Saprophytic Growth of Arbuscular Mycorrhizal Fungi

Strictly speaking the title of this chapter is a contradiction. If “saprophytic growth” is growth exhibited by an organism in a free-living status, it is obvious that this term cannot apply to arbuscular mycorrhizal fungi (AMF) as none of the 130 species of AMF have yet been successfully cultured axenically. These fungi have a low, or negligible, saprophytic ability and can apparently produce viable propagules only upon the biotrophic colonization of a susceptible host root. They are thus considered physiologically obligate symbionts and the related literature reflects the failure to grow them on synthetic media (Azcon-Aguilar and Barea 1992). There are descriptions, however, of limited saprophytic development of AMF which takes place either in soil, prior to any contact with the host root, or even “in vitro” (Azcon-Aguilar and Barea 1985; Koske and Gemma 1992; Giovannetti et al. 1996). It is this saprophytic growth which will be discussed in this chapter.