Characterization of Metarhizium species and varieties based on molecular analysis, heat tolerance and cold activity

Éverton K. K. Fernandes
Chad A. Keyser
J. P. Chong
Drauzio E. N. Rangel
Mark P. Miller
Donald W. Roberts, Utah State Univeristy


Aims: The genetic relationships and conidial tolerances to high and low temperatures were determined for isolates of several Metarhizium species and varieties. Methods and Results: Molecular-based techniques [AFLP and rDNA (ITS1, ITS2 and 5Æ8S) gene sequencing] were used to characterize morphologically identified Metarhizium spp. isolates from a wide range of sources. Conidial sus- pensions of isolates were exposed to wet heat (45 ± 0Æ2°C) and plated on potato dextrose agar plus yeast extract (PDAY) medium. After 8-h exposure, the iso- lates divided clearly into two groups: (i) all isolates of Metarhizium anisopliae var. anisopliae (Ma-an) and Metarhizium from the flavoviride complex (Mf) had virtually zero conidial relative germination (RG), (ii) Metarhizium anisopliae var. acridum (Ma-ac) isolates demonstrated high heat tolerance (c. 70–100% RG). Conidial suspensions also were plated on PDAY and incubated at 5°C for 15 days, during which time RGs for Ma-an and Ma-ac isolates were virtually zero, whereas the two Mf were highly cold active (100% RG). Conclusions: Heat and cold exposures can be used as rapid tools to tentatively identify some important Metarhizium species and varieties. Significance and Impact of the Study: Identification of Metarhizium spp. cur- rently relies primarily on DNA-based methods; we suggest a simple tempera- ture-based screen to quickly obtain tentative identification of isolates as to species or species complexes.