Comparative Tolerances of Various Beauveria bassiana Isolates to UV-B Irradiation with a Description of a Modeling Method to Assess Lethal Dose
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- Huang, BF. & Feng, MG. Mycopathologia (2009) 168: 145. doi:10.1007/s11046-009-9207-7
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The tolerances of 20 Beauveria bassiana isolates derived from host insects worldwide to UV-B irradiation were assessed quantitatively in multi-dose bioassays. Conidial suspensions of the isolates smeared on glass slides were exposed to the gradient UV-B doses of 0.1–1.6 J cm−2 (D), which generated from 0.75 to 10.17 min irradiation of weighted 312-nm wavelength at 2.0–2.61 mW cm−2. Irradiated conidia were then incubated for 24 h at 25°C under saturated humidity. The ratio of germination at each dose over that in the blank control was defined as survival index (Is). For all isolates, the Is − D observations fit well with the survival model Is = 1/[1 + exp(a + bD)] (0.94 ≤ r2 ≤ 0.99) generated widely spanned lethal doses of 0.154–0.928, 0.240–1.139, and 0.383–1.493 J cm−2 for their losses of 50%, 75%, and 95% viabilities, respectively. These were far below the solar UV-B dose of 2.439 J cm−2 measured in a sunny day during the summer. The large variation of UV-B tolerance among the isolates indicates a necessity to select UV-tolerant candidates for formulations applied to insect control during summer. The highly efficient bioassay method was developed to measure accurately the UV-B tolerances of fungal biocontrol agents as lethal doses.