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Herbaceous peony (Paeonia lactiflora Pall.) is a horticulturally important ornamental species that is widely cultivated in China. Biotic stress can strongly affect the quality and seed yield of herbaceous peony. Powdery mildew caused by the fungus Erysiphe polygoni is a serious biotic stress factor resulting in great losses to the peony cultivation industry. Although the molecular mechanisms underlying powdery mildew resistance have been studied extensively in various plant species, little is known about these mechanisms in P. lactiflora. In this study, we investigated the expression patterns of genes, using transcriptome profiling. During the expressed genes, we mainly focused on key TF genes that exhibited at least a log2 fold change ≥5 difference in expression level. The identified TFs genes were most belonged to the Zn-clus, C2H2, and MYB TF families. Furthermore, we examined the expression patterns of transcription factor genes in susceptible and resistant herbaceous peony varieties and identified a set of transcription factor genes that are differentially expressed in leaves in response to powdery mildew infection Based on our result, the MYB TF Pl10128 plays a critical role in defense against powdery mildew in herbaceous peony, and the AP2 TF Pl52977 is a negative regulator in response to powdery mildew of resistant variety ‘Ling Long Yu’. Taken together, this work will contribute the key transcription factors that might enhance plant immunity by controlling the expression of downstream defense-related gene.

Currently flower color in Hosta is limited to purple and white with some variation across species and cultivars in patterning of the two colors. This study was undertaken to determine the contributions of anthocyanins to current Hosta flower colors and to investigate the potential for increasing color diversity. Eighty-six hostas (6 species and 80 cultivars) were used in this study to investigate the composition and content of anthocyanins by high-performance liquid chromatography coupled with diode array detection (HPLC-DAD) and high-performance liquid chromatographic with electro spray ionization and mass spectrometry (HPLC–ESI–MS). The results showed that the color variation was low in the tepals of the genus of Hosta. Nine anthocyanins were initially identified using a typical purple cultivar (H. ‘Nakaimo’) and a white species (Hosta montana) The anthocyanins were delphinidin 3,5-O-diglucoside (Dp3G5G), cyanidin 3,5-O-diglucoside(Cy3G5G), petunidin 3,5-O-diglucoside (Pt3G5G), peonidin 3-O-rutinoside-5-O-glucoside (Pn3Ru5G), malvidin 3-O-rutinoside-5-O-glucoside (Mv3Ru5G), malvidin 3,5-O-diglucoside (Mv3G5G), petunidin 3-O-rutinoside (Pt3Ru), peonidin 3-O-rutinoside (Pn3Ru) and malvidin 3-O-rutinoside (Mv3Ru). Anthocyanin types and content were different between the purple flowered hostas (PFH) and the white flowered hostas (WFH, including white flower with purple spots or streaks): PFH had higher levels of anthocyanins and were correlated with the pigments Mv3Ru5G, Mv3G5G, Pt3G5G and Dp3G5G; WFH had lower levels of anthocyanins and were correlated with the pigments Pt3Ru, Pn3Ru, Mv3Ru and Pn3Ru5G. The dominance of Mv3G5G and Mv3Ru5G was responsible for flowers of simplex purple. Path analysis showed that Mv3G5G had the highest direct effect on lightness (L*), and color balance (a* and b*), while Pt3G5G had the highest direct effect on saturation (C*).

Volatile organic components in petals of thirty tree peony cultivars were analyzed using a headspace solid-phase microextraction technique (HS-SPME) coupled with GC–MS. 146 volatile organic components were detected, in which 81 of them were scent components. The major scent components were terpenes, alcohols, arenes and alkanes. According to major fragrances and the results of sensory evaluation, thirty cultivars were classified into five fragrance patterns: a woody scent, a rose scent, a lily of the valley scent, a phenolic scent and an unidentified scent, in which cis -ocimene, d -citronellol, linalool, 1,3,5-trimethoxybenzene (TMB) and pentadecane were their major floral fragrances, respectively. Seven cultivars were evaluated for their potential in the development and utilization of tree peony flowers: ‘Tian Xiang’, ‘Lan Bao Shi’, ‘Dian Jiang Feng Dan’, ‘Bai He Zhan Chi’, ‘Chun Xue’, ‘Hu Die Bao Chun’ and ‘High Noon’. In particular, ‘High Noon’ has significant high fragrance content for breeding fragrant peonies.

Petal coloration and anthocyanin compositions of 41 herbaceous peony cultivars were analyzed. Anthocyanins were identified by high-performance liquid chromatography–electrospray ionization-mass spectrometry (HPLC–ESI-MSn) coupled with photodiode array detection (DAD). Peonidin-3,5-di-O-glucoside (Pn3G5G), pelargonidin-3,5-di-O-glucoside (Pg3G5G), cyanidin-3,5-di-O-glucoside (Cy3G5G), peonidin-3-O-glucoside (Pn3G), and cyanidin-3-O-glucoside (Cy3G) were the five major anthocyanins in herbaceous peony cultivars. Deep purple or reddish purple cultivars contained 4–5 anthocyanins, whereas pink cultivars only contained Cy3G5G and Pn3G5G, and their contents were much lower than those of purple cultivars. According to the chemical structures of three anthocyanidins in association with petal coloration, flowers were classified into three phenotypes: 1. “Pn, Cy, and Pg” (all purple flowers including two pink flowers); 2. “Pn, Cy” (pink flowers); 3 “Pn” (light pink and white flowers). The coloration mechanisms of cultivars with the pink and purple flowers were quite different. Correlations between lightness (L*) and chroma (C*), chromatic component a* and total anthocyanins (TA) value, a* and co-pigmentation index (CI) showed opposite tendencies, whereas L* and TA showed the same tendency in each group. High contents of Pn3G5G and Pg3G5G may responsible for the purple coloration of herbaceous peony cultivars.

Bud sports have been widely exploited for creating novel cultivars in vegetatively propagated plants. However, bud sports of tree peony have rarely occurred nor been applied to breeding. We used sequence related amplified polymorphism (SRAP) markers to characterize two tree peony groups with bud sports. ‘Er Qiao’ and ‘Luo Yang Hong’ formed group I and are derived from Chinese cultivars, while ‘Shima-nishiki’ and ‘Taiyō’ formed group II and are related to Japanese cultivars. The DNA samples were evaluated with 25 different primer pairs. This resulted in a total of 149 different amplicons in Group I, of which 80.5% were polymorphic. Group II generated a total of 57 amplicons, of which 63.2% were polymorphic. The two groups shared 43 amplicons. The genetic similarity among the cultivars ranged from 0.33 to 0.60. The two bud sports groups were apparently separated on the unweighted pair-group method with arithmetic averages cluster analysis tree. The results demonstrated that this marker system appeared effective in detecting molecular differences between original parents and their bud sports in tree peony. This study provides a technical base for characterizing plants with bud sports, which are valuable genetic resources for further breeding.

A comparison in non-blotches and blotches of 35 cultivars of Xibei tree peony was investigated to explore flower coloration of Xibei tree peony (the second cultivar group in Chinese tree peony). With high performance liquid chromatography (HPLC) analysis, six anthocyanins including peonidin 3,5-di-O-glucoside (Pn3G5G), peonidin 3-O-glucoside (Pn3G), cyanidin 3,5-di-O-glucoside (Cy3G5G), cyanidin 3-O-glucoside (Cy3G), pelargonidin 3,5-di-O-glucoside (Pg3G5G), and pelargonidin 3-O-glucoside (Pg3G) were detected in non-blotches and blotches of petals. Total anthocyanins (TA), total flavones and flavonols (TF), and the copigmentation index (CI) were also analyzed. Cyanidin-based glycosides, which accumulated abundantly at the basal petal, resulted in blotch formation. Some peculiar cultivars with only one kind of anthocyanins or without anthocyanins in non-blotches were found in this study. For example, ‘Feng Zi Xiu Se’, ‘Ou Duan Si Lian’, and ‘Xi Wang’ contained only Pn3G5G; ‘Bing Shan Cang Yu’ and ‘Jin Bo Dang Yang’ contained only Cy3G; while no anthocyanins were found in ‘Bing Shan Xue Lian’. Several cultivars were rich in Pg-based glycosides, such as ‘Ni Hong Huan Cai’, and ‘Ju Yuan Shao Nv’. These cultivars would be excellent parents for creating new cultivars with novel flower color in the future.