BIOLOGICAL-CONTROL OF SCLEROTINIA-SCLEROTIORUM BY FILM-COATING CONIOTHYRIUM MINITANS ON TO SUNFLOWER SEED AND SCLEROTIA

Conidia of the biological control agent, Coniothyrium minitans, were a pplied to uninfected and S. sclerotiorum-infected sunflower seeds and to sclerotia of two isolates of S. sclerotiorum by polymer film-coatin g, using a fluidised-bed seed treater. Rates of 5 x 10(6) and 7-14 x 1 0(6) conidia per g of seed and sclerotia were obtained, respectively. The activity of C. minitans was compared to treatments with the fungic ides thiram + fenpropimorph and iprodione. In agar plate tests, C. min itans increased seed germination and decreased recovery of S. scleroti orum from S. sclerotiorum-infected seeds. However, in seedling tests c arried out in a potting compost-soil mix with S. sclerotiorum-infected seeds, C. minitans failed to increase survival of seedlings. A high a nd low rate of thiram + fenpropimorph and a high rate of iprodione fil m-coated onto S. sclerotiorum-infected seeds gave consistently better results than C. minitans in these tests. The film-coating process slig htly decreased the germination of C. minitans conidia recovered from s unflower seeds and sclerotia of S. sclerotiorum, but after storage for 1 year at 10 degrees C C. minitans grew from more than 97% of seed an d sclerotia, and the number of colony forming-units per g seed or scle rotia had declined by less than 1 log(10) unit. In agar plate tests, a ll fungicide treatments were more effective than C. minitans in delayi ng myceligenic germination of film-coated sclerotia, although for scle rotia of isolate JN1, all film-coatings were effective in decreasing t he weight of sclerotia subsequently produced. With isolate SB, only th e C. minitans treatment reduced subsequent sclerotial production. In g lasshouse and field pot bioassays with sclerotia buried in soil for 20 and 34 weeks, respectively, C. minitans completely suppressed apothec ial production and no sclerotia were recovered from the C. minitans tr eatment pots. C. minitans spread to infect sclerotia in other treatmen t pots. In these bioassays, both fungicides were less effective than C . minitans, even though apothecial production was almost completely in hibited and less than 10% of sclerotia were recovered.