ObjectiveBy observing and analyzing the rhizome structure and development characteristics of different varieties of peony, the anatomical study on the rhizome was conducted to preliminarily analyze the secondary structure and growth ring characteristics of the rhizome of herbaceous peony, so as to provide theoretical basis for judging the plant age of peony and optimizing the asexual reproduction and cultivation management technology, and promote the development and utilization of resources.

MethodThe underground rhizomes of different developmental stages of six varieties of different peony groups were studied, and their development and renewal characteristics were observed and analyzed. Paraffin sections and freehand slicing techniques were used to observe and analyze the secondary structural characteristics of rhizomes of different cultivars and different cultivars with varied growth years.

ResultThe underground rhizome structure of different varieties was basically the same, that is, the underground organs of the peony were composed of rhizome, rhizome buds and roots growing on the rhizome. The rhizome was updated regularly every year, and the age grading characteristics were obvious; the developmental characteristics of the tetraploid cultivar ‘Cream Delight’ were significantly different from the other five varieties.The rhizomes of 6 varieties of peony were composed of peridermis, cortex, secondary phloem, cambium, secondary xylem and central pith. The large and small conduits of the secondary xylem of the rhizomes of diploid variety ‘Zhongshengfen’, diploid variety ‘Fenyunu’, triploid variety ‘Coral Sunset’ and tetraploid variety ‘Cream Delight’ were arranged sequentially.The larger diameter catheter and the surrounding small catheter gathered to form a cluster, and the catheter group was sparsely distributed. The spacing between the two catheter groups was significant. The interval between the catheter clusters of ‘Coral Sunset’ was smaller than ‘Cream Delight’.The large and small ducts in the secondary xylem of the rhizomes of the two triploid Itoh varieties ‘Prairie Charm’ and ‘Going Bananas’ were evenly distributed and formed a relatively continuous ring zone, and they don’t clump together. After dehydration, the vascular structure of the rhizome of the peony was white or yellowish, with intermittent distribution of the ring, and the central medullary tissue was concave. Vascular tissues located in different rings were radially arranged from the pith to the cortex. The larger diameter catheters in the secondary xylem and the small ones around them were clustered in clumps in the rhizomes of different growth years. The catheter group was tangentially intermittently arranged in a sequence parallel to the cambium to form a clear growth ring, and the number of growth ring was consistent with the actual growth age of the rhizome of the herbaceous peony.

ConclusionThe structural characteristics of underground rhizome of different varieties of peony are basically the same, and there are obvious grading characteristics. The rhizome development characteristics of diploid and triploid are similar, but different from tetraploid. The secondary structural characteristics of rhizome of varieties belonging to lactiflora and hybrid groups are similar, but are significantly different in the varieties of Itoh group. There are significant differences in secondary structure of the rhizomes between triploid and tetraploid varieties of hybrid groups, and there is no direct correlation between the secondary structure characteristics of growth ring of rhizome and chromosome ploidy of herbaceous peony. The growth rings in the rhizome of herbaceous peony are its annual rings, and the number of growth rings can reflect the actual growth years of herbaceous peony.