UV protection and shelf life of the biological control agent Clonostachys rosea against Fusarium graminearum

Abstract

Fusarium graminearum is the main causal agent of Fusarium head blight (FHB) and produces the health-threatening mycotoxins deoxynivalenol (DON) and zearalenone (ZEN). The fungus Clonostachys rosea has potential as a biological control agent (BCA) against FHB. In this study, we first evaluated the shelf life of mass produced C. rosea as well as the tolerance of different strains to ultraviolet (UV) radiation. At 5 °C storage temperature, C. rosea maintained unchanged viability for two years, while at room temperature, the survival decreased significantly after four months. Exposure of conidia to increasing duration of UV radiation revealed a strong negative correlation with their germination rate and no difference between strains. Subsequently, we screened formulations to protect conidia from harmful radiation. An emulsion with sunflower oil and the sunscreen Escalol 557 (2-ethylhexyl-4-methoxycinnamate) showed excellent protection of the conidia with germination rates between 80 and 96% after UV exposure compared with 7% in water. In climate chamber and field experiments, we quantified the effects of C. rosea with and without UV protection against the infection of wheat by F. graminearum. In the climate chamber, application of the C. rosea strains 016, SHA77.3 and NBB2.9 without UV protection reduced the average contamination with DON by 42 to 82%, whereas the combinations with the formulation significantly increased the ZEN content in grains. In the field, strains 016 and SHA77.3 together with UV protection reduced DON by 45 to 69%, but showed no effect on ZEN. The findings of this study underline the crucial importance of formulations for C. rosea, enabling this BCA to substantially reduce FHB and the accumulation of mycotoxins.