真空干燥球孢白僵菌纯孢粉的活孢率、毒力与贮存期

VIABILITY,VIRULENCE AND STORAGE OF VACUUM-DRIED BEAUVERIA BASSIANA CONIDIA POWDER

采用真空冷冻干燥法 (冻干 )和真空室温干燥法 (抽干 )对球孢白僵菌 (Beauveriabassiana)原菌粉进行了干燥工艺的比较。在固体产孢基质上生产的新鲜纯孢粉 (原菌粉 )含水量达 5 8 65 % ,经 36h冻干或抽干 ,孢子粉的含水量分别降至 3 97%和 4 2 6% ,含孢量分别为 1 2 9× 1 0 1 1 孢子 /g和 1 2 5× 1 0 1 1 孢子 /g ,活孢率分别为 99 0 %和 97 9%。冻干粉和抽干粉之间的活孢率无显著差异 ,但萌发速度不同。原菌粉、抽干粉及冻干粉对桃蚜(Myzuspersicae)在接种后第 7d的LC50 分别为 1 1 5 ,5 89和 2 95× 1 0 4 个孢子 /mL ;在 1 0 6 个孢子 /mL的剂量下对桃蚜的LT50 分别为 3 6d、 4 4d和 3 9d。从生产成本低得多 ,抽干法比冻干法在白僵菌纯孢粉的生产中更有应用前景 ,尽管冻干粉的质量略优于抽干粉。在4℃和 2 0℃下贮存冻干粉并进行为期一年的孢子萌发率和毒力检测。结果显示 ,冻干粉在2 0℃下贮存至 2 5 5d时完全失活而丧失染虫能力 ,而在 4℃下贮存一年后的活孢率仍达90 2 % ,LT50 仅从初始的 3 9d延长至 4 7d。这说明仅通过降低含水量以延长白僵菌孢子粉在常温下的贮存期仍是不可能的。

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 <5%.