Coniothyrium minitans suppress the carpogenic germination and viability of Sclerotinia sclerotiorum sclerotia, alone or in combination with Perlka

The sclerotia of Sclerotinia sclerotiorum show long term persistence in soil and contribute to the difficulty in managing this economically important pathogen. Coniothyrium minitans is a sclerotial parasite and Perlka is a multi-purpose fertilizer known to suppress the sclerotial germination. This study assessed the sclerotial parasitic activity of C. minitans in a box experiment with and without Perlka. Of the 10 isolates of C. minitans initially screened for their sclerotial parasitism, isolate LUPP418 was selected to treat potting compost. Clear plastic boxes (500 mL) were filled with potting compost (30% w/w moisture) and amended with either C. minitans (at 106 spores g‾¹) or Perlka (at field rate of 400 Kg/ha) alone, or in combination. Controls consisted of unamended potting compost. In each box, mesh bags containing five sclerotia were buried into the potting compost and five free, unbagged sclerotia were pressed into the substrate surface. Boxes were incubated at 18°C (14L: 10D light). Carpogenic germination of surface sclerotia were recorded weekly up to 15 weeks. Buried sclerotia were recovered after 15 weeks, surface sterilised and cultured on Potato Dextrose Agar for viability assessment. Coniothyrium minitans and Perlka treatments alone, and in combination, resulted in complete inhibition of sclerotial germination in comparison to the control, with 84.6% carpogenically germinated sclerotia. Coniothyrium minitans alone reduced the sclerotia viability by 97.0%, and in combination with Perlka, by 95.0%, compared to the Perlka only and unamended control (both 100% viable). Coniothyrium minitans with or without Perlka was indicated to reduce S. sclerotiorum inoculum