Flowering phenology, flower sterility and pollen germination in olive cultivars

Abstract

Olive (Olea europaea L.) orchard productivity largely depends on the choice of planted cultivars and their reproductive traits. Simultaneous flowering periods enable cross-pollination and high fruit set in different cultivars. Olive tree is producing both perfect (hermaphrodite) and staminate (male) flowers. Excessive production of male flowers can result in decreased yields resulting from their inability to set fruit. Low ability of pollen to germinate can also impair the productivity. In this study, the reproductive traits were analysed in twelve olive cultivars (‘Carolea’, ‘Cucco’, ‘Frantoio’, ‘Istarska bjelica’, ‘Itrana’, ‘Lastovka’, ‘Leccino’, ‘Levantinka’, ‘Maurino’, ‘Oblica’, ‘Pendolino’ and ‘Rosciola’). The earlier start of flowering was recorded for all cultivars in 2014, while the start date was delayed for nine days in 2015. Simultaneous flowering and full bloom periods were recorded for most cultivars ; however significant discrepancy also appeared for both traits. The highest proportions of staminate flowers were found for ‘Oblica’ and ‘Cucco’ and the lowest for ‘Frantoio’ in both years. Significant differences were found also in the extent of pollen germination between the various cultivars. Pollen germination varied from 3.7% (‘Lastovka’ in 2015) to 30.5% (‘Cucco’ in 2014), and the higher percentages were recorded for ‘Carolea’, ‘Cucco’, ‘Istarska bjelica’, ‘Itrana’, and ‘Oblica’. 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. Differences in environmental conditions over two flowering seasons affected the flowering timing.