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

Abstract

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. Key MessageA micropropagation protocol was developed for the rare and endangered tree species Zelkova sicula. The in vitro procedure allowed to overcome seed sterility providing a plant stock successfully reintroduced in the wild.

From glacial refugia to hydrological microrefugia: Factors and processes driving the persistence of the climate relict tree Zelkova sicula

“…On the other hand, as suggested for Quercus species from Poland (Dzialuk et al., 2007) or Lomatia tasmanica from Tasmania (Lynch et al., 1998), triploidy most often associates with reduced fertility or even with absolute sexual sterility (Eckert, 2002). For the Sicilian relict populations, this trait is at odds with any possible natural migration toward other suitable sites (Carra et al., 2019), resulting in their definitive “entrapment” in the current isolated enclave locations.…”

Micropropagation of Endemic Endangered Taxa of the Italian Flora: Adenostyles alpina subsp. macrocephala (Asteraceae), as a Case Study

“…Plant regeneration via callus formation often gives rise to somaclonal variations [ 22 ]. Variations in plants can be analyzed by various molecular markers or can be estimated by flow cytometry (FCM) [ 23 , 24 ]. Somaclonal variations, when they do not involve a change in the chromosome number, can be useful for increasing the genetic variability of the propagation material to be used for conservation interventions [ 25 ].…”

“…In addition, micropropagation techniques can also be employed to study the ecological factors that influence plant development [ 20 , 21 ]. Collecting and maintaining endangered plants in tissue culture or cryopreservation to support the species’ survival and reduce its extinction risk can be a valuable alternative [ 22 , 23 , 24 , 25 ]. However, these solutions are only feasible if the practitioner can restore a rooted plant from tissue culture or cryopreservation that is then capable of being transplanted into the wild [ 26 , 27 ]; hence, the importance of developing successful protocols arises.…”

In vitro germination and regeneration of Senna artemisioides, a valuable leguminous ornamental shrub

“…The successful acclimatisation and survival of in vitro propagated plants is essential for the establishment of a successful micropropagation protocol. Several factors could interrupt the growth and lead to decline and death (Amoo et al, 2011;Bunn et al, 2011;Carra et al, 2019). This stage is critical and the introduction of a new species in the floriculture industry as a new ornamental species is depended on the success of this.…”