Flowering

Budburst marks the start of flower development. Unlike most deciduous fruit trees, where budburst coincides with the onset of flowering, in olive trees, there is a gap of several months between budburst and flowering. Flowering is fundamental to determining the yield of the olive crop. Both genetic and environmental factors influence the timing and quality of flowering. Pollination, the transfer of pollen between flowers, takes place during the flowering phase. In general, olive trees are considered allogamous and exhibit autoincompatibility. This means that pollen from different cultivars is required to fertilise the ovaries of the flowers. Although there is a large overlap in the flowering time for most of the cultivars in the Mediterranean climate, differences in flowering phenology between cultivars (Table 1) should be considered for plantations in areas outside of the Mediterranean basin and/or without nearby olive trees. It has been reported that each year there is a 22-day gap in flowering between the first and last cultivar (Figure 4). Therefore, it is essential to combine different cultivars to facilitate cross-pollination. Environmental factors, particularly temperature, have a significant impact on phenology, resulting in a variation of almost one month between the earliest and latest years (Figure 4). High temperatures accelerate and shorten the flowering period, while cooler temperatures delay and prolong it. In addition, adverse weather conditions, such as extreme temperatures or high humidity, can disrupt the pollination process and result in significantly reduced fruit set. 

Table 1: Classification of chilling requirements, flowering  and date of budburst in the World Olive Germplasm Bank of Córdoba (Spain) and Marrakech (Morocco).

Figure 4: Evolution of timing of flowering for a group of 124 cultivars over 12 different years in the World Olive Germplasm Bank of Córdoba, Spain (in Barranco and Rallo, 2005).

Percentage of cultivars