VIABILITY,VIRULENCE AND STORAGE OF VACUUM-DRIED BEAUVERIA BASSIANA CONIDIA POWDER / 微生物学通报

ABSTRACT

The fresh conidia powder of Beauveria bassiana SGBB8702 produced with diphasic technology was dried using 36-h procedures of vacuum-freeze drying (VFD) or vacuum drying (VD). The VFD and VD procedures reduced water content of the fresh conidia powder from 58.56% to 3.97% and 4.26%, resulting in preparations containing 1.29, and 1.25?10 11 conidia/g. The VFD or VD conidia had the same viability (≥98%) as the fresh ones but germinated slightly more slowly than the fresh ones. The estimates of LC 50 s for the fresh, VFD, and VD conidia against Myzus persicae on day 7 after inoculation were 1.15, 5.89, and 2.95?10 4 conidia/ml, respectively. At the concentration of 10 6 conidia/ml, the LT 50 of the fresh conidia against M. persicae was estimated as 3.6 d, corresponding to 3.9 d and 4.4 d for the VFD and VD conidia, respectively. Due to much lower cost, the VD procedure was of greater potential for drying B. bassiana conidia in mass production though the VFD procedures resulted in slightly better quality of conidia powder. The viability and virulence of the VFD conidia were assessed periodically during 12-mon storage at 4℃ and 20℃, respectively. No viable conidia stored at 20℃ were detected 255 d after storage whereas those stored at 4℃ had a viability of 90.15% and an LT 50 of 4.7 d at the end of 12-mon storage. The results showed that storage of B. bassiana conidia powder at ambient temperature was unable to maintain shelf life at commercially acceptable level even though its water content was reduced to