Mycorrhizal fungi play a vital role in the life history of orchids, from early germination to mycorrhizal association in adults. Arundina graminifolia is a terrestrial orchid widely distributed in subtropical and tropical Southeast Asia at elevations. However, the mycorrhizal symbiosis of A. graminifolia remains largely unknown. 

Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) and Yunnan University used one population of A. graminifolia to test how seed germination was impacted fungi isolated from advanced seedlings versus from adults. They also tested how seed germination of orchid was influenced by mycorrhizal rhizoctonias versus other non-mycorrhizal endophytes. 

The researchers isolated fungi and identified them by ITS sequencing, and tested for their impact on seed germination, protocorm formation, and development of advanced seedlings (emergence of first leaf) in vitro. 

By comparing the fungus assemblages in roots and advanced seedlings, and by testing their effects on the germination sequence in A. graminifolia, the researchers added support to the growing literature showing that, in some species, fungal diversity decreases with advanced seedling development before increasing again at adulthood (bottleneck in diversity). 

As a result, best germination can sometimes be achieved in orchid species with a fungal partner specifically isolated from early life stages. 

“Considering this development-dependent specificity, our results suggest the use, whenever possible, of fungi isolated by the seed baiting technique in situ or ex situ, or even from young orchid seedlings (even protocorms) collected in the wild, with a view to ex situ orchid conservation practices”, said the researchers. 

The study entitled “Are fungi from adult orchid roots the best symbionts at germination? A case study” has been published online in Mycorrhiza.