Exogenous Dopamine and Overexpression Enhance Apple Resistance to .

, one of the main pathogenic fungi involved in apple replant disease (ARD), is a serious threat to apple growth and development. Dopamine and tyrosine decarboxylase (TyDC), a key enzyme in the dopamine synthesis pathway, have been reported to play an active role in plant responses to biotic and abiotic stresses, but little is known about the functions of dopamine and () in the interaction between and apple roots. In this study, seedlings treated with exogenous dopamine and apple plants overexpressing were inoculated with ; both treatments reduced the root system damage caused by . After inoculation with exogenous dopamine increased dopamine content in the seedlings; alleviated the inhibition of biomass accumulation; increased root metabolic activity, photosynthetic efficiency, and antioxidant enzyme activities; reduced reactive oxygen species accumulation; and upregulated the expression of genes encoding chitinase, β-1,3-glucanase, and pathogenesis-related proteins. Similar results were observed in -overexpressing apple plants. In addition, the overexpression of increased tyramine content and the deposition of cell wall-bound amines in roots. Overall, our results reveal that exogenous dopamine and overexpression of enhance apple resistance to , which is an important application for the prevention of ARD.