Ovule senescence in the ovary of the Balkan region's autochthonous sweet cherry genotypes

Diversity in sweet cherry (Prunus avium L.) is a source of adaptation to environmental conditions. Genotypes harbouring trait tolerance to stress are interesting sources for potential temperature-tolerance genes. Higher flowering temperature accelerates ovule senescence, which leads to female gametophyte degeneration and ovule abortion. This study was carried out to investigate the ovule senescence of sweet cherry landraces of Balkan origin ('Ohridska Crna' and 'Dolga Šiška') under the prevailing Mediterranean climate of Ohrid Lake vicinity (Republic of North Macedonia). Monitoring was undertaken using fluorescence microscopy on emasculated pollinated flowers (cross-pollination) and non-emasculated open-pollinated flowers (open pollination), at three different stages of pistil fixation (3^rd, 6^th and 10^th day from the full flowering date). The results showed that the appearance of ovule fluorescence, as an indicator of its senescence, was more pronounced in the ovaries of 'Dolga Šiška', as compared to 'Ohridska Crna'. Investigation of ovule senescence and fruit set pointed to the complex dependence on the pistil genotype and pollination variant, as well as flowering temperature, which together contribute to the main factors' interaction. The research also revealed that, in sweet cherry, primary ovule fluorescence on the 6^th day after full flowering strongly correlated negatively to fruit set.