Using resource- and phytohormone-stress phenotypes to identify ash biomarkers of resistance to emerald ash borer (Agrilus planipennis)

Emerald ash borer (EAB) is an alien, invasive, wood-boring beetle that is devastating North American ash (Fraxinus spp.) populations in urban and natural forest settings.  The only viable, long term, large scale management strategy is deployment of host resistance, which has not yet been characterized in ash.  One challenge to characterization has been few observable resistance phenotypes.  It is well known that defense physiology is significantly affected by resource availability or hormonal treatment.  In principle, such treatments can therefore be used to diversify resistance phenotypes and identify mechanisms.  Hence, two ash cultivars previously identified as resistant and susceptible to EAB were subjected to different levels of water-, nutrient-, and phytohormone-stress and diverse resistance phenotypes were generated. Ash growth physiology and phloem metabolic and transcriptomic traits will be correlated with EAB-larval growth and development. Traits identified in this study may be used as biomarkers for selective breeding of North American ash resistant to EAB.