EFFECT OF CONIOTHYRIUM-MINITANS ON SCLEROTIAL SURVIVAL AND APOTHECIALPRODUCTION OF SCLEROTINIA-SCLEROTIORUM IN FIELD-GROWN OILSEED RAPE

In two field trials with oilseed rape, Coniothyrium minitans was appli ed to soil as a maizemeal-perlite preparation in order to determine it s effect on sclerotial survival and apothecial production of Sclerotin ia sclerotiorum. The mycoparasite infected sclerotia and decreased scl erotial survival, carpogenic germination and production of apothecia. Effects were greatest when inoculum of C. minitans was applied in autu mn, at the time of sowing, rather than when it was applied in spring. C. minitans survived in soil for 2 years and spread to adjacent contro l plots and infected sclerotia within those plots. However, despite th e fact that the inoculum potential of S. sclerotiorum was reduced by C . minitans treatment, no disease control was obtained either in trial 1, where disease levels were low (0-20% of plant stems affected), or i n trial 2, where disease levels were high (up to 70% of plant stems af fected). Possible reasons for this failure of C. minitans to control s clerotinia disease in oilseed rape, and strategies to improve its effi cacy in the field, are discussed.