Symbiotic Germination of Some Australian Terrestrial Orchids

Abstract

SUMMARY In symbiosis tests on an agar medium with powdered cellulose as carbon source, isolates of several species of Tulasnella and of Ceratobasidium cornigerum were compared on seven species of Thelymitra and two each of Diuris and Pterostylis. The Pterostylis species were stimulated to germinate only by Ceratobasidium cornigerum, the Diuris species only by Tulasnella calospora but, in general, the Thelymitra species were stimulated by more than one species of Tulasnella, but not markedly by Ceratobasidium cornigerum. These results correlate well with specificities noted in isolations from the roots of mature orchids of these genera in nature. It was found that different isolates of Tulasnella calospora differed markedly in the efficiency with which they stimulated germination of the species of Diuris and Thelymitra. The most efficient isolates were not necessarily those isolated from these orchids.

Nutritional Requirements of Orchid Endophytes

“…Ungerminated seeds near to, or in contact with, the fungus never germinate or grow any more rapidly than those in control axenic cultures. Furthermore, many of the reports of such effects are actually referring to, and measuring growth of, the protocorms rather than germination of the seed, especially where specific effects of certain fungi may occur (Warcup, 1973).…”

Indução in vitro da germinação de sementes de Oncidium flexuosum (Orchidaceae) por fungos micorrízicos rizoctonióides

“…A especificidade da associação micorrízica em orquídeas é ainda fonte de controvérsia, visto que, enquanto alguns trabalhos demonstram a existência de especificidade entre fungo e planta (Warcup, 1971;1973;1981), outros demonstram a baixa ou, até mesmo, a inexistência de especificidade (Hadley, 1970;Deutsch, 2001;Stewart & Zettler, 2002). Além da dificuldade de identificação das espécies de fungos rizoctonióides comumente isolados de raízes micorrizadas de orquídeas, a avaliação de trabalhos sobre especificidade é ainda dificultada pela variabilidade de métodos de isolamento empregados, pelos diferentes estádios de desenvolvimento dos hospedeiros estudados e pela não-correspondência entre experimentos de germinação de sementes em condições naturais e in vitro (Andersen & Rasmussen, 1996).…”

Dark septate endophytes: a review of facultative biotrophic root‐colonizing fungi

“…Duddridge & Read (1984) and Duddridge (1986) demonstrated a change in the behaviour of ectomycorrhizal fungi in the presence of exogenous carbohydrate. The nutritional status of the fungal endophyte might therefore be an explanation for the controversial earlier results : and Stoyke & Currah (1993) used a growing medium with readily available carbohydrates, double-strength MMN (Marx & Zak, 1965) and cellulose agar (Warcup, 1973), respectively. By contrast, O'Dell et al (1993 used a method in which the seedlings were grown in a ' growth pouch ' to which nutrients, but no carbohydrates, were added.…”