Influence of different drying temperatures for solid substrate after fermentation on conidia characteristics of the entomopathogenic fungus Beauveria bassiana

Abstract:

[Objective] This study was to evaluate the effect of drying temperature for solid substrate after fermentation on conidia characteristics of entomopathogenic fungus Beauveria bassiana. [Methods] Seven constant or varied temperatures between 28oC and 35oC were designed for drying the solid substrate and the quality of harvested conidia was analyzed. [Results] The results showed that the drying treatments at varied temperatures significantly decreased bacterial contamination in the harvested conidia powder. The conidia viability and germination speed were varied with different drying treatments. After drying at 35℃ for 5 h, there was no significant difference in viability between the dried and fresh conidia, while the median germination time (9.6 h) of the dried conidia was shortened by 9.3%. The tolerance of conidia to heat and UV radiation was increased by drying treatment. Compared to the drying treatment at a constant temperature at 28℃ or 35℃, some varied temperature treatments were in favor of enhancing the stress tolerance of conidia. Drying treatments influenced accumulation of trehalose in harvested conidia, while neither heat resistance nor UV tolerance of conidia was obvious correlation with trehalose level. Optimizing drying temperature could increase the virulence of B. bassiana. After drying at 28℃ for 24 h and then 35℃ for 2 h or at 35℃ for 5 h, the LT50s to Myzus persicae at the dose of 370-450 conidia /mm2 were shortened by 10.6 h and 7.5 h, respectively. [Conclusion] The results suggested that the drying temperature for post-fermentation solid substrate has an important influence on bacterial contamination in the harvested conidia powder, spore viability, stress tolerance and virulence in B. bassiana.