ASSESSMENT OF PHAEOTHECA-DIMORPHOSPORA FOR BIOLOGICAL-CONTROL OF THE DUTCH ELM DISEASE PATHOGENS, OPHIOSTOMA-ULMI AND OPHIOSTOMA-NOVO-ULMI

The antagonistic fungus Phaeotheca dimorphospora was tested as a bioco ntrol agent against the Dutch elm disease pathogens, Ophiostoma ulmi a nd O. novo-ulmi, on Ulmus americana seedlings in the glasshouse. Curat ive inoculation of seedlings with P. dimorphospora had no significant effect on disease development. Conditioning inoculation of seedlings w ith the antagonist protected them against O. ulmi but not against the more aggressive O. novo-ulmi. In seedlings challenged with both the an tagonist and either one of the pathogens, P. dimorphospora only spread locally around the inoculation point; however, the pathogens spread s ystemically throughout the whole plant. O. novo-ulmi survived in the r egion colonized by P. dimorphospora, whereas O. ulmi did not.