Is Spizellomyces Punctatum a Parasite or Saprophyte of Vesicular-Arbuscular Mycorrhizal Fungi?

Abstract

Spizellomyces punctatum has been reported to be a mycoparasite on spores of vesiculararbuscular mycorrhizal fungi, and studies were undertaken to determine whether this species attacked viable or non-viable Gigaspora margarita azygospores incubated in sterile sand on nylon sieves and inoculated with zoospores of the fungus. (1) Spizellomyces puntatum mostly attacked non-germinated azygospores. (2) Inoculation of G. margarita azygospores with zoospores of S. punctatum did not significantly reduce the incidence of azygospore germination. (3) Pre-killing of azygospores with propylene oxide or heat greatly increased colonization by S. punctatum. (4) Water soluble exudates from propylene oxide-killed azygospores chemotactically attracted more S. punctatum zoospores than exudates from healthy azygospores. (5) High populations of the chytrid did not reduce infection or growth response by G. margarita when a zoospore suspension of S. punctatum was mixed with VAM inoculum and added to cotton plants in the greenhouse. Infection and growth response of citrus by Glomus fasciculatum similarly were not reduced. This evidence suggests that S. punctatum is primarily a saprophyte which attacks non-viable spores of VAM fungi.