Host-Parasite Relations in a Mycoparasite. VII. Light and Scanning Electron Microscopy of Interactions of Piptocephalis virginiana with Host and Nonhost Species

SUMMARYSpores of the mycoparasite Piptocephalis virginiana on germination usually produced two germ tubes. The germ tube nearest to a host hypha continued to grow and made contact with it. The tip of the germ tube in contact with the host formed an appressorium. Further events of parasitic infection depended on the nature of the host. In compatible interaction with a susceptible host, Choanephora cucurbitarum, the parasite penetrated the host cell wall without any apparent reaction of the host and formed a slender haustorium. Interaction with a resistant host, Phascolomyces articulosus, resulted in the development of host cell wall thickening at the site of penetration which probably arrested the further advance of the parasite. A marked difference between the penetration sites on the susceptible and resistant hosts was revealed by scanning electron microscopy. The parasite germinated equally well in the presence of host and nonhost species, but it neither made contact nor attempted penetration of hypha of a nonhost, Linderina pennispora.