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Jianjun Zhang, Wei Zhu, Jaime A. Teixeira da Silva, Yongming Fan, and Xiaonan Yu

The analysis of herbaceous peony (Paeonia lactiflora Pall.) floral bud initiation and differentiation from autumn to early spring is important because flower formation is strictly correlated with flowering in late spring. A clear understanding of peony flower development would allow management practices to be optimized for stable annual production and supply of cut flowers. The aim of this research was to study the time-sensitive characteristics underlying flower development in peony cultivar ‘Dafugui’. Flower bud differentiation was assessed by paraffin and hand-made slices, as well as stereomicroscopy. Both methods have strengths and weaknesses. Our observations are not entirely consistent with those of previous studies. Flower bud differentiation in ‘Dafugui’, which starts from late September to mid-April of the following year, is divided into differentiation of the lower parts (separate differentiation periods for the bracts, sepals, petals, stamens, and pistillodes) and upper parts (separate differentiation periods for the petals, stamens, and pistil), and is closely related to annual changes in ambient temperature. Differentiation of lower flower buds takes place before winter dormancy, whereas that of upper parts starts early in the following spring, and finally forms a double-flowered type. The three methods used in this article can be used to study P. lactiflora flower bud differentiation and can contribute to an understanding of this process in the future.

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Lihong Hao, Hui Ma, Jaime A. Teixeira da Silva, and XiaoNan Yu

The pollen morphology of 26 cultivars of herbaceous peony (Paeonia L.) was examined by scanning electron microscopy (SEM). Pollen grains of the cultivars were mostly subprolate to perprolate, tricolporate, or ellipsoidal in equatorial view, but rounded-trifid in polar view. The poles of pollen grains were mainly flat when viewed in cross-section and only a few appeared to have a circular or arc shape. In addition, the surface of the pollen grains was psilate, and the muri were partly or fully protuberant with a reticulate surface sculpture. However, the shapes and sizes of pollen grains as well as surface ornamentation varied significantly among cultivars with different chromosome numbers. The pollen grains from diploid cultivars were regular and full, and the reticulation holes were evenly distributed, while most of the pollen grains from triploid cultivars were empty flat shells with some heteromorphic pollen whose surface ornamentation was mostly rugulate-reticulate exine. The pollen grains from tetraploid cultivars were the largest although pollen morphology and surface ornamentation differed between Athena and Cream Delight. Six indices [polar axis length (P), equator axis length (E), P/E, pollen perforation diameter (D), ridge width (W), and D/W] were used in Q cluster analysis, which divided the 26 cultivars into three groups. Group I included eight diploid, four triploid, and one tetraploid cultivar. Group II included 12 triploid cultivars with complex genetic backgrounds. Group III included only one tetraploid cultivar Cream Delight. This work may provide an important palynological basis for studying taxonomy and hybrid breeding of herbaceous peony cultivars.

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Qi Wang, Rui Zhao, Qihang Chen, Jaime A. Teixeira da Silva, Liqi Chen, and Xiaonan Yu

Herbaceous peony is a perennial flowering plant with strong environmental adaptability and may be a good candidate for culture in arid areas. In this study, the physiological and biochemical responses of two herbaceous peony cultivars to different soil moisture gradients in pots were assessed by analyzing changes in 13 stress-related indices. The drought damage index (DDI) and the contents of malondialdehyde (MDA), soluble sugar, proline, and abscisic acid (ABA) generally increased as drought stress intensified, whereas leaf relative water content (LRWC) decreased, and the contents of soluble protein, indole-3-acetic acid (IAA), the ratio of IAA and ABA, and the activities of four antioxidant enzymes fluctuated. For the leaves, a positive correlation was found between DDI and superoxide dismutase (SOD), MDA, soluble sugar, proline, ascorbate peroxidase (APX), and ABA, but it was negatively correlated with LRWC, peroxidase (POD), and catalase (CAT). In fibrous roots, DDI was positively correlated with MDA, soluble sugar, proline, soluble protein, and ABA but was negatively correlated with SOD, CAT, APX, and IAA/ABA. Principal component analysis and subordinate functions were used to evaluate drought resistance of the two cultivars, with ‘Karl Rosenfield’ showing greater resistance to drought than ‘Da Fu Gui’.

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Chaowei Song, Qi Wang, Jaime A. Teixeira da Silva, and Xiaonan Yu

Thirty herbaceous peony (section Paeonia of the genus Paeonia) cultivars were divided into four groups (no fragrance, light fragrance, medium fragrance, or intense fragrance) based on their sensory evaluation scores. Using dynamic headspace sampling (DHS) and automatic thermal desorption–gas chromatography/mass spectrometry (ATD-GC/MS), 130 volatile organic components were detected in these 30 cultivars and a total of 72 compounds were identified as scent components. The main compounds were phenylethyl alcohol, β-caryophyllene, linalool, (R)-citronellol, and nerol. Selecting α-pinene as the standard, the volatile components of these cultivars were quantitatively analyzed. By combining the sensory evaluation scores and the results of quantitative analysis, we found that ‘Going Bananas’, ‘Cream Delight’, ‘Zhu Sha Pan’, ‘Qiao Ling’, ‘Duchess de Nemours’, and ‘Yang Fei Chu Yu’ displayed an intense fragrance and, thus, had relatively high commercial value for the flower fragrance industry. ‘Red Magic’, ‘Joker’, ‘Fairy Princess’, ‘Lovely Rose’, ‘Carina’, and ‘Etched Salmon’ were excluded from the hierarchical cluster of aromatic compounds and the analysis of fragrance patterns because of the low amount of fragrance they released and poor sensory evaluation results. Based on a cluster analysis, assessment of the major aromatic compounds, and the results of sensory evaluation, the remaining 24 cultivars were divided into five fragrance patterns for the first time: woody scent [cluster I (major fragrance β-caryophyllene)], fruity scent [cluster II (phenylethyl alcohol)], lily scent [cluster III (linalool)], rose scent {cluster IV [(R)-citronellol]}, and an orange blossom scent [cluster V (nerol)].

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Liuhui Yang, Jianjun Zhang, Jaime A. Teixeira da Silva, and Xiaonan Yu

The karyotypes of 21 herbaceous peony (Paeonia) cultivars were studied using root tip squashes revealing a wide variety of ploidy levels. There were three tetraploid (2n = 4x = 20), 11 triploid (2n = 3x = 15), and one diploid (2n = 2x = 10) cultivars in the hybrid group; five triploid (2n = 3x = 15) cultivars in the Itoh group; and one diploid (2n = 2x = 10) cultivar in the lactiflora group (LG). The asymmetry index (AI) ranged from 59.61% (‘Cytherea’) to 64.03% (‘Little Red Gem’). The karyotypes of all peony cultivars were 2A with 60% metacentric (m), 20% submetacentric (sm), and 20% subtelocentric (st) chromosomes. The karyotypic background of these 21 herbaceous peony cultivars is discussed in the context of the evolution of ploidy and the three cultivar groups. These results provide cytological information that would assist in a peony hybridization program.