Antagonism and biocontrol potential of Ulocladium atrum on Sclerotinia sclerotiorum

Antagonism and biocontrol potential of Ulocladium atrum against Sclerotinia sclerotiorum were investigated and compared to another biocontrol agent Coniothyrium minitans of S. sclerotiorum. Dual cultural assay on potato dextrose agar revealed that U. atrum was antagonistic to S. sclerotiorum. It could grow over the colony of S. sclerotiorum, but could not parasitize sclerotia of this pathogen. Results of spore germination tests on PDA and water agar (WA) showed that conidia of U. atrum or pycnidiospores of C. minitans had no inhibitory effects on the germination of ascospores of S. sclerotiorum. Conidia of U. atrum germinated more rapidly and germ tubes of U. atrum developed more extensively than ascospores of S. sclerotiorum and pycnidiospores of C. minitans. When petals of canola (cv Westar) were inoculated with spores of U. atrum or C. minitans at 5.4×104 spores/petal (at 24 h before, simultaneously, or 24 h after) and ascospores of S. sclerotiorum at 5.0×103 ascospores/petal and placed on detached leaves of canola, incidence of petal-mediated infection of leaves by S. sclerotiorum was significantly reduced. Moreover, the suppression of colonization of petals by S. sclerotiorum was related to the spore concentrations of these two biocontrol agents. Another test on alfalfa showed that application of U. atrum or C. minitans on senescent petals which remained attached to pods of alfalfa significantly reduced the infection of S. sclerotiorum on pods and seeds of alfalfa. This study suggests that the antagonist U. atrum is an effective biocontrol agent of S. sclerotiorum and the efficacy is similar to that of the mycoparasitic fungus C. minitans.