Survival of Coniothyrium minitans associated with sclerotia of Sclerotinia sclerotiorum in soil

The development and survival of the mycoparasite Coniothyrium minitans associated with sclerotia of the plant pathogen Sclerotinia sclerotiorum was studied in pasteurised and non-sterile (untreated) soil. Using scanning electron microscopy, developing pycnidia were first seen within the sclerotial medulla at 7 days post-inoculation with the mycoparasite in pasteurised soil. However, by 14 days post-inoculation, pycnidia had developed fully in both pasteurised and non-pasteurised treatments, and conidial droplets were exuded onto the outer surface of the infected sclerotia. Thirty days post-inoculation, irrespective of soil treatment, the majority of the sclerotial medulla had been converted to pycnidia, with the sclerotial rind remaining largely intact. The pycnidia and dried intact droplets were still observed 6 months post-inoculation with C. minitans, although the conidia on the outer surface of the dried droplets had largely collapsed by this stage. Germinability studies at 10 months post-inoculation showed that approximately 13% of the conidia in dried droplets were still viable. This work shows the potential for infected sclerotia of S. sclerotiorum to provide a unique reservoir for the survival of C. minitans.