant wheat

Physical and metabolic changes were compared between the model grass, Brachypodium distachyon , and the Hessian fly host plant, wheat, after infestation. B. distachyon was determined to be a nonhost, where 13 lines were resistant to all infestations tested, yet it responded with characteristics of both host-plant resistant wheat and susceptible wheat. Similar to resistant wheat, B. distachyon completed development with no seed yield penalty imposed by Hessian fly infestation. Wheat and B. distachyon exhibited some degree of leaf stunting, but only of the leaves that were actively growing while the larvae were attempting to feed. Since resistant wheat killed all larvae within 3–5 days after egg hatch, only the lower leaves were stunted. In compensation for leaf stunting, infested resistant wheat underwent precocious initiation and accelerated growth of the upper leaves once the larvae had died. In contrast, larvae survived, without growing, on B. distachyon for much longer, some up to 46 days after egg hatch when the plant was senescing; consequently, all leaves of B. distachyon exhibited stunting, but to a lesser degree than leaves of susceptible wheat where the insects complete their life cycle. Transcript profiling of eight key genes, known to respond to Hessian fly in either resistant or susceptible wheat, demonstrated that B. distachyon exhibited responses intermediate between the compatible and incompatible interactions of wheat as well as both type I and type II nonhost resistance.