MANIPULATION OF INTRACELLULAR GLYCEROL AND ERYTHRITOL ENHANCES GERMINATION OF CONIDIA AT LOW WATER AVAILABILITY

The insect pathogens Beauveria bassiana, Metarhizium anisopliae and Pa ecilomyces farinosus can be effective biocontrol agents when relative humidity (RH) is close to 100%. At reduced water availability, germina tion of propagules, and therefore host infection, cannot occur. Cultur es of B. bassiana, M. anisopliae and P. farinosus were grown under dif ferent conditions to obtain conidia with a modified polyol and trehalo se content. Conidia with higher intracellular concentrations of glycer ol and erythritol germinated both more quickly and at lower water acti vity (a(w)) than those from other treatments. In contrast, conidia con taining up to 235.7 mg trehalose g(-1) germinated significantly (P < 0 .05) more slowly than those with an equivalent polyol content but less trehalose, regardless of water availability. Conidia from control tre atments did not germinate below 0.951-0.935 a(w) (= 95.1-93.5% RH). In contrast, conidia containing up to 164.6 mg glycerol plus erythritol g(-1) germinated down to 0.887 a(w) (= 88.7% ph). These conidia germin ated below the water availability at which mycelial growth ceases (0.9 30-0.920 a(w)). Germ tube extension rates reflected the percentage ger mination of conidia, so the most rapid germ tube growth occurred after treatments which produced conidia containing the most glycerol and er ythritol. This study shows for the first time that manipulating polyol content can extend the range of water availability over which fungal propagules can germinate. Physiological manipulation of conidia may im prove biological control of insect pests in the field.