Clonal propagation and hardening of epiphytic orchids (Aerides multiflora and Rhyncostylis retusa) for sustainable conservation and utilization

Abstract

The study involves devising an efficient method for in vitro protocorm-based plant production, as well as ex vitro establishment of Aerides multiflora and Rhynchostylis retusa. Both the orchids fall prey to the unscrupulous collection from the wild as they are widely used in the traditional medicinal system. Tissue culture technology can be effectively used for mass production of both the orchid species if the planned methodology is used for transplanting the regenerated plantlets into field conditions. MS medium supplemented with natural additives proved to be most optimal for protocorm development from seed explants (giving an average of 94 % to 97 % germination) and further multiplication while Mitra medium was best suited for complete plantlet regeneration from cultured protocorms. In A. multiflora an average of 3.33 shoots and 2.67 roots per protocorm, and in R. retusa mean number of 4.33 shoots and 3.10 roots per protocorm could be obtained on Mitra medium. Tissue culture raised plantlets of both the orchids were hardened in vitro and then shifted under polyhouse conditions. Peat moss, coconut husk, bark shavings, charcoal, and brick pieces, in varying combinations, were tried for optimal growth. Based on the best plantlet survival rate, 90 % in A. multiflora and 100 % in R. retusa, the growth medium combination of peat moss with charcoal, and bark shavings was selected to be the most optimal for orchid growth when kept at a temperature of 25–30 °C, relative humidity 60–70 %, and periodic watering only to avoid drying. The standardized methodology can be utilized for the field plantation of these two important orchids as a means of conservation and propagation strategy.