Impact of water content and temperature on the shelf-life of Beauveria bassiana conidia stored in dark
含水量与温度对球孢白僵菌孢子粉贮存寿命的影响及模拟分析

Batches of Beauveria bassiana SG8702 conidia as powder with water content (Cw) of 1.12, 4.73, 7.23, 9.84 and 14.11% were stored in dark at 4 and 25 degrees C during an 18-mon period and monitored at 15-day intervals for viability in order to determine their shelf-lives under controlled conditions. The Cw was found significantly affecting the viability at each temperature. Stored at 4 degrees C, conidial viability always fluctuated above 91% during the first 16 months among the Cw treatments of 1.12%-9.84% with no significant difference from one to another until at the end of 18 months, when the 9.84% Cw treatment had a significantly lower viability than other treatments with lower Cw. The viability in the high Cw treatment (14.11%) was significantly smaller than those in the Cw treatments of 1.12%-9.84% from month 6 onwards and dropped to only 24.2% at the end of 12 months. Stored at 25 degrees C, however, the viabilities differed significantly among the Cw treatments of 1.12%-9.84% on months 3 and 6, respectively, with a remaining viability of only 17.6% in the 9.84% treatment at the end of 6 months. The observed viabilities (Vc) depending on the (Cw) over the time of storage (Ts, months) at each temperature were well fitted to a modified survival model with the coefficients of determination exceeding 0.85. When a viability of 90% was expected on a basis of the fitted model, the shelf-life of B. bassiana conidia stored at 4 degrees C was estimated as 7.3 months at Cw = 12%, 11.2 at Cw = 10%, 14.9 at Cw = 9%, 21.0 at Cw = 8%, 33.0 at Cw = 7%, and 65.5 at Cw = 6%, respectively. Thus, the Cw for long-term storage at 4 degrees C could be controlled at < or = 8%. In contrast, for an expected viability of 80% at 25 degrees C, the shelf-life was estimated as only 1.7 months at Cw = 10%, 2.3 at Cw = 8%, 3.0 at Cw = 6%, and 3.8 at Cw = 4%. Obviously, an expected 3-month shelf-life required Cw < or = 5%.