Physiological and phylogenetic variability of Mexican Metarhizium strains

Metarhizium Sorokin is a wide spread entomopathogenic fungal genus that is also a root symbiont and some isolates may be potentially useful in agriculture applications. Physiological variations applicable in biological control have not been fully evaluated in Mexican strains. This study identified 30 strains from different insect hosts and states of Mexico selected because they represent the main sugar cane and corn plantations of the country. Their thermotolerance profiles (8, 15, 28 and 35 °C), insect virulence (LT50 in Galleria mellonella (Linnaeus) (Lepidoptera: Pyralidae) larvae), possible association with plant roots, and phylogenetic placement (using 5′TEF, IGS sequence information, and RFLP analysis) were assessed. Results showed no cold-active strains and most showed restricted growth at 35 °C. Insect virulence bioassays against G. mellonella showed highly virulent strains. Most of the strains showed an ability to associate with roots of Phaseolus vulgaris (Burkart) (Fabales: Fabaceae). RFLP analysis with 5′TEF and Pr1 revealed three distinct genetic groups. Phylogenetic analysis identified the 30 strains as Metarhizium anisopliae. (Metchnikoff) Sorokin, M. robertsii (J.F. Bisch., Rehner & Humber), M. guizhouense (Q. T. Chen & H. L. Guo), or M. pinghaense (Q.T. Chen & H.L. Guo), as well as two strains that belong to a new clade (Metarhizium sp. indet. 1). These data demonstrate the complexity of Metarhizium species and the need to study their physiological and phylogenetic aspects for a more adequate assessment of their potential use in agricultural systems.