Endophyte inoculation enhancesUlmus minorresistance to Dutch elm disease

Abstract

Certain fungal endophytes are known to improve plant resistance to biotic stresses in forest trees. In this study, three stem fungal endophytes belonging to classes Cystobasidiomycetes, Eurotiomycetes and Dothideomycetes were selected among 210 isolates for their potential as enhancers of Ulmus minor resistance to Ophiostoma novo-ulmi. We evaluated phenotypic traits of these endophytes that could be beneficial for O. novo-ulmi inhibition in the host plant. Under in vitro conditions, the Dothideomycetous isolate YCB36 strongly inhibited O. novo-ulmi growth, released antipathogen VOCs, chitinases and siderophores, and overlapped with the pathogen in nutrient utilization patterns. These functional traits could explain the 40% reduction in leaf wilting due to O. novo-ulmi in elm trees pre-inoculated with this endophyte. Ulmus minor trees responded to endophyte inoculation with increased stomatal conductance and higher amounts of flavonoids and total phenolic compounds in xylem tissues, suggesting induction of defence metabolism.