An amalgam of pathogenic and beneficial endophytic fungi colonizing four Dendrobium species from Meghalaya, India.

Endophytic fungi are known to play an important role in driving the evolution of plants by conferring adaptational advantages to their host through the production of secondary metabolites and phytohormones. In this study, we evaluated the diversity and phylogenetic relationship of endophytic fungal communities from four Dendrobium species viz., Dendrobium chrysanthum, Dendrobium heterocarpum, Dendrobium hookerianum, and Dendrobium longicornu of Meghalaya, India. A total of 51 culturable endophytic fungi were isolated from the four selected orchid species. The isolates were identified based on nuclear large subunit sequences into 33 species. Approximately 91% of the isolates showed affinity to Ascomycetes, while 9% of the isolates showed BLAST search similarity to Basidiomycetes. The most common genera were Trichoderma and Xylaria. The most prevalent genera were Fusarium, which was detected in all the four Dendrobium species followed by Diaporthe, which was present in three Dendrobium species viz., D. chrysanthum, D. hookerianum, and D. heterocarpum. The Shannon index value of endophytic fungal communities was the highest in D. chrysanthum (2.66), while D. longicornu (1) had the highest Evenness index. The present study revealed that endophytic fungi in these orchids are an amalgam of pathogenic and beneficial fungi, which have, at the least, switched their lifestyle to asymptomatic endophyte in their host. To our knowledge, this is the first such report on the diversity of endophytic fungi in the four selected Dendrobium species from Meghalaya, India.

Compatible fungi, suitable medium, and appropriate developmental stage essential for stable association of Dendrobium chrysanthum.

Establishment of symbiotic association at the appropriate developmental stage helped maintain continued growth which is vital for the long-term ex vitro survival of the orchid. In the present study, symbiotic association was carried out using different developmental stages of Dendrobium chrysanthum and pathogenic Rhizoctonia isolates (obtained from orchids and non-orchid hosts) in different culture media. Isolate 2162 supported highest symbiotic germination on OMA-S (oat meal agar medium without nutrients + sucrose), whereas, stable symbiotic association with plantlets was obtained with isolate 4634 on OMA-NC (oat meal agar medium + cellulose). Isolate Dc-2S2 obtained from the host plant did not promote seed germination nor did it form association with protocorms or plantlets. This study, for the first time identifies a combination of compatible fungal isolate, suitable culture medium, and appropriate developmental stage at which symbiotic association in vitro can be deemed successful for the medicinally important orchid, D. chrysanthum.