Symbiotic propagation of seedlings of Cyrtopodium glutiniferum Raddi (Orchidaceae)

Abstract

In nature, orchid seeds obtain the nutrients necessary for germination by degrading intracellular fungal structures formed after colonization of the embryo by mycorrhizal fungi. Protocols for asymbiotic germination of orchid seeds typically use media with high concentrations of soluble carbohydrate and minerals. However, when reintroduced into the field, seedlings obtained via asymbiotic germination have lower survival rates than do seedlings obtained via symbiotic germination. Tree fern fiber, the ideal substrate for orchid seedling acclimatization, is increasingly scarce. Here, we evaluated seed germination and protocorm development of Cyrtopodium glutiniferum Raddi cultivated in asymbiotic media (Knudson C and Murashige & Skoog) and in oatmeal agar (OA) medium inoculated with the mycorrhizal fungus Epulorhiza sp., using non-inoculated OA medium as a control. We also evaluated the performance of tree fern fiber, pine bark, eucalyptus bark, corncob and sawdust as substrates for the acclimatization of symbiotically propagated plants. We determined germination percentages, protocorm development and growth indices at 35 and 70 days of cultivation. Relative growth rates and the effects of substrates on mycorrhizal formation were calculated after 165 days of cultivation. Germination efficiency and growth indices were best when inoculated OA medium was used. Corncob and pine bark showed the highest percentages of colonized system roots. The OA medium inoculated with Epulorhiza sp. shows potential for C. glutiniferum seedling production. Corncob and pine bark are promising substitutes for tree fern fiber as substrates for the acclimatization of orchid seedlings.

Characterization of seed germination and protocorm development of Cyrtopodium glutiniferum (Orchidaceae) promoted by mycorrhizal fungi Epulorhiza spp.

“…Consequently, it is essential to perform a screening test to identify the most efficient isolate. The obtainment of seedlings in advanced stage (stage 6) suggests that is possible to introduce seedlings ex vitro with higher survival rates, as demonstrated by Guimarães et al (2013). Here we describe anatomically the development of the protocorm of C. glutiniferum from seed to seedling, and confirm the maintenance of an association with the mycorrhizal fungi during this period.…”

“…The identification of Epulorhiza spp. as a suitable symbiont of C. glutinifurum permitted a second series of experiments on seed germination and seedling acclimatization, as performed by Guimarães et al (2013). These authors selected the Epulorhiza sp.…”

“…Mycorrhizal colonization and fungi consumption persist in orchid roots into adulthood, when the interaction serves an important role in orchid nutrition (Dearnaley 2007;Rasmussen & Rasmussen 2009). Inoculation with mycorrhizal fungi has been applied to in vitro symbiotic seed germination and orchid cultivation (Pereira et al 2011;Guimarães et al 2013), with promising applications in the propagation of ornamental (Pereira et al 2003a;2005a), endangered (Zettler & McInnis 1992;Zettler et al 2007), and medicinal orchids (Chang & Chou 2001;Tan et al 2014).…”

“…The degree to which tropical orchids utilize fungi is unclear, but we have attempted to understand the orchidmycorrhizal association in our studies by isolating and identifying fungal symbionts (Pereira et al 2003b;2005b;Valadares et al 2015), by germinating seeds of tropical orchids (Pereira et al 2005a;2011;Guimarães et al 2013) and by characterizing protocorm development. Histological studies have also contributed to understanding the mechanisms involved in the mycorrhizal association (Arditti 1992).…”

Isolation and characterization of mycorrhizal fungi in Cyrtopodium vernum Rchb. F. & Warm (Orchidaceae)

“…Inoculants of Epulorhiza sp. were used in the symbiotic germination and promotion of growth of Cyrtopodium glutiniferum Raddi (Guimarães et al, 2013), and inoculants of Rhizoctonia-like mycorrhizal fungi promoted greater survival of seedlings of Cymbidium aloifolium (L.) and Cymbidium giganteum Waal. Ex Lindl.…”