Influence of temperature and rainfall on timing of olive (Olea europaea) flowering in southern Italy

This study concerns the flowering of the olive (Olea europaea) in a large southern Italian area. It was carried out using the "volumetric" method of pollen sampling and the analysis of the meteorological parameters of temperature and rainfall. The results show that flowering occurs mainly in May, with the maximum values in the second half of the month. Meteorological analysis showed that the biological cycle of the olive was greatly influenced by the temperature. The relationship between an increase of temperature before the beginning of flowering and the advance of flowering was 2.5 days/degrees C. Another important result concerns the value of the mean temperature which by the beginning of flowering was 16 degrees C at all monitoring stations, even if the growing degree day (GDD) requirements were different. The temperature accumulation evidenced the homogeneity of plant behaviour in dependence of latitude, except for the province of Taranto. Also, our study showed that rainfall determined a considerable decline of pollen concentration in the atmosphere, until the maximum of 80% when the value of 8 mm of rainfall/day was reached.