Early processes involved in host recognition by arbuscular mycorrhizal fungi.

Plant species that are hosts of non-arbuscular mycorrhizas were utilized to investigate the early processes involved in host recognition by arbuscular mycorrhizal fungi. The roots of plant hosts of ecto-, arbutoid and ericoid mycorrhizas, as well as those of non-mycorrhizal species, did not elicit the differential morphogenesis that occurred in the hyphae of Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe when challenged with the roots of its hosts. In the absence of this morphogenetic response, infection structures were not formed, any further step in the recognition process was hindered, and defence reactions did not occur. The ability of arbuscular mycorrhizal fungi to discriminate their specific hosts from alt other plant species through a recognition process is probably determined by chemical signals.