THE VALIDITY OF IN-VITRO SCREENING METHODS IN THE SEARCH FOR FUNGAL ANTAGONISTS OF SCLEROTINIA-SCLEROTIORUM CAUSING WILT OF SUNFLOWER

A multi-test screening system identified 63 fungal isolates with high in vitro biocontrol activity against Sclerotinia sclerotiorum. A bioas say method was developed using sunflower seedings growing in an unster ilized loam mixture. Twenty-six isolates were tested in a series of fi ve bioassay tests and a significant correlation (P < 0.01) was found b etween sclerotial infection in vitro and the number of healthy plants in vivo. Conversely activity in an in vitro mycelial overgrowth test w as not significantly correlated with activity in vivo. However some is olates showing only mycelial activity still exerted significant diseas e control in both the bioassays at Littlehampton and in three addition al bioassays at Sittingbourne. Only one isolate not previously reporte d showed significant activity in both sets of bioassays and the lack o f consistency in disease control activity by all other isolates, and b iocontrol agents in general, was deemed a major barrier to their use.