Efficient in vitro shoot proliferation of ‘Marrone’ accessions (Castanea sativa Mill.)

In vitro propagation of European chestnut is hampered by several issues. The highly morphogenic tissues of zygotic origin are unsuitable for cloning selected cultivars. Indeed, genotype conservation restricts the explant choice to the buds collected from adult plants, which release a heavy tannic exudation, drastically dropping the efficiency of the initial phases of culture. Even once established in vitro, ‘Marrone di Marradi’ and ‘Marrone di Zocca’ shoot cultures show tannin leakage, poor reactivity and low proliferation rates on substrates so far reported as suitable for chestnut micropropagation. Notably, chlorosis, hyperhydricity, tissue browning, early senescence, and tip necrosis of the leader shoots prevent the yield of material suitable for the subsequent steps of either rooting or grafting. In this study, both cultivars ‘Marrone di Zocca’ and ‘Marrone di Marradi’ were proliferated on substrates with several salt and hormone compositions, either previously published or newly tested on chestnut: among the latter, an alternative medium allowed a great improvement of both shoot proliferation and elongation. A consistent yield was obtained of large shoots, whose rooting ability or grafting compatibility with ‘Marrone’ seedlings are currently under evaluation.