Genetic Differences in Allozymes and in Formation of Infection Structures Among Isolates of the Entomopathogenic Fungus Metarhizium Anisopliae
Journal of Invertebrate Pathology
In this study, we examined variation among isolates of the entomopathogenic fungus Metarhizium anisopliae in their ability to germinate and produce infection structures (appressoria) in different nutrient media. We also examined allozyme variation within and among 120 isolates of Metarhizium spp. Electromorph differences were noted and genotypic designations were assigned for eight loci encoding the following enzymes: glucose phosphate isomerase, glutamate dehydrogenase, glutamic pyruvic transaminase, glutathione reductase, malate dehydrogenase, phosphogluconate dehydrogenase, peptidase with glycyl leucine, and triosephosphate isomerase. Forty-eight distinct genotypic classes were found. Only the thirteen M. anisopliae var. majus isolates and an isolate of Metarhizium flavoviride possessed multibanded phenotypes characteristic of heterozygous genotypes. Three isolates were heterozygous at one locus, seven isolates at two loci, and four isolates at four loci. Based on the level of genetic similarities between the three recognized species (M. anisopliae, Metarhizium album, and M. flavoviriae) we report that isolates currently assigned as M. anisopliae are a strongly heterogenous array of multilocus genotypes that includes five varieties and two undescribed cryptic species. Genetic similarities provided evidence for geographical clustering. For example, Brazil and Colombia contain a common, widely dispersed genotypic class; eight additional classes are more locally distributed. Nutrient requirements for germination and appessorium formation were frequently host related, irrespective of genetic and geographical distance. Most of those lines of M. anisopliae var. anisopliae and var. majus isolated from scarabaeids germinated readily only in the presence of a crude protein/chitin product. Lines isolated from other coleopterans were much more adaptable and produced appressoria in yeast extract media. Unlike the majority of isolates from other hosts, lines isolated from Hemiptera usually germinated well in media containing glucose as the sole carbon source, and glucose allowed formation of appressoria. The role of selectable strain variations in the development of pathogen strategies is discussed.
St. Leger, R.J., B. May, L.L. Allee, D.C. Frank, R.C. Staples and D.W. Roberts. 1992. Genetic differences in allozymes and in formation of infection structures among isolates of the entomopathogenic fungus Metarhizium anisopliae. J. Invertebr. Pathol. 60: 89-101.