Promoting effect of orchid mycorrhizal fungi Epulorhiza isolates on seed germination of Dendrobium orchids

Abstract

In order to germinate in nature, orchid seeds depend on mycorrhizal fungi to provide them carbohydrate, vitamins and growth factors for germination. The benefit of orchid mycorrhiza can potentially be applied to commercial propagation of orchids. This study compared the effectiveness of five isolates of the orchid mycorrhizal fungus Epulorhiza sp. (= anamorph of Tulasnella) in promoting seed germination and protocorm development of four species of Dendrobium Sw. (Orchidaceae). Orchid seeds sown on Murashige and Skoog (MS) medium, oat meal agar (OMA) or OMA inoculated with one of the five fungal isolates were kept in dark at 25°C for 2 weeks and then in a 16-h-light/8-h-dark cycle for 7 weeks. The promoting effects of different fungal isolates on seed germination of each orchid species were shown to be unequal. The isolates, Da-KP-0-1 and Ps-KT-0-1, were most effective in promoting seed germination and protocorm development of Dendrobium pulchellum Roxb. ex Lindl. and Dendrobium crepidatum Lindl. & Paxton, whereas the isolates Pv-PC-1-1 and Da-KP-0-1 were best for seed germination and protocorm development of Dendrobium findlayanum E.C. Parish & Rchb. f. The seeds of these three orchid species co-cultured with compatible fungi developed more rapidly than asymbiotic seeds of the same species sown on OMA and as rapidly as the ones sown on MS medium. For Dendrobium crystallinum Rchb. f., the average developmental stages of seeds sown on MS medium or OMA inoculated with the most effective fungal isolates were not significantly different from those sown on OMA, probably due to food reserve in the seeds. Randomly sampled protocorms were examined microscopically to confirm the presence of mycorrhizal fungi. All Epulorhiza isolates used in this study, except for the isolate Cs-QS-0-1, could form pelotons in the studied orchids.