EFFECT OF CARBOHYDRATE TYPE AND CONCENTRATION ON POLYHYDROXY ALCOHOL AND TREHALOSE CONTENT OF CONIDIA OF 3 ENTOMOPATHOGENIC FUNGI

The entomopathogenic fungi Beauveria bassiana, Metarhizium anisopliae and Paecilomyces farinosus were cultured on solid agar media containin g different carbohydrate components (glycerol, glucose, trehalose or s tarch) at concentrations of less than or equal to 142.7 g added carbon l(-1) for 30 d at 25 degrees C. The water activity (a(w)) of the medi a ranged from 0.925 to 0.998. Growth of M. anisopliae and P. farinosus was stimulated between 0.975 and 0.995 a(w) on glucose media and that of P. farinosus at 0.975 a(w) on glycerol media. At < 0.970 a(w), gro wth of each fungal species was significantly reduced (P < 0.05). Polyh ydroxy alcohols (polyols) and trehalose were extracted from conidia pr oduced on different media and quantified using HPLC. Total polyol cont ent of conidia produced on glucose media varied between 5.2 and 52.2 m g g(-1) for B. bassiana, 77.3 and 90.3 mg g(-1) for M. anisopliae. and 26.7 and 76.1 mg g(-1) for P. farinosus. The amounts of specific poly ols in conidia varied significantly from media of different glucose co ncentrations. Mannitol was the predominant polyol in conidia of all th ree species, with conidia of M. anisopliae, for example, containing as much as 75.2 mg mannitol g(-1) when cultured on glucose media. The am ount of the lower molecular mass polyols glycerol and erythritol was g reater in conidia produced on glucose media with > 50.0 g added carbon l(-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 l(-1), depending on spe cies. Conversely, conidia of B. bassiana and P. farinosus contained ma ximum amounts of trehalose (less than or equal to 23.5 mg g(-1)) when produced on glucose media with < 50.0 g added carbon l(-1), and trehal ose content was considerably less at higher glucose concentrations. Th ere were accumulations of glycerol and erythritol in conidia of all th ree species when grown on glycerol media with > 25.0 g added carbon l( -1); conidia of B. bassiana contained up to 154.0 mg glycerol plus ery thritol g(-1). When B. bassiana and P. farinosus were grown on trehalo se media, conidia contained up to 222.1 mg trehalose g(-1). By contras t, conidia of M. anisopliae contained < 17.0 mg trehalose g(-1) under all conditions tested. The water availability of solutions of differen t polyols is discussed in relation to their potential to act in osmoti c adjustment during germination. The ability to manipulate polyol and trehalose content of fungal propagules may be critical in enhancing th e storage life and efficacy of biological control agents.