Development of a New Micropropagation Protocol and Transfer of In Vitro Plants to In Vivo Conditions for Cascade Hop

The vegetative propagation of hops, despite being a reliable method, is not very common due to the unavailability of the plant material. In this study, the technique of in vitro propagation was applied to the Cascade variety of Humulus lupulus L. The plant material was collected from a private field in Sicily; the explants were subjected to sterilization before in vitro culture. Single-node explants were placed in in vitro culture in nine different culture media for multiplication. Thidiazuron (TDZ), Benzyladenine (BAP) and meta-Topoline (mT) were tested for multiplication phase. For the rooting phase, five types of different culture media were evaluated. Binodal cuttings coming from the previous multiplication test were placed in the culture. The rooting media differ from each other in the concentration and ratio of two auxin hormones: Indolo-3-acetic acid (IAA) and Indole-3-butyric acid (IBA). In vitro rooted plants obtained from the rooting phase were transferred to ex vitro conditions in a microbox with agri-perlite and a solution containing Murashige and Skoog (MS) basal medium at half concentration. With a culture medium containing the highest TDZ doses (H6) and combination with cytokinin (H8 and H9), the highest shoot percentage was obtained. After 3 months of in vitro culture, the highest shoot percentage was observed in the culture medium with 2 mL L^-1 of BAP. The highest rooting percentage, roots numbers and root length were found when the culture medium was supplemented with 1 mL L^-1 of IAA. The usage of agri-perlite and MS at half concentration, without PGR, allowed us to obtain a 99.1% survival rate. This micropropagation protocol is useful for obtaining virus-free plants and for the development of the brewery industry.