Entomopathogenic fungus Akanthomyces muscarius (Hypocreales: Cordycipitaceae) strain IMI 268317 colonises on tomato leaf surface through conidial adhesion and general and microcycle conidiation

The entomopathogenic fungus Akanthomyces muscarius strain IMI 268317, previously known as Lecanicilliummuscariumand Verticillium lecanii, is currently used as a microbial insecticide to protect tomatoes from serious leaf-inhabiting pests in greenhouses. However, its persistence on tomato leaves has been unidentified. Understanding the events and processes of phyllosphere colonisation by this strain should help in developing its practical applications. This study assessed the epiphytic abilities of this strain on tomato leaves in humid conditions, simulating closed greenhouse environments. Conidia applied on tomato leaflets strongly adhered 12 h after inoculation. The mucilage-like materials were found around the germinated conidia after 3 days after inoculation (dpi), which possibly strengthened the adhesion. A total of 15% of conidia germinated at 3 dpi, of which 2% formed typical conidium or an enlarged structure on germ-tube tips. Many conidia were produced on phialide tips that branched from elongated hyphae at 7 dpi; however, invasion into leaf tissue was not observed. On the leaflets, inoculated conidia suspensions of 1 × 10⁵ and 1 × 10⁶ conidia/mL, colony forming units increased 52.6 and 8.8 folds from 0 to 14 dpi, respectively. These results suggested that A. muscarius strain IMI 268317 has high epiphytic abilities on tomato leaflets in a humid condition.