Isolation of <i>Metarhizium</i> spp. from rhizosphere soils of wild plants reflects fungal diversity in soil but not plant specificity

Understanding the abundance and diversity of fungal entomopathogens associated with plant species is critical for improving their field efficacy as microbial insecticides. <i>Metarhizium</i> is a cosmopolitan entomopathogenic fungus, with some species in this genus showing rhizosphere competencies. This study sought to determine the abundance and diversity of <i>Metarhizium</i> spp. in rhizosphere soils of wild plants in a field in Japan. <i>Metarhizium</i> spp. were detected in 76.2% of 151 rhizosphere soil samples collected from 41 plant species using a plating method. The mean density of <i>Metarhizium</i> spp. in rhizosphere soils was 1.2 × 10⁴ colony forming units/g soil [base 10 logarithm of the mean = 4.06 (S.D. = 0.88)]. There was no significant difference in the densities and detection rates between Asteraceae and Poaceae as well as among two aster and one grass species. The fungal isolates were identified as five species, of which <i>M. pingshaense</i> was the most frequently detected and abundant species. No significant specific associations were recognised between the isolated <i>Metarhizium</i> spp. and the examined aster and grass species. Our findings demonstrated the high occurrence and abundance of <i>M. pingshaense</i> in rhizosphere soils of wild plants at the sampling site irrespective of host plant taxa.