An Electron-Microscope Study of Host Penetration and Early Stages of Haustorium Formation of Peronospora parasitica (Fr.) Tul. on Cabbage Cotyledons

Penetration of the epidermis of cabbage cotyledons and haustorium development by Peronospora parasitica within 12 hours of spore germination was studied by means of the electron microscope. The ultrastructure of appressoria, penetrating hyphae, developing haustorium and host cells associated with the invading parasite are described. The mechanism of penetration and the terminology concerned with the ultrastructure of host-parasite interfaces are discussed.