In orchid conservation efforts aimed at reintroduction, seeds are preferred because they conserve the genetic diversity that can ensure the success and sustainability of the reintroduced population. Germinating seeds together with the species-specific mycorrhizal fungi could improve the success of seed-based conservation programs, both in in situ germplasm conservation and in reintroduction efforts. However, this requires the isolation, identification and germination enhancement testing of the fungi and a good understanding of the factors that determine the symbiotic association between the orchid seeds and the fungi. Few studies have focused on developing such techniques for the epiphytes that constitute the majority of orchids.
Prof. GAO Jiangyun and his research team of Xishuangbanna Tropical Botanical Garden (XTBG) reported on the isolation, identification, and testing of the effect of symbiotic fungi and light on the success of each seed germination stage in an epiphytic orchid, Dendrobium aphyllum (Roxb.) C.E.C. Fischer. The investigation was conducted as part of a conservation research program focusing on preventing the extinction of rare and endangered orchid species.
Using fungal isolates from in situ seed baiting (using seeds wrapped in muslin cloth and placed in the habitat of the adult plants ) near adult D. aphyllum plants, they tested the following hypotheses: (1) The species-specific mycorrhizae extracted from the protocorms developed near the adult D. aphyllum should have a greater impact on the success of germination and subsequent stages of seed development than fungi isolated from other orchids plants, or germination in the absence of symbiotic fungi. (2) In addition to the fungi, the presence of light should further enhance seed germination and developmental success of D. aphyllum orchid seedlings. (3) The facilitation from fungi and light for seed germination may be seed developmental stage-specific.
They found that D. aphyllum orchid seed germination enhancement due to light availability and supporting fungal inoculum was germination stage-specific and that fungal enhancement of germination could be species-specific. In addition to gaining a better understanding of the biology of orchid symbiotic seed germination, those findings had a broader impact of improving seedling generation for conservation and reintroduction programs aimed at reducing the wild collection pressure on that species.
The study was the first to report on culturable mycorrhizal fungi isolated from germinated protocorms of D. aphyllum and the first to empirically test whether the fungus was stage-specific in enhancing germination.