Effects of grafting on host plant resistance in ash (Fraxinus spp.) to emerald ash borer (Agrilus planipennis Fairmaire)

Abstract

Abstract The invasive emerald ash borer (EAB) (Agrilus planipennis Fairmaire Coleoptera: Buprestidae) is a phloem‐boring pest from Asia that has killed hundreds of millions of North American ash trees (Fraxinus spp.). Propagation of trees resistant to EAB must be explored as a tool to maintain the North American ash resource. Interactions between the root and shoot of a tree may be critical to its ability to resist attack by insects and pathogens because many secondary metabolites critical to plant defence are synthesized in the roots. In the present study, we determined the extent to which grafting susceptible green ash (Fraxinus pennsylvanica Marshall) and resistant Manchurian ash (Fraxinus mandshurica Rupr.) affects EAB resistance in ash trees. We measured adult EAB survivorship, herbivory, fecundity and morphological tree characteristics on grafted and nongrafted green and Manchurian ash. Among grafted trees, beetles caged on grafted green ash lived four days longer and laid at least three times more eggs than beetles caged on trees with a Manchurian ash scion or rootstock. Herbivory was unaffected by graft combination. Our findings suggest that grafted trees with Manchurian ash rootstocks or scions will be more resistant to EAB than nongrafted green ash trees.