The effects of meta-Topolin and benzyladenine on in vitro organogenesis from epicotyl cuttings of Troyer citrange (Citrus sinensis [L.] Osbeck × Poncirus trifoliata [L.]

Citrus tristeza virus (CTV), worldwide considered as one of the worst disease affecting Citrus plants, produced great changes in citriculture, mainly because it made mandatory the turnover of the sensitive sour orange rootstock with virus resistant ones. Among them, Troyer citrange has become one of the most employed rootstocks, due to its CTV tolerance and to the positive characteristics induced to the scion fruit production. Unfortunately, in Italy, there is a scarcity of seed mother plants. Micropropagation can be a solution for this problem. Among the in vitro techniques allowing the production of good quality true-to-type plants, the regeneration from seedling epicotyl cuttings generally guarantees a high proliferation rate and it is particularly suitable for citranges, because of their high level of polyembryony. A key factor to induce the regeneration from epicotyl cuttings is the addition, in the culture medium, of exogenous cytokinins, such as 6-benzyladenine (BA). To overcome some of the BA flaws, a new family of endogenous aromatic cytokinins, named meta-Topolin (6-[3-hydroxylbenzylamino] purine, mT), has recently started to be used. In this research, the influence of mT and BA on organogenesis from Troyer citrange epicotyl cuttings was evaluated. For more than three months, a good proliferation rate was observed in these explants. However, no significant differences were detected in the explant response to the different media tested. Obtained results demonstrated that mT can be a valid alternative to BA in order to induce organogenesis from epicotyl cuttings. Further studies are necessary to increase the proliferation rate, evaluating new cytokinin combinations and concentrations.