Ovule Longevity Determines the Fruit Set and Effective Pollination Period in Sweet Cherry Cultivars Under Mediterranean Climate Conditions

The effective pollination period (EPP) is a key factor determining fruit set in sweet cherry, as it depends on the overlap between pollen tube growth and ovule longevity. This study investigated the duration and components of the EPP in three autochthonous cultivars (‘Stonska’, ‘Gomilička’, and ‘Tugarka’) grown in the Mediterranean region of Croatia over two consecutive flowering seasons. The EPP was determined under field conditions using sequential hand pollinations, while stigma receptivity, pollen tube growth, and ovule viability were assessed by fluorescence microscopy. Significant genotypic and seasonal variation in EPP and fruit set was observed. ‘Stonska’ and ‘Gomilička’ exhibited extended EPPs (9 and 11 days) and moderate to high fruit set. In contrast, ‘Tugarka’ showed a considerably shorter EPP (4–5 days) and consistently low fruit set (