Nuclear Events During Germination and Appressorial Formation of the Entomopathogenic Fungus Zoophthora Radicans (Zygomycetes: Entomophthorales)

Conidial germination, appressorial formation, and secondary sporulation in Zoophthora radicans occurred independently of DNA replication and nuclear division. Video-image analysis combined with epifluorescence microscopy showed that at 18 hr postinoculation, approximately 10% of germlings had undergone the first DNA duplication and nuclear division and that 20% of germlings had formed appressoria. Hydroxyurea, an inhibitor of DNA synthesis, prevented DNA replication and nuclear division but allowed production of germ tubes and appressoria. Actinomycin D, an inhibitor of RNA synthesis, totally inhibited germination at concentrations above 10ug/ml. At lower concentrations, actinomycin D allowed formation of germ ube and appressoria in a dose-dependent fashion. However, even at the lowest concentration tested (1ug/ml), nuclear division and formation of penetration hyphae were prevented. Formation of secondary conidia and capilli-conidia was also independent of nuclear division but was totally inhibited by drugs blocking RNA or protein synthesis. The implications of differentiation without prior nuclear division are discussed