Variation in genome size and stomatal traits among three Sorbus species

In this paper, ploidy in Sorbus cibagouensis H. Peng & Z. J. Yin, S. hypoglauca (Cardot) Hand.-Mazz., and S. vilmorinii C. K. Schneid was assessed by means of relative genome size using flow cytometry. At the same time, stomatal characteristics were observed by light microscopy and scanning electron microscopy. Based on flow cytometry profiles, the genome sizes of S. cibagouensis, S. hypoglauca, and S. vilmorinii were (1.480±0.039) pg, (1.513±0.041) pg, and (2.675±0.065) pg respectively. The cytotypes of S. cibagouensis (2x), S. hypoglauca (2x), and S. vilmorinii (4x) were also revealed. The stomata of the three Sorbus species did not sink and the guard cells had no ‘T’ type thickening structure. Furthermore, the stomata were distributed in the lower epidermis of the leaves and were anomocytic type. The outer stomatal rim ornamentation of S. cibagouensis and S. vilmorinii was smooth, whereas that of S. hypoglauca was short rod waxy. These results showed that there were significant differences in stomatal size among the three Sorbus species. Furthermore, genome size was positively associated with the ploidy of Sorbus, which could therefore be used for ploidy identification. Although the correlation between stomatal traits and ploidy was not significant, the stomatal characteristics changed significantly among species, which could provide a theoretical basis for species identification.