In the olive Olea europaea (L.), the polyamides (PAs), putrescine, spermidine, and spermine, when added exogenously at a concentration of 1 mm in the in vitro rooting medium, combined with 5 μm auxin concentration, promoted early rooting and increased the final rooting percentage and the number of roots per explant. The effect was less evident in olive explants rooted with the basal blanching method; thin-layer chromatography of total endogenous PAs in `these explants revealed lower levels on day 2 compared with controls, while by day 5 PA concentrations in both had fallen to similar levels. Furthermore, putrescine decreased the pH of the medium by 0.5 units around the explants. PAs had little effect on apple Malus pumila (Mill.) and no effect on almond Prunus dulcis (Miller) D.A. Webb and pistachio Pistacia vera (L.). There were also some positive effects observed, but only in olive, when rooting was induced by Agrobacterium rhizogenes in auxin-free medium. Few plantlets showed agropine-positive roots.
Loretta Bacchetta, Maria Aramini, Claudia Bernardini and Eddo Rugini
The hazelnut (Corylus avellana) is one of the most important crops in the Mediterranean basin. The availability of efficient and reliable in vitro propagation could valorize the local genetic resources. Different studies have been carried out for the definition of an efficient hazelnut micropropagation protocol. These have usually been performed on the most important cultivars, but the application of the micropropagation protocol to the minor ones has produced contradictory results and the technique sometimes had less success than the traditional one. The aim of this work was to gather knowledge and additional information on the in vitro performance of some minor cultivars in comparison with the most used for micropropagation. A revised procedure for the specific medium formulation is suggested. The sterilization and culture establishment phases are discussed in detail. The role of zeatin and 6-benzylamminopurine (BA) in shoot proliferation in the Italian traditional cultivars is compared to improve this phase. The rooting stage proves to be one of the most crucial steps in achieving a large-scale commercial application of hazelnut micropropagation.
Cristian Silvestri, Gianmarco Sabbatini, Federico Marangelli, Eddo Rugini and Valerio Cristofori
An accurate protocol for the in vitro propagation of a commercial wolfberry (Lycium barbarum L.) cv. Nixia 1 has been developed through axillary shoot proliferation. Driver and Kuniyuki Walnut (DKW) medium supplemented with 6-benzylaminopurine (BAP; 0.5 mg/L) and sucrose 3% w/v gave the best results compared with other basal media tested, with significantly improved production of multiple shoots direct from nodal segment explants, resulting in an average of 6.73 shoots/explant with an average of 7.45 nodes/shoot that would potentially form new explants. Rooting of shoot explants was carried out both in vitro and ex vitro with 0.5 and 1 mg/L of indole-3-butyric acid (IBA), with or without adding putrescine (160 mg/L). In all cases, rooting efficiency resulted very high, and putrescine was effective only when combined with a low concentration of auxin. Plantlets were hardened off in jiffy pots under greenhouse conditions, with a survival rate of more than 90%. Ex vitro rooting, performed by dipping in an aqueous solution of IBA 100 mg/L, is the preferred technique not only because rooting and acclimatization are very high but also reducing micropropagation to one phase is more economical.
Eddo Rugini, Cristian Silvestri, Marilena Ceccarelli, Rosario Muleo and Valerio Cristofori
In Olea europaea L. subsp. europaea, tetraploid genotypes do not exist in nature. Herein, we report the first example of selection of tetraploid olive plants, obtained by combining physical mutagenesis and biotechnology techniques. Stable tetraploid (4n) and diploid (2n) genotypes were isolated in vitro through shoot-tip fragmentation of two mixoploid mutants derived from the gamma irradiation of self-incompatible Leccino and self-compatible Frantoio cultivars. In this study, the stable mutants FRM5-4n, FRM5-2n, LM3-4n, and LM3-2n were characterized in the field for vegetative and reproductive behavior with the aim to use them as varieties or dwarfing rootstocks. The stable 4n genotype of Leccino acquired self-fertility whereas the 4n Frantoio maintained it. A high and constant yield was showed by LM3-2n during 9 years of observation, maintaining the same oil quality as the Leccino wild type (wt). Moreover, the LM3-2n acquired the capacity to be intercompatible with the diploid mutant Leccino dwarf (LD) and with the Leccino wt. This acquired property would allow for a reduction of heterozygosity in the offspring, if crossed with each other for some generations and with the Leccino wt, because it is a sort of self-fertilization. When used as rootstocks, both 4n and 2n Leccino mutants proved to be very effective for reducing the scion size of the high-vigor Canino cultivar, which is well known for its excellent extravirgin oil. Finally, it was demonstrated that the self-grafting of vigorous cultivar caused a reduction in plant size, thus suggesting that it is possible to produce semidwarf plants from vigorous genotypes to consider them in high-density olive orchards.