EFFICIENCY OF ISOLATES OF CONIOTHYRIUM MINITANS AS MYCOPARASITES OF SCLEROTINIA-SCLEROTIORUM, SCLEROTIUM-CEPIVORUM AND BOTRYTIS-CINEREA ON TOMATO STEM PIECES

Twenty five isolates of Coniothyrium minitans were screened for antago nism to Sclerotinia sclerotiorum in a Petri dish bioassay using tomato stem segments placed on sterile sand. The antagonistic activity of 23 isolates was quite uniform and only two less antagonistic isolates we re identified. Antagonism, expressed as a reduction in the rate of tis sue colonization by S. sclerotiorum, occurred, whether C. minitans was co-inoculated at the same time, one day before or one day after S. sc lerotiorum, but was slightly restricted when S. sclerotiorum was given a lead of one day. On average, 50-80% of sclerotia of S. sclerotiorum formed on the stem pieces were infected by C. minitans two weeks afte r inoculation. Excluding the less antagonistic isolates, Coniothyrium minitans was recovered from over 80% of S. sclerotiorum-infected stem segments when co-inoculated but from a maximum of only 7% of stem piec es when exposed to C. minitans alone. When the experiments were carrie d out on non-sterile soil instead of sterile sand, infection of stem p ieces by S. sclerotiorum was reduced and recovery of S. sclerotiorum a nd C. minitans from stem segments was decreased. Seven C. minitans iso lates were also screened against Sclerotium cepivorum and Botrytis cin erea and, whereas the effect of C. minitans on S. cepivorum-infected t issue and sclerotia was essentially similar to that observed with S. s clerotiorum, B. cinerea infected tissue and sclerotia were not invaded by the antagonist.