Highly compatible Epa-01 strain promotes seed germination and protocorm development of Papilionanthe teres (Orchidaceae)

Symbiotic seed germination serves as a preferred method for orchid multiplication related to conservation and reintroduction programs, which involves isolation, identification, and germination-enhancing testing of symbiotic fungi. This study uses seeds of Papilionanthe teres, a locally endangered and medicinally valuable epiphytic orchid, to attract germination-enhancing fungi on its four host plants. Only one common and highly compatible fungus (Epa-01 strain, Epulorhiza sp.), isolated from seed baiting near three host plants (Averrhoa carambola, Lagerstroemia villosa, Callistemon rigidus), enhanced seed germination by more than 80 % and promoted protocorm development to reach stage 5 (with two leaves). Seeds cocultured with the Epa-01 strain and oat meal agar medium significantly outperformed in germination and growth speed compared with those cocultured with asymbiotic germination medium only, indicating that symbiotic seed germination is an effective method for P. teres seedling production. Bark substrate types have profound effects on symbiotic seed germination and protocorm development possibly due to different abundance and growth vitality of the Epa-01 strain on the four host plants. A significant difference was found in the developmental speed of symbiotic seeds between A. carambola and the other three host plants under ex situ and ex vitro seed germination treatments (all P < 0.05). The results suggest that in situ seed baiting may be used to effectively capture germination-enhancing fungi in epiphytic orchids, and testing the effects of bark substrate types on seed germination and protocorm development contributes to selecting appropriate host plants for its reintroduction into natural habitats.