Formation of endomycorrhizas by an achlorophyllous orchid,Erythrorchis ochobiensis, andAuricularia polytricha

To test the mycorrhizal function of heterobasidiomycetous fungi on achlorophyllous orchids and to examine the symbiotic fungal range of a myco-heterotrophic orchid,Erythrorchis ochobiensis, synthetic cultures of the orchid seed were carried out withAuricularia polytricha isolates from Japan and Mexico. After three and a half mo of incubation, 57.0–70.7% of seeds germinated but none of them showed further growth. When cultured on peat moss at 25°C, the germination rate was 8.7% in the presence of Mexican isolate and 18.0% in the presence of Japanese isolate. Some germinated seeds developed into protocorms, and several seeds incubated with the Mexican isolate developed into plantlets after 5 mo. Pelotons were observed in the cells of protocorms and roots. The results indicated that some heterobasidiomycetous fungi could form endomycorrhizas with a myco-heterotrophic orchid. The results also showed that the symbiont ofE. ochobiensis extends, at least experimentally, to Heterobasidiomycetes. The variances of germination rate and seedling growth were suggested to be affected by the difference of isolates and culture conditions.