Effect of carbohydrate type and concentration on polyhydroxy alcohol and trehalose content of conidia of three entomopathogenic fungi

Abstract

The entomopathogenic fungi Beauveria bassiana, Metarhizium anisopliae and Paecilomyces farinosus were cultured on solid agar media containing different carbohydrate components (glycerol, glucose, trehalose or starch) at concentrations of ≤ 142.7 g added carbon I-1 for 30 d at 25 °C. The water activity (aw) of the media ranged from 0.925 to 0.998. Growth of M. anisopliae and P. farinosus was stimulated between 0.975 and 0.995 aw on glucose media and that of P. farinosus at 0.975 aw on glycerol media. At 50.0 g added carbon I-1 than that in conidia produced at lower glucose concentrations. Conidia contained between 10.8 and 20.8 mg glycerol plus erythritol g-1 on glucose media with 142.7 g added carbon I-1, depending on species. Conversely, conidia of B. bassiana and P. farinosus contained maximum amounts of trehalose (≤ 23.5 mg g-1) when produced on glucose media with 25.0 g added carbon I-1, conidia of B. bassiana contained up to 154.0 mg glycerol plus erythritol g-1. When B. bassiana and P. farinosus were grown on trehalose media, conidia contained up to 222.1 mg trehalose g-1. By contrast, conidia of M. anisopliae contained < 17.0 mg trehalose g-1 under all conditions tested. The water availability of solutions of different polyols is discussed in relation to their potential to act in osmotic adjustment during germination. The ability to manipulate polyol and trehalose content of fungal propagules may be critical in enhancing the storage life and efficacy of biological control agents.