Preliminary approach to mycorrhization of micropropagated linden sprouts with Tuber borchii

Linden is a host plant particularly interesting given that in nature it forms ectomycorrhizas with all Tuber species of economic value. The propagation of the linden results to be quite problematic and according to Magherini and Nin especially the production of seed material because the seed germinates with great difficulty both for the incapacity to obtain viable seed and for the leathery integument. In the genus Tilia there is a strong dormancy, especially the physiological dormancy is dominant and, to overcome it, the intervention of hormones is necessary. Consequently, in the truffle nursery market it is difficult to have mycorrhized linden trees available, indeed, also because of the high incidence of costs for propagation. In our opinion, a possible solution may be the possibility of propagating Tilia in-vitro and achieve mycorrhization still in partial asepsis conditions. In vitro plant propagation techniques allow the regeneration of different forms of propagules, such as somatic embryos (bipolar organs) or adventitious sprouts (unipolar organs). Therefore, it is very interesting the possibility of establishing a mutual symbiosis between fungus and plant already during the aseptic condition, which is realized after the rooting phase, in order to allow the seedlings to overcome the first phases of the ex-vitro acclimatation, always delicate and dangerous situation, thanks to the interaction with the symbiont fungus. The aim of the work is to obtain vitro-derived plantlets with root system on which, in the next phase, make a sporal inoculum of Tuber borchii Vittad. (bianchetto or marzuolo) thus obtaining mycorrhized linden plants. For this reason, it has been identified an effective micropropagation protocol, which allowed to proliferate in vitro and to root in mixed vitro-vivo in conditions sprouts of Tilia platyphillos Scop. which will be mycorrhized later with inoculum of T. borchii. Initial plant material, as uninodal portions, equipped with buds and without leaves, was excised from shoots of the year; then they have been subjected to decontamination, in order to obtain sterile explants and ready to be grown. The completely decontaminated explants were launched to the multiplication phase, subjected to the effect of a different nutritional component, which could stimulate the vegetative activity. The shoots that have reached a size considered suitable for the next steps of the experiment have been used for the subsequent rooting phase on soil. The rooting method on soil is now a widespread system and is defined as "mixed vitrovivo system". The main advantage is to obtain roots that are structurally much more similar to the definitive and partially functional root systems. Therefore, the rhizogenesis in Tilia was induced by IBA and the results showed all its efficiency as an auxin suitable to stimulate rootin. The inductive treatment with IBA powdered has allowed to obtain 58% of the rooted shoots, while in the remaining 42% of the cases, the characteristic enlargement of the part of tissue treated with auxin has been recorded. The rooted shoots have developed an average of 2.1 roots/shoot with an average length of 16.6 mm. Finally, after only 4 months from the inoculum, up to 80% of mycorrhization with T. borchii was observed by morphological analysis and after 6 months the average of mycorrhization was 45%. These results, although still preliminar, are very interesting and promising in order to obtain micropropagated and mycorrhized lindens with T. borchii