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 antagonism 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 were identified. Antagonism, expressed as a reduction in the rate of tissue colonization by S. sclerotiorum, occurred, whether C. minitans was co-inoculated at the same time, one day before or one day after S. sclerotiorum, 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 after 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 pieces when exposed to C. minitans alone. When the experiments were carried out on non-sterile soil instead of sterile sand, infection of stem pieces by S. sclerotiorum was reduced and recovery of S. sclerotiorum and C. minitans from stem segments was decreased. Seven C. minitans isolates were also screened against Sclerotium cepivorum and Botrytis cinerea and, whereas the effect of C. minitans on S. cepivorum-infected tissue and sclerotia was essentially similar to that observed with S. sclerotiorum, B. cinerea infected tissue and sclerotia were not invaded by the antagonist.