Microsporogenesis and meiotic abnormalities in different ‘Oblačinska’ sour cherry (Prunus cerasus L.) clones

• We studied key aspect of microsporogenesis in Oblacinska sour cherry (Prunus cerasus L.) clones.
• Significant differences were observed within the clones and among the years of study.
• Abnormal conjugation, chromosomes lagging and irregular number of microspores at ‘tetrads‘ stage was the most prominent anomalies.
• Due to cytomixis, syncyties made of 2 and more cells were built.
• In some syncites genome maintained its integrity, while in some complete genome fusion was recorded.
• Abnormalities during meiosis influenced the reduced in vitro pollen germination and low pollen tube length in some clones.

The Oblačinska sour cherry (Prunus cerasus) is a mixture of different clones with similar tree and fruit characteristics that is indigenous to and widely planted in commercial orchards in Serbia. Sour cherry, including Oblačinska sour cherry clones, exhibits irregular meiosis which may contribute to low fruit set in some selections. The goal of this study was to examine the process of microsporogenesis and to determine if meiosis and its anomalies effect the in vitro pollen germination and pollen tube length in four ‘Oblačinska’ sour cherry clones that differ in fruit set and yields. All clones displayed varying degrees of chromosomal abnormalities in all meiosis sub-phases. The abnormalities became evident from late pachytene with more than half of the pollen mother cells (PMC) showing abnormal conjugation of chromosomes in metaphase I. The lowest number of PMCs with laggards was in clone III/9 and the highest in clone XIII/1. In second division, the univalent and multivalent association was observed at metaphase-II, the lagging and stickiness in anaphase-II, and the phenomenon persisted up to the microspore stage. In all four ‘Oblačinska’ clones, PMCs exhibited cytomixis phenomena, however, it was only observed in the second experimental year. Cytomixis differed among the four clones but was equally frequent in all stages of meiosis. The syncytia formed, most often consisted of 2–3 PMCs that were at the same phase of meiosis, and exhibited common cytoplasm and occasionally nuclear fusion. In vitro pollen germination and pollen tube length significantly differed between the clones. Most probably abnormalities during meiosis, regardless of the good results of pollen germination, influenced the reduced potential clones XI/3 and XIII/1.