Growth and formation of true conidia by Metarhizium flavoviride in a simple liquid medium

Abstract

In shaken liquid culture on media containing sucrose and brewers' yeast or peptone, 5 isolates of Metarhizium flavoviride from acridoid hosts produced submerged sporogenous cells and spores morphologically indistinguishable from aerial phialides and conidia. Submerged conidia produced by IMI 330189 were 4·6 × 2·6 m, within the size range described for M. flavoviride var. minus aerial conidia. Submerged hyphae and conidia contained green pigment. One of four isolates of M. anisopliae from acridids and other insects produced non-pigmented hyphal bodies (‘blastospores’) by budding under similar conditions. Production of vegetative biomass in M. flavoviride was enhanced by increasing the concentration of either the carbohydrate or the organic nitrogen component. The onset of conidiation was controlled both by the ratio of yeast to sucrose and the quantity of yeast in the medium. Increasing the yeast concentration delayed the onset of conidiation, suggesting that this was triggered when the nitrogen component was depleted. After initiation, conidiation was limited by carbohydrate availability. More than 1·5 × 109 conidia ml−1 were formed after 7 d in media containing 20 g yeast and 20 g sucrose or 30 g yeast and 30 g sucrose l−1.