Photoautotrophic Micropropagation Systems (PMS)

Using unconventional supporting systems to increase survival rates of micropropagated plantlets of threatened species

Photoautotrophically grown Myoporum mauritianum, a threatened Mauritian endemic species
Photo: Viswambharan Sarasan

Endemic taxa from global biodiversity hotspots and small islands are unique and they are amongst the most threatened group of plants globally. Climate change, invasive alien species and limited resources available in host countries are among several factors that contribute to the plight of these species. Conservation of these plants is a top priority for international and national conservation agencies. As part of the recovery and restoration of selected species from these areas in vitro propagation is preferred over conventional systems due to the limited amount and recalcitrant nature of available plant material. Very limited material is available for collection in many cases and the problem is exacerbated by the fact that rooting and transplantation can be problematic. Agar is widely used as the supporting mediumin all stages of in vitro propagation, from culture induction to rooting. The roots produced in agar may not be of good quality and this may result in poor transplantation and can directly contribute to failure in reintroduction/restoration initiatives. After transplantation of propagules of woody species, raised in culture on an agar-based medium, wilting is widely reported.

A healthy root system is essential for the development of a robust shoot system as they are complementary to each other. Poor ventilation can lead to the development of plants with poor anatomical features that could reduce the plant’s ability to acclimatise. This is due to the reduction or absence of epicuticular and cuticular wax, reduction in length of epidermal hairs and permanently open non-functional stomata which do not respond normally by closing in the dark or under conditions of lower relative humidity. This results in a high rate of transpiration of the plants upon transplantation and eventually results in a low survival rate. The use of large culture vessels and unconventional supporting systems in vitro for the rooting/weaning stages has been found to be useful for threatened plants. Ferns, woody shrubs and trees, and species mass propagated for restoration programmes are being studied for improving transplantation success of the propagules.

The case study conducted in the jelly fish tree (Medusagyne oppositifolia) from Seychelles showed that unconventional supporting materials and use of pre-weaning stages can improve the quality of the propagules during rooting and prepare plantlets for successful weaning later on. This has also been successfully applied to the transplantation of critically endangered Ascension Island ferns including Pteris adscensionis and Anogramma ascensionis.