Floral biology and pollen grain presentation in "Arbequina" olive (Olea europaea L.) cultivar under non-traditional crop climatic conditions

Olea europaea L. (Oleaceae), a traditional oil crop of Mediterranean basin, has been expanded considerably in the last decades to other regions of the world. "Arbequina" is one of the most widely planted cultivars due to its good agronomic and technological attributes, but interannual variability in thermal and rainfall regimes affects its regular fruit production in countries of the Southern Hemisphere, including Uruguay. To better understand the floral mechanisms that regulate fruit set in Southern Hemisphere climatic conditions, our work addresses the "Arbequina" flower functionality and pollen grains presentation along flower life span. In this andromonoecious species, the fruitful perfect flower morphs were evaluated by means of determining functional parameters such as stigmatic receptivity and pollen grain viability in each floral phenological stage, and pollen grain adhesion and pollen tube growth rate in hand pollination treatments. This flower morph did not show functional limitations under Uruguayan climatic conditions for the year in which the study was carried out, but a breeding system expressed by two different functional phases was detected. The first pistillate functional phase, where the stigma is receptive but no pollen release occurs, tends to avoid self-pollination and promotes crosspollination in the same flower. Then, a second perfectly functional phase follows, where the stigma remains receptive and the anthers release their pollen grains. In a self-incompatible olive cultivar such as "Arbequina", this pollen grain presentation further stresses the importance of combining inter-compatible olive cultivars with synchronized flowering in orchard design, as a first step to ensure fruit set.