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

Abstract Factors such as the stage of ovule maturity and longevity at flowering, when the stigma is able to receive the pollen, are significant in terms of fruit set. Various abnormalities during ovule development can often limit pollination, effective pollination period (EPP) and fruit set. In the plum cultivar ‘Pozna Plava’ ( Prunus domestica L.), in the ovaries of open-pollinated flowers and of emasculated unpollinated flowers, we investigated abnormalities in the tissues of primary and secondary ovules during the time of anthesis until 10 days thereafter. At the same time, the viability of the ovules of the unpollinated flowers was examined. Abnormal ovules were considered those with degenerations in the egg apparatus, inverse arrangement of egg cells, more than eight nuclei in the embryo sac as well as degeneration of the nucellus and integuments. In primary ovules, the most frequent abnormality in open-pollinated and unpollinated flowers was the degeneration of the egg apparatus, with frequencies of 14.3–50.0% and 10.0–89.0%, respectively. In the secondary ovules, in both treatments, a completely different picture was obtained. The processes that led to abnormalities in the structure of the secondary ovules first occurred in the cells of the nucellus, while the elements of the embryo sac had a relatively normal cytological organisation. However, the observed abnormalities do not explain the low fruit set of this cultivar.