Diversity and Antimicrobial and Plant-Growth-Promoting Activities of Endophytic Fungi in Dendrobium loddigesii Rolfe

Endophytic fungi are ubiquitously distributed in orchids and have a great impact on the host plant. The diversity of endophytic fungi in the medicinal orchid Dendrobium loddigesii Rolfe was investigated and their bioactivities in microbe and plant growth were explored here. Endophytic fungi were identified by using morphological and molecular biological methods. Antimicrobial activity was determined by a standard disk assay. Activity in promoting plant growth was confirmed by root inoculation of endophytic fungi in seedling tray and pot experiments. Overall, 48 isolates were isolated from D. loddigesii and identified to belong to 18 genera, with Fusarium and Acremonium being the most dominant populations. A total of 17 isolates belonging to 9 genera were screened for their antimicrobial activity, and Fusarium spp., 8 of the 17 isolates, was also the dominant population. In the seedling tray experiment, two isolates, one of Fusarium named DL26 and the other of Pyrenochaeta named DL351, were shown to enhance plant growth in alder bark-humus medium, and the latter displayed weak activity against Bacillus subtilis (As 1.308) and Aspergillus fumigatus (As 3.2910). In the pot experiment, after inoculation of DL26 and DL351, five out of seven media were fit for plant-endophyte symbionts. Medium #1 of red brick fragments and sphagna was optimal in accelerating plant growth. In conclusion, a great diversity of endophytic fungi in D. loddigesii was first confirmed in a considerable proportion of antimicrobial isolates. Furthermore, two endophytes exhibited the ability to enhance plant growth although their activities were influenced by the growth media.