Relationships between yield and pollen concentrations in Chilean hazelnut orchards

Chilean hazelnut (Corylus avellana L.) industry has been recently experiencing a solid development and nut production is consistently increasing. Corylus avellana is subjected to strong inter-annual yield fluctuations, which raise the issue of price predictability. In alternate bearing, a high fruit load hinders flower initiation thus leading to a smaller fruits production in the following year. This suggests the use of pollen airborne concentration as a proxy for flowers number to predict hazelnut irregular bearing. We addressed this question using high-resolution yield and pollen data collected on four hazelnut plantations located in Central Chile, and three hazelnut cultivars. Pollen parameters were calculated from modelled and non-modelled pollen seasons, after selecting the best modelling approach. An alternate bearing index was calculated to characterize hazelnut biennial bearing and to select plots with high yield variability. The calculated pollen parameters were then correlated with yield data. Significant correlations were found between pollen parameters and nut yields, with stronger relationship when alternate bearing was higher. The modelled peak of the pollen season presented the highest variability (average CV = 81 %) and its positive correlation with crop production (ρ = 0.45) was consistent across sites and cultivars. Our results support the integration of airborne pollen data in hazelnut yield prediction systems, as predictors of alternate bearing and to forecast annual yield.