Preliminary assessment of cytological characteristics of two European pear (Pyrus communis L.) cultivars

Pear (Pyrus spp.) is one of the most important pome crops in the world and Iran. Numerous pear cultivars are available and commercially cultivated in more than 50 countries in the temperate regions. European (Pyrus communis L.) and Asian (P. serotina L.) pears are two major commercial pear species in the pear collection and commercial orchards. This experiment was conducted to explore seed germination and to further study the cytology of two European pear cultivars ‘Dargazi’ and ‘Shahmiveh’, as pear rootstock in the pear orchards in Iran. Pear seeds were supplied from the commercial nursery in Mashhad, Iran. Seeds were washed, disinfected, and treated with fungicide and kept moist in a refrigerator at 4°C. Germinated seeds were transferred into Petri dishes for chromosome and cytological studies. The 0.5 cm-long root tips were pretreated with 8-hydroxyquinoline at room temperature (RT) for 6 h, followed by washing in distilled water. For the fixation process and to fix or stop the chromosomes at the desired metaphase stage of cell division, the root samples were fixed in Carnoy’s solution, including glacial acetic acid:ethanol (1:3; v/v) at 4°C for at least 24 h. For chromosomal analysis, the fixed root samples were washed in distilled water, hydrolyzed in 1 M HCl at 60°C for 30 min in a water bath, and stained in 2% (w/v) aceto-orcein at RT for 24 h in darkness. The stained root tips were thereafter squashed in a drop of 45% (v/v) acetic acid. The results showed that both European cultivars were diploids, having a chromosome number of 34. To estimate the genome size (2Cx DNA) of each cultivar, flow cytometric studies were performed, using the PI staining method and Solanum lycopersicum ‘Stupicke’ (2C DNA = 1.96 pg) as a reference standard. For this purpose, 1 cm² of fresh and fully developed leaves of either pear plants or standard plants were used. Three replicates of individual plants were used. The genome size of ‘Dargazi’ and ‘Shahmiveh’ were 1.01 and 1.25 pg, respectively.