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 pathology 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 a short time and in a small space, a number of plants higher than traditional propagation. Micropropagation efficiency is also affected 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 (BA) to the culture medium at different concentration (1.0, 5.0 and 10.0 mg/L) was evaluated, observing the percentage of sprouting and the shoot elongation of in vitro cultured C35 microcuttings. After 45 days, observed data showed that, at the lower concentration, mT provided better results than BA, regarding the in vitro response of microcuttings, inducing a higher in vitro sprouting rate. Due to these encouraging results, mT has been added to the artificial endosperm in order to increase the in vitro performances of C35 encapsulated microcuttings. Indeed, results obtained in this experiment were not satisfying, 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, and, above all, the synthetic seed conversion. Only in this way, encapsulation technology will finally be a real and practical tool for nursery activity.