Strains of Coniothyrium minitans reduce the emission of apotheciaof Sclerotinia sclerotiorum

Abstract: Sclerotia of Sclerotinia sclerotiorum (Ss) can survive for long time in soil and are themain inoculum source of the white mold disease. An alternative for reducing this inoculum is theuse of parasites, such as Coniothyrium minitans (Cm). We evaluated the potential of Cm isolatesfor the biological control of Ss in beans. The effect of the temperature on the growth of 15isolated of Cm was evaluated in vitro. The hyperparasitism ability of Cm was evaluated in soilinfested with sclerotia and conditioned in pots. The infested soil was treated with conidiasuspension of the antagonists, fluazinan or sterile distilled water. After seven days at 20°C, thesclerotia were removed from soil and placed inside Petri dishes over bean leaves previouslydisinfested. The germination and parasitism of sclerotia were evaluated after 7 to 10 days. Toevaluate the apothecia emission, soil infested with sclerotia of Ss and treated as described wasmaintained at 18°C and the number of emerged apothecia was counted up to 84 days afterinoculation. The emergence of bean plants in soil infested with sclerotia and mycelium of thepathogen and treated as described was evaluated in greenhouse. The ideal temperature for growthof Cm isolates varied from 18 to 19°C and at 30-35°C they were complete inhibited. The isolatesof Cm promoted less than 10% of reduction in viability of the sclerotia, but they significantlyreduced the emission of apothecia. Two isolates increased the emergence of plants in relation tothe inoculated check, but was significantly lower than the non-inoculated check. Field tests willbe conduct to confirm the potential of the selected isolates to reduce the inoculum source of thepathogen.