Analysis of three biological control agents and naturally-occurring fungal colonizers on the survival of sclerotia of Botrytis squamosa, Sclerotinia sclerotiorum and Sclerotium cepivorum

Management of sclerotia-forming phytopathogenic fungi is difficult due to the resilience of their sclerotia within soil. This thesis assessed the efficacy of three biological control agents (BCAs), Coniothyrium minitans, Microsphaeropsis ochracea, and Trichoderma atroviride, on laboratory-produced (LP) sclerotia of Botrytis squamosa, Sclerotinia sclerotiorum and Sclerotium cepivorum under field conditions for 20 months. Trichoderma atroviride was most consistent, reducing survival of B. squamosa and S. sclerotiorum to 19 and 23%. S. cepivorum did not vary. Further investigations compared the survivability of LP and field-produced (FP) sclerotia of S. sclerotiorum. Survival of LP sclerotia of S. sclerotiorum was greater than that of FP, which were heavily colonized with other fungi. Colonizers were isolated, identified, and evaluated for antagonistic and pathogenic abilities. 80% of isolates demonstrated antagonistism, and two isolates demonstrated pathogenicity. It is evident that sclerotia are not sterile propagules, and that antagonistic soil-dwelling microorganisms are important influential factors on sclerotial survival.