Fungi from orchid mycorrhizas

Abstract

An important step in studies of orchid mycorrhizas is identification of the mycobionts (Table 4-1; epithets may have changed since reported). Generally, these have been shown to be members of the Subdivision Basidiomycotina (frequently referred to informally using an old Class name, ‘basidiomycetes’) which can form characteristic intracellular masses of hyphae, called pelotons, within root or rhizome cortical tissue of orchids. A number of species in the Subdivision Ascomycotina (‘ascomycetes’) and the Fungi Imperfecti (‘molds, yeasts and pycnidial fungi’) are common associates of orchid roots and mycorrhizas, but their biological role is unknown. In most studies of orchid mycorrhizas, the non-basidiomycete isolates have been discounted, and accurate reports of the diversity of these fungi among the community of endophyte and rhizosphere organisms are almost non-existent (Richardson and Currah, 1995; Salmia, 1988). However, the Ascomycotina, Fungi Imperfecti and other microorganisms are involved in a wide range of nutrient-gathering and sequestering roles and can have a significant influence on the competitive abilities of phytobionts (Kucey and Leggett, 1989; Read, 1991; Wilkinson et al., 1989). Some of the hitherto discounted ascomycete and mold associates may be as important to orchids in nature as the basidiomycetes that form the distinctive intracellular pelotons.

This chapter is dedicated to the memory of Dr Gaku Masuhara.

The literature review pertaining to this chapter was concluded in August 1994, and the revised version was accepted in May 1995.