Comparison of Growth and Flowering Traits in Cypripedium macranthos var. rebunense Germinated With or Without Symbiotic Fungi

Cypripedium macranthos var. rebunense is an endangered wild orchid in Japan. We have developed two kinds of propagation method for this orchid: an aseptic culture method through protocorm-like bodies (PLBs), and a fungi-utilizing culture method using a symbiotic fungus. Plants propagated using the two methods have been grown in our botanic garden, and now nearly 100 plants bloom every year. Using these propagated C. macranthos var. rebunense plants, we examined the differences in growth and flowering traits between aseptically- and symbiotically-cultured plants. Symbiotically-cultured plants grew vigorously and produced more flowers than aseptically-cultured plants. The survival rate at six years after potting was 94% for symbiotically-cultured plants, while that of aseptically-cultured plants was 42%. Flowering occurred depending on the plant size and not on the plant age: plants which were heavier than 10 g in fresh weight and developed 3-4 leaves at more than 10 cm were able to produce flower buds. Consequently, we propagated seedlings by symbiotic culture using fruits obtained from the cultured plants. Thus, a sustainable cultivation system for this endangered orchid, which is completely independent of plants in their natural habitat, was successfully established.