Abstract:

Aims The degree of specificity of mycorrhizal association in tropical orchids has been controversial for many years. Our objective is to address this issue.
Methods Twenty-two endophyte fungal strains isolated from the roots of wild temperate terrestrial orchids were inoculated with the seeds, protocorms and seedlings of tropical epiphytic orchid species Doritis pulcherrima in flasks. Transverse sections of roots were observed by microscope.
Important findings After 20-weeks cultivation, only the fungal strains Cf1 and Mm1 caused swelling of the embryo, and nine caused differentiation of the protocorms into leaves or roots. The other fungal strains were pathogenic or had no function in seed germination and protocorm differentiation. In the seedling-fungi symbiotic treatment, the survival rate of the seedlings reached 100% and 11 of 22 fungal strains significantly enhanced the seedling growth. The fungal strain Mm1 had the most significant effect on increasing fresh mass of seedling. The existence of pelotons in the cortex of the roots of the protocorms and seedlings indicated successful infection. The effects of 22 endophyte fungal strains on seed germination, protocorm development and seedling growth of D. pulcherrima showed that the endophyte fungi did not enhance seed germination but were associated with the protocorms and seedlings; However, no one fungus was associated with all three key stages simultaneously. Our study suggested that the degree of specificity of tropical epiphyte orchids is influenced by the development stages of the plant.

Key words: epiphytic orchid, mycorrhizal, specificity, symbiotic germination in vitro, symbiotic cultivation, survival strategy