Relationship among carbohydrates content, viability and germinability in pollen of European hazelnut (Corylus avellana L.) cultivars

Fertilization strictly depends on the availability of viable and germinable pollen. Pollen viability can vary depending on the cultivar and the time of the dispersal, but the physiological basis of this pattern is still poorly understood. Carbohydrates play a pivotal role in regulating the osmotic equilibrium, as well as representing the main substrate for the cellular respiration necessary for pollen maintenance and germination. Pollen grains from four Corylus avellana L. cultivars (Camponica, Tonda di Giffoni, Tonda Gentile sin. ‘Tonda Gentile delle Langhe’ e Barcelona) were analyzed to verify whether viability and germinability are related to the carbohydrate concentration (glucose, fructose, sucrose and starch) during dispersal. Samples were collected from two different hazelnut collection fields located in Piacenza and Chieri, and compared with each other. In both fields, all genotypes were characterized by the absence or very low concentrations of glucose and fructose, while starch showed stable values. Sucrose had a fluctuating trend, largely reflecting that of viability and germinability. Pollen viability was positively correlated with sucrose content, regardless of the genotype or field considered. Pollen germinability was also positively correlated with viability in some cultivars but not in all locations tested. These results suggest that viability and germinability could be good predictor parameters of the pollen suitability at different stages of the pollination and fertilization process. On the other hand, no significant correlation emerged between pollen germinability and sucrose content. The intervention of a third factor, such as the climatic variations between the two areas, could further explain the data obtained. The findings of this research confirm the role of sucrose in supporting hazelnut pollen viability.