Abnormalities in the ovule development of the European plum cultivar ‘Pozna Plava’ in the days following anthesis

•Degeneration of developing embryo sac in open pollinated flowers occured whithin 10 days after anthesis.•In unpollinated flowers, degeneration of developing embryo sac occured in the first days after anthesis.•High degree of viability of the primary ovules was observed after staining with aniline-blue.•Degeneration of nucellus cells was the most frequent abnormality in the secondary ovules.•The observed abnormalities do not explain the low fruit set of this cultivar.