Horizontal gene transfer from custard apple plant to Metarhizium anisopliae strains

Entomopathogens provide an effective strategy for the control of insect pests in agriculture. In our search for indigenous virulent strains of entomopathogenic Metarhizium anisopliae, we observed that the strains isolated from soils associated with custard apple (Annona squamosa), a plant not affected by chewing insects, have higher virulence (> 90% mortality, at one tenth the concentration, in insect bioassay) than strains isolated from fields with tomato plants (Solanum lycopersicum), vulnerable to insect attacks. These highly virulent strains lose most of their virulence during repeated subculture on an artificial medium, but the virulence is restored once they establish themselves as endophytes in custard apple. Here we report the evidences to show that such higher virulence exhibited by the M. anisopliae strains isolated from custard apple fields is due to the horizontal transfer of insecticidal traits from the custard apple plant to the endophyte. Further, these horizontally transferred genes are switched off under repeated subculturing and the strains isolated from tomato fields lack these genes.