ISOLATION, IDENTIFICATION AND EVALUATION OF THE INFLUENCE OF Rhizoctonia-LIKE ENDOPHYTIC FUNGI ASSOCIATED WITH ROOTS OF Dendrobium thyrsiflorum REICHB.F. IN ANDRE ORCHID ON THEIR SEED GERMINATION

Abstract

Dendrobium thyrsiflorum is a valuable orchid species extensively exploited in Vietnam for medicinal and ornamental purposes. Isolating and evaluating the effects of endophytic fungi on D. thyrsiflorum could offer insights into the orchid-mycorrhizal fungus interactions. Using four isolation methods, this study obtained fourteen Rhizoctonia-like fungi from the roots of seedlings and protocorms of D. thyrsiflorum in Cat Tien National Park. Among these, five fungal isolates exhibited positive effects on seed germination when co-cultured on OMA medium. After 30 days, the seeds developed to stage 2 of the germination process, which was slower compared to the control seeds sown on 1/2 MS medium (stage 3). Mineral deficiency of the OMA medium may be the cause of hindered germination. Mineral supplementation by adding 1/10 MS to OMA medium facilitated seed development to stage 3 after 30 days, and stage 5 after 90 days of co-cultivation with fungal isolates TTP1C3 and F7C1. Furthermore, the presence of pelotons in the roots of seedlings co-cultured with TTP1C3 and F7C1 was observed. Molecular identification based on the nuclear ribosomal Internal Transcribed Spacer (ITS-DNA) region sequence revealed that the two target fungal isolates belonged to genus Hypoxylon and Daldinia. This is the first time that these fungal genera have been reported in Dendrobium. Although they cannot yet be considered specific Endomycorrhizae, these two strains show the potential to stimulate seed germination and embryo development, while also contributing to the enrichment of the endophytic fungal system of Dendrobium and supporting the conservation of this rare medicinal orchid germplasm.