Orchid Mycorrhizae: The Forgotten Biological World

Orchids are a treasured resource and valuable wealth for botanists, floriculturists, ethonobotanists, ecologists and evolutionary biologists. They are also valued by the product of perfect plant-fungi and plant-animal symbiosis/mutualisms. The medicinal value and possible orchid flower export for the sub-continent are not yet adequately explored and estimated. In Andhra Pradesh there are 76 orchids reported. More than half are epiphytes while majority are geophytes. Around 18500 species and 1.5 lakh hybrids are reported globally. Fungal stimulus is required for seed germination. Fungal infections lead to endotrophic and intracellular association. Pelotons are formed in the host cells. The digestion of fungus in host cells results in the utilization of nutrients by the host. The fungus gets carbohydrates from the orchid while plant gets nutrients. Mycotrophic way of life has been established in orchids. Fungi like Armillaria, Rhizoctonia, Corticium, Marasamius, Thanetophora and Glomus have been found to form symbiotic association with orchids. Recently, the growing of orchid seed with the help of culture media has revolutionized the commercial orchid production. In view of problems faced by the orchid growers, there is a need for propagation of orchids through seeds for commercial green house crops and for conservation of orchid wealth which are now at the verge of extinction. All members of the family orchidaceae are thought to form orchid mycorrhizas. The symbionts in roots of an orchid in the field are considered to be ecological symbionts of the plant. A great diversity of fungi can germinate seed in the laboratory than is found in the field. This larger group has been referred to as the physiological symbionts. It is also possible to isolate physiological symbionts from soil adjacent to functional plants in the field but they are not always inside the roots. The fungus recolonizes the plant each year and continues to benefit the host. With more than 18000 species, the orchid family is large and diverse. The fungi associated inside beneficial symbionts are also fungi of no known function. Most of the fungi associated are difficult to identify as they are in vegetative stage or belong to anamorphic fungal genera. The present paper includes data on orchid flora available from Andhra Pradesh, their endemics, and also reviews the orchid-mycorrhizal status along with author's data on orchidoid mycorrhizae.