Viability and germinability in long term storage of Corylus avellana pollen

European hazel is one of the most important fruit tree crop in the world and since the demand of nuts is growing, the cultivation area of this species has extended outside its native range. Many hazel cultivars are self-incompatible and the flowering period of male and female flowers in different cultivars only partially overlaps, so hazel requires genetically compatible pollinizer cultivars in order to obtain a good yield. For these difficulties and since the male and female flowering can vary from year to year in response to climate variability, artificial or supplementary pollination can be used to improve the final yield and optimize the cross-pollination, in particular outside the native range, where the wild type is absent. Therefore, the aim of this work is to evaluate the best temperature conditions (20, 4, − 30 °C) for a long-term storage of pollen in order to maintain a high viability level. Pollen coming from three cultivars (Tonda Gentile delle Langhe, Tonda di Giffoni and Tonda Gentile Romana) and wild hazel were collected during two winters. Several methods (in vitro pollen germination, 2,3,5-triphenyltetrazolium chloride test, fluorescein diacetate and propidium iodide solution) were used to obtain a reliable estimation of pollen viability and germinability. All methods, although highlighting differences among cultivars, demonstrated that the − 30 °C temperature storage condition is the best in order to maintain a high viability level (>40–50%) at 150 days from harvesting.