The effect of crucifer epicuticular waxes and leaf extracts on the germination and virulence of Metarhizium anisopliae conidia

Leaves of members of the Cruciferae influence the germination of the entomogenous fungus Metarhizium anisopliae. The percentage germination of conidia on reconstituted epicuticular waxes of oilseed rape, Chinese cabbage, and turnip was influenced by the solvent used, the plant species, and the age of the leaf. The epicuticular waxes contain a mixture of stimulatory and inhibitory compounds. Germination was more rapid and greater on the surfaces of dewaxed than intact leaves suggesting that epicuticular waxes contain fungistatic compounds and/or act as a barrier to the leaching of nutrients. Surface leachates and soluble extracts of leaves increased percentage germination of conidia and the virulence of M. anisopliae to the mustard beetle, Phaedon cochleariae. Plant extracts stimulated germination more than yeast or starch extract. Formulation of conidia in leachates or leaf extracts increased the virulence of M. anisopliae. Germination increased on insect cuticle that were pretreated with leaf extracts/leachates, suggesting that the insect cuticle will adsorb or sequester nutrients.