The effect of storage environment on the longevity of conidia of Beauveria bassiana

The effect of air-dry storage environment on the longevity of conidia from seven isolates of Beauveria bassiana produced at different times and locations was determined by estimating the parameters of a viability equation. Conidia were stored hermetically at six to II moisture contents between 2.3 and 32.0% with one (50 +/- 0.5 degreesC) to five constant temperatures (10, 20, 30, 40 and 50 +/- 0.5 degrees) for various periods up to 372 d and then tested for viability. All isolates behaved similarly (P > 0.25) in terms of the relative effect of moisture content (C-W) and temperature (C-H and C-Q) on conidial longevity; common values were C-W = 3.05 (SE = 0.07), C-H = 0.0293 (SE = 0.0078), and C-Q = 0.00081 (SE = 0.00011). Estimates of the low-moisture-content limit to the negative logarithmic relation between conidial moisture content and longevity were 4.6 and 5.0% at 50 degrees and 40 degrees, respectively, for isolate 198-1140ss, and 5.2 and 5.1% moisture content, respectively, for isolate 197-1111. Absolute longevity (K-E) varied considerably (P < 0.005) among isolates, even within an isolate when conidia were produced at different locations. Among the eight samples of seven isolates, two cohorts were identified with respect to K-E (P < 0.005): conidia of three isolates which were produced at Ascot had a common estimate of K-E of 6.696 (SE = 0.170), whereas those produced at Nairobi or Carolina provided a lower estimate (6.203, SE = 0.029). This difference in K-E means that for any given viability period in any given environment, the conidia produced in Ascot provided about three times the longevity of the other samples.