EVALUATION OF A FUNGAL ANTAGONIST, PHAEOTHECA-DIMORPHOSPORA, FOR BIOLOGICAL-CONTROL OF TREE DISEASES

Phaeotheca dimorphospora, which was first isolated from elm wood and f ound to be antagonistic in vitro against the Dutch elm disease pathoge n Ophiostoma ulmi, was tested for antifungal activity in vitro against other tree pathogens by a variation of the agar layer technique. Phae otheca dimorphospora produced antifungal compounds that were strongly inhibitory against a wide range of tree pathogens in addition to O. ul mi, such as Gremmeniella spp., Armillaria spp., Septoria musiva, Verti cillium albo-atrum, Cylindrocladium floridanum, Phytophthora sp., Nect ria galligena, and Heterobasidion annosum. Under light and interferenc e microscopy, four types of morphological changes were observed in the pathogens tested: swelling of hyphae, production of resting spores su ch as chlamydospores and of sclerotia, extrusion of cytoplasm from hyp hal tips, and bursting and destruction of mycelium. Chloroform-soluble antagonistic compounds were extracted that showed both fungicidal and fungistatic effects on the test organisms.