[Variation in the viability and the metabolism of internally reserved nutrients of Beauveria bassiana conidia during storage at different regimes of water content and temperature].

While the fresh powder (with water content of 58.9 +/- 1.6%) and vacuum-freeze dried (VFD) one (with water content of 7.4 +/- 0.9%) of Beauveria bassiana SGBB8702 conidia were stored at 4 degrees C and 20 degrees C, their viability and contents of internally reserved saccharides and proteins were examined at 5 days intervals. It was found during one-month storage that the water content and temperature interactively affected the levels of conidia viability and the contents of the reserved saccharides and proteins, which in turn correlated considerably well to the viability. Stored at 4 degrees C and 20 degrees C, the VFD conidia lost content of saccharides by 13.4% and 14.1%, content of proteins by 39.2% and 38.2%, and viability by 32.0% and 55.8% when germinating in water only and 6.7% and 10.4% when germinating in 2% glucose solution plus 0.5% peptone, respectively. In contrast, the four estimates of the fresh conidia stored at 4 degrees C and 20 degrees C decreased by 42.4% and 43.2%, 66.3% and 65.4%, 96.4% and 99.4%, and 9.9% and 98.4%, respectively. Thus, water content of B. bassiana conidia affected variation ranges of the viability and the internally reserved nutrients whereas storage temperature influenced their variation rates. However, depletion of the internally reserved nutrients did not necessarily inactivate the conidia. Instead, such conidia may germinate at relatively high level during a period of time as long as being supplied with sufficient nutrients. In another experiment, the powder of VFD conidia with water content being reduced to 4.0 +/- 0.9% were half-monthly examined for viability during one-year storage. The viability only decreased slightly from 99.0% to 90.2% at 4 degrees C by the end of one year. Stored at 20 degrees C, the viability also declined slowly during the first 165 days but dramatically decreased afterwards with little being detected on day 240. A modeling analysis showed that the time for the VFD conidia to lose 50% viability was 1006 days at 4 degrees C and 197 days at 20 degrees C, respectively. Conclusively, the B. bassiana conidia powder, even though its water content was controlled below 5%, can be safely stored for one year or longer at low temperature only but for no longer than 6 months at ambient temperature.