Tetraploid Induction with Leaf Morphology and Sunburn Variation in Sorbus pohuashanensis (Hance) Hedl

Sorbus pohuashanensis (Hance) Hedl. is an important forestry species valued for its ornamental, medicinal, and ecological properties. Polyploidy breeding is an important method of germplasm innovation; however, polyploidy induction and phenotypic variation caused by chromosome doubling in S. pohuashanensis are poorly understood. In this study, S. pohuashanensis seeds were used to explore the effects of different colchicine concentrations, cold stratification times, and seeds from different sources on polyploidy induction. Ploidy levels of the regenerated plants were determined by flow cytometry. The results showed that the tetraploid induction effect of S. pohuashanensis seeds was significantly affected by colchicine concentration, and the highest tetraploid induction rate of 24.75% was achieved by immersion in 0.2% (w/v) colchicine for 48 h. After 2 years of induction, 77 tetraploid plants were obtained. Compared to diploids, tetraploid plants showed significant variations in plant height, leaf morphology (apical leaflet width, middle leaflet width), and diameter of the middle petiole. The stomatal size and chloroplast number increased with chromosome doubling whereas the stomatal number and density decreased. In addition, significant differences in the percentage of sunburn associated with ploidy changes were observed. This study provides a technique for tetraploid induction of S. pohuashanensis seeds, showing the variation in traits caused by polyploidization and the effect of chromosome doubling on sunburn resistance. Tetraploidy induction provides a new direction for S. pohuashanensis germplasm innovation.