Improving in vitro mass proliferation of carob (Ceratonia siliqua L.) from seedling apices by temporary immersion systems

The carob tree (Ceratonia siliqua L.) has a high hardiness and adaptability to the climatic conditions of the Mediterranean basin, where it is cultivated but also wild genotypes are widespread. These characteristics, together with the economic value of its products (used in food, chemicals, cosmetics, processing, etc.) make this species suitable to exploit marginal and sub-marginal dry areas of the Mediterranean basin. At present, however, the large-scale cultivation of the carob tree is limited by the traditional methods of propagation that fail to meet the growing demand for bio-agronomic plants with valuable characteristics. Micropropagation is currently considered one of the most effective techniques for the massive multiplication of plants. In vitro propagation of carob, despite being studied by different researchers, still shows some difficulties that do not permit the inclusion of this technique on a market scale. For this reason, a research was carried out to evaluate the effects on shoot proliferation of a solidified and a liquid medium maintained in a temporary immersion system (Plantform bioreactor). Seedling apices were used to begin the culture. Due to the lowest incidence of contamination and browning, seedling apices present an easier adaptation to in vitro culture and therefore higher rates of in vitro initialization as compared to explants from adult trees. Liquid in vitro culture on a temporary immersion system, as compared to the one carried out on a solid medium (gellan gum), improved the efficiency of in vitro culture giving more shoots with greater height, fresh and dry weight. Thus, these first results seem to indicate that this procedure may be particularly effective in carob to obtain a more uniform mass propagation of rootstocks once the protocol will be completed. However, in these systems, particular attention must be devoted to the prevention of bacterial contamination.