Novel micropropagation and weaning methods for the integrated conservation of a critically endangered tree species, Medusagyne oppositifolia

Medusagyne oppositifolia is a critically endangered monotypic species with only a few trees left in the wild. Due to invasion and habitat clearance, genetic diversity of this species has been reduced to an alarmingly low level. Long-term in vitro cultures of M. oppositifolia were slow-growing and eventually lost the ability to multiply and root. Because of the lack of new seed and vegetative materials, efforts were made to rejuvenate the existing cultures. This was attempted by a series of steps involving serial pruning of the shoot tips and growing on a modified MS medium containing silver nitrate and thidiazuron. Rapid cycling clonal propagules were produced this way from cultured nodes. Isolated shoots were rooted on Florialite?, and rooted plants were weaned in a transition stage using a Nutrient Film Technique (NFT) hydroponic system before being completely weaned under glasshouse conditions. The importance of screening cultures for multiplication and rooting efficiency during long-term maintenance is discussed in the context of stress metabolite production and its influence on growth in culture. Factors contributing to rejuvenation of old cultures, application of unconventional supporting systems for rooting and application of the hydroponic system as a weaning tool are also discussed.