Survival of conidia of Clonostachys rosea on stored barley seeds and their biocontrol efficacy against seed-borne Bipolaris sorokiniana

Survival and biocontrol activity of Clonostachys rosea (isolate IK726) conidia during storage on barley seeds were investigated. The initial density of colony forming conidia on seed was 4x10(3) to 9x10(4) colony forming units (cfu)/seed. After 5 months storage at 4degreesC, the density decreased by less than one order of magnitude and the biocontrol efficacy against seedling blight caused by seed-borne Bipolaris sorokiniana was maintained at a significantly high level (>80% disease reduction) for > 5 months. Conidial survival on seeds stored at 20degreesC declined more rapidly than at 4degreesC, and biocontrol efficacy was significantly reduced after 3-5 months. However, conidia produced on solid media over 20 days survived better than conidia produced in liquid culture and conidia from solid media produced over 12 days. In contrast, when seeds treated with conidia were packed with silica gel and stored at 20degreesC, the cfu density decreased by less than one order of magnitude after 5 months and the biocontrol efficacy was still high after 6 months. A dose-response curve revealed that 10(3) cfu/seed were needed for 80% control of seedling blight. Similar control was obtained in storage experiments when approximately 10(3) cfu/seed were recovered from seed, indicating that conidia which survived also retained a high ability to control disease.