Spore Swelling, Germination, and Germ Tube Formation in Axenic Culture Among four Species of Piptocephalis

Abstract

The nutritional requirements for spore swelling, germination, and germ tube formation in axenic culture were compared among four species of Piptocephalis. The spores of P. lepidula did not require exogenous nutrients for swelling, germination, or germ tube formation, although best germ tube elongation occurred on media containing selected nitrogen sources. In contrast, significant swelling, germination, and germ tube elongation of P. digitata and P. xenophila spores only occurred on media containing orange juice or yeast extract. Piptocephalis virginiana spores swelled on several media that did not support germination or germ tube formation. Best germ tube elongation by P. virginiana occurred on a medium containing yeast extract. Species of Piptocephalis, members of the Piptocephalidaceae (Mucorales), are biotrophic-haustorial mycoparasites. Although limited axenic growth and reproduction of some species of Piptocephalis have occurred on agar media (7), no member of this genus has yet been maintained in continuous axenic culture (2, 7). In fact, spore swelling, germination, and germ tube development by Piptocephalis digitata nomen nudum, P. unispora Benjamin, P. virginiana Leadbeater and Mercer and P. xenophila Dobbs and English only occurred on media containing complex constituents, a host fungus, or filtrates from host and nonhost fungi (1, 2, 3, 4, 5). In preliminary work in this laboratory, spores of P. lepidula (Marchal) Benjamin were observed to germinate readily. Since this suggested spores of this fungus differed from those of other species of Piptocephalis (3, 4, 5), spore swelling, germination, and germ tube elongation were compared in axenic culture among four Piptocephalis species. This report presents the results of those comparisons.