The effects of benzyladenine and meta-Topolin on in vitro sprouting and regrowth after encapsulation of C35 citrange [Citrus sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf] microcuttings

C35, a hybrid of 'Ruby Blood' sweet orange and trifoliate orange, is a promising Citrus rootstock, mainly due to its resistance to Citrus tristeza virus (CTV), one of the most serious diseases affecting citriculture. The use of resistant rootstocks, such as citranges, is an efficient tool to fight this plant disease. This implies a continuous increasing demand of resistant rootstocks, in order to carry out the turnover of sour orange, still the most used citrus rootstock in Italy. Micropropagation can provide innovative solutions to obtain, in short time and small space, a number of plants higher than traditional propagation. Micropropagation efficiency is influenced by the culture medium composition, and in particular by the type and concentration of cytokinins. In this study, the addition of meta-Topolin (mT) and 6-benzyladenine to the culture medium at different concentrations (1.0, 5.0 and 10.0 mg L-1) was evaluated, observing the percentage of sprouting and the shoot elongation of in vitro cultured C35 microcuttings. The lowest concentration of mT resulted in the highest sprouting percentage of microcuttings after 45 days of culture. Therefore, mT was tested as a component of the artificial endosperm, in order to improve the in vitro performance of C35 encapsulated microcuttings. However, results obtained in this study were not satisfactory, being lower than the ones reported in our previous researches. Further studies are needed in order to increase the sprouting and rooting response of C35 microcuttings, particularly when encapsulated (synthetic seed conversion). Only in this way, encapsulation technology can be used as a practical tool in nursery industry.