In vitro antagonism of Trichoderma and naturally occurring fungi from elms against Ophiostoma novo‐ulmi

Summary The antagonist ability of four fungal endophytes isolated from elms ( T richoderma atroviride GF 13, D iaporthe eres GF 2, D iplodia ulmi GF 5 and Alternaria alternata GF 6) and two fungi from a collection ( T richoderma harzianum and T richoderma virens ) was evaluated against six strains of O phiostoma novo‐ulmi (1, 10, 19, 32, 43 and O ‐ V a), the causal agent of Dutch elm disease. Dual culture tests were established in PDA and MA culture media to test the interactions between pathogenic fungi and potential antagonist ones. The fungi showed varying levels of antagonist capacity against O . novo‐ulmi . Among them, T . atroviride and T . harzianum had the greatest inhibiting effect (around 50%). Culture filtrates and previously inoculated cellophane discs from T . harzianum and T . atroviride also caused growth inhibition of O . novo‐ulmi , with less intensity in strains 10 and 19. The control mechanisms involved in the process were competition, mycoparasitism and the production of soluble and diffusible antifungal metabolites. The new isolate T . atroviride GF 13 was efficient as antagonist. It showed antagonist ability against non‐elm‐derived fungi such as V erticillium, F usarium, A spergillus, R hizopus and P enicillium . These results suggest interesting application possibilities in the biological control of Dutch elm disease.