Overcoming sexual sterility in conservation of endangered species: the prominent role of biotechnology in the multiplication of Zelkova sicula (Ulmaceae), a relict tree at the brink of extinction

Biotechnology provides valuable tools to support conservation of plant species, especially in case of threatened taxa or when dealing with seed unavailability, low viability or sterility. However, plant cell culture methods have often to face problems associated with tissue recalcitrance to in-vitro systems. Recalcitrance can be related to a variety of triggering factors, involving many efforts and manipulations within one or more of the micropropagation stages before obtaining successful results. An in-vitro propagation protocol was developed for Zelkova sicula, a very rare and endangered relict tree, endemic to Sicily (Southern Italy). The species revealed extremely recalcitrant to in-vitro culture approaches, but after many trials throughout a number of years an effective micropropagation protocol was completed. The rooting rate was about 84% of the treated explants, 8% of which were successfully acclimatized outdoor and reintroduced in the wild within a comprehensive conservation project. The technique allowed to overcome the problems of sexual sterility of this species, hence contributing concretely to contrast the problems connected with its conservation. However, additional efforts need to be carried out in order to refine the acclimatization step and further improve the whole process effectiveness.