IN-SITU AND IN-VITRO SPECIFICITY BETWEEN RHIZOCTONIA SPP AND SPIRANTHES-SINENSIS (PERSOON) AMES VAR AMOENA (M BIEBERSTEIN) HARA (ORCHIDACEAE)

The relationships between the orchid Spiranthes sinensis (Persoon) Ame s. var. amoena (M. Bieberstein) Hara and Rhizoctonia spp. were investi gated in situ at germination and in adult plants. Seeds of the orchid placed in cotton gauze were buried at 210 sampling points in turf gras sland, the orchid habitat (in situ germination). Eight weeks later, pr otocorm development of the orchid was confirmed at 67 of the 210 sampl ing points. Isolation of fungi from protocorms showed that in situ ger mination was induced mainly by Rhizoctonia repens Bernard. Similarly, R. repens was the dominant mycorrhizal fungus isolated from roots of a dult plants. The number of adult plants within a radius of either 30 o r 50 cm of burial points did not influence seed germination. The distr ibution of Rhizoctonia spp. other than R. repens in the sample site wa s examined with a baiting method using buckwheat stems. Thirty-two iso lates consisting of binucleate Rhizoctonia anastomosis group (AG)-A, A GB, AG-G, and AG-I, R. solani Kuhn AG-4, Waitea circinata Warcup and: Talbot, which anastomozed with WAG-O and WAG-Z, and a multinucleate Rh izoctonia sp. were isolated. Three AG-G isolates were obtained from th e points at which protocorm development was induced by R. repens. Seed s of S. sinensis var. amoena were inoculated in vitro with these isola tes to test for symbiotic germination. Most Rhizoctonia spp. not assoc iated with the germination in situ induced seed germination in vitro. Seedlings which developed with these isolates in vitro were transferre d to ex vitro conditions. New leaves developed and elongated as seedli ngs continued to grow for 3 months. The seed burial method enabled the clarification of the differences in orchid-fungal specificity in situ and in vitro. We concluded that the specificity between S. sinensis v ar. amoena and fungi in situ conditions was different to that ill vitr o.