Flower sterility and the germination ability of pollen as genetic traits of seven olive (Olea europaea L.) cultivars grown in Croatia

Abstract

SummaryTo evaluate and use olive (Olea europaea L.) cultivars appropriately, studies on their reproductive biology are necessary. The proportion of staminate flowers and the success of pollen germination in olive were found to vary depending on cultivar, climatic conditions, and the site of cultivation. In this study, floral gender and pollen germination were analysed to assess the reproductive potential of seven olive cultivars in Croatia. The percentages of staminate flowers and pollen germination in four Croatian (‘Drobnica’, ‘Lastovka’, ‘Levantinka’, and ‘Oblica’) and three Italian (‘Itrana’, ‘Leccino’, and ‘Pendolino’) olive cultivars were determined over six flowering seasons in three orchards. We observed variable numbers of flowers per inflorescence in the different cultivars. The proportion of staminate flowers ranged from 2.6% (‘Leccino’ in 2006) to 66.0% (‘Oblica’, 2009), and fluctuated with cultivar, year, and orchard. ‘Leccino’ and ‘Pendolino’ developed lower percentages of staminate flowers than ‘Lastovka’, ‘Levantinka’, and ‘Oblica’ in most experimental years. Higher fruit set was observed for cultivars with lower percentages of staminate flowers, indicating that olive tree productivity depends on the number of fully developed flowers. We found significant differences in the extent of pollen germination between the various cultivars, orchards, and germination media used. Pollen germination varied from 2.1% (‘Lastovka’ in 2006) to 31.6% (‘Oblica’ in 2005). ‘Oblica’ and ‘Levantinka’ showed significantly higher percentages of pollen germination than ‘Leccino’ and ‘Pendolino’. There was no difference in the order of cultivars analysed according to their proportions of staminate flowers and the success of pollen germination between the orchards at Mravince and Kastela. Our results suggest that the level of pistil abortion, and the success of pollen germination, are genetically determined and are most likely an evolutionary adaptation to redistribute available resources.