Seed germination and seedling growth promoted by a Ceratobasidiaceae clone in Vanda thwaitesii Hook. f., an endangered orchid species endemic to South Western Ghats, India and Sri Lanka

The presence of appropriate fungal mycobiont for seedling recruitment and plant nutritional support is essential for the long-term survival of orchids in managed or restored habitats. Vanda thwaitesii Hook. f., an epiphytic orchid endemic to the Western Ghats in India and Sri Lanka, endangered due to habitat destruction, necessitates a restoration programme in order to conserve them in the native habitats. Understanding of mycorrhizal association is important for restoration and therefore a symbiotic fungus from natural seedlings of V. thwaitesii was isolated and symbiotic activity evaluated. The isolated fungus having symbiotic activity designated as 'VT3' is a slow growing species with cottony growth, binucleate and barrel shaped monilioid cells; typical characters of a Ceratorrhiza sp., anamorph of Ceratobasidium sp. Molecular identification through sequencing the internal transcribed spacer (ITS) regions of the ribosomal RNA gene revealed that it possesses 92% similarity with an uncultured Ceratobasidiaceae clone. V. thwaitesii seeds showed higher germination rate when inoculated with VT3. Majority of the control seeds failed to develop further after the initiation of germination. After the entry of fungus, the seed showed germination and 81% of the germinated seeds was transformed into protocorms in 30 days. Promeristem formation, first leaf development or second leaf initiation occurred in 95% of the protocorms in 60 days. The protocorms in symbiotic culture developed their second leaf (55%) and roots (19%) and only 24% remained at one leaf stage by 90 days. In 150 days, 43% of the seedlings obtained were with 2-3 leaves and 2 roots and 50% of the seedlings with 3-4 leaves and 2-3 roots. Asymbiotic seedlings co-cultured with the symbiotic fungus showed vigorous growth due to active colonization in their root cortex. The results suggest that the symbiotic fungus Ceratobasidiaceae clone VT3 isolated from V. thwaitesii seedlings is promising enough to continue efforts on restoration procedures for this endangered orchid species endemic to Southern Western Ghats region in India and Sri Lanka.