TRICHOTHECIUM ROSEUM, A MYCOPARASITE OF SCLEROTINIA-SCLEROTIORUM

Among sclerotia of Sclerotinia sclerotiorum collected from diseased be an plants in a field near Lethbridge in 1987 and 1988, 30 and 16%, res pectively, were contaminated by Trichothecium roseum. Laboratory studi es showed that T. roseum is a mycoparasite of S. sclerotiorum, able to infect and destroy sclerotia in dual cultures on potato dextrose agar . Among sclerotia inoculated with spores of T. roseum and incubated fo r 4 weeks on moist sand, 54 and 43 % were infected and killed by the i solates TR-4 and TR-6, respectively. Transmission electron microscopic studies of infected sclerotia revealed that hyphae of T. roseum enter ed the rind tissue by penetrating the melanized cell walls or via junc tions between cells. Lysis of host cell walls occurred at penetration sites. Hyphae of T. roseum ramified in cortical and medullary tissues, destroying the sclerotium. In sclerotia with light infections of T. r oseum, numerous cortical and (or) medullary cells showed cytoplasmic g ranulation and vacuolization without direct association with the mycop arasitic hyphae.