The artificial enlargement of the planting area and ecological amplitude of ornamentals for horticultural and landscape applications are significant. Herbaceous peony (Paeonia lactiflora Pall.) is a world-famous ornamental with attractive and fragrant flowers and is mainly planted in temperate and cool areas. Comparatively higher winter temperatures in the subtropical and tropical Northern Hemisphere result in a deficit of chilling accumulation for bud dormancy release, which severely hinders “The southward plantation of herbaceous peony”. Studies on the dormancy, chilling requirement (CR) and relevant molecular mechanisms of peony are needed to enhance our ability to extend the range of this valuable horticultural species. Based on natural and artificial chilling experiments, and chilling hour (CH) and chilling unit (CU) evaluation systems, the lowest CR of ‘Hang Baishao’ was between 504.00 and 672.00 CHs and the optimal CR was 672.00 CHs and 856.08 CUs for achieving strong sprouting, growth and flowering performance. Transcriptome sequencing and gene identification by RNA-Seq were performed on ‘Hang Baishao’ buds during the dormancy and sprouting periods. Six gene libraries were constructed, and 66 temperature- and photoperiod-associated unigenes were identified as the potential candidate genes that may regulate or possibly determine CR characteristics. The difference in the expression patterns of SUPPRESSPOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) between the winters of 2012–2013 and 2015–2016, and the difference of CR fulfillment periods also between these two winters represented the interesting congruent relationships. This correlation was also observed for WRKY DNA-BINDING PROTEIN 33 (WRKY 33). Combined with the results acquired from all of experiments, ‘Hang Baishao’ was confirmed to be a superb peony resource that have significantly low CR characteristics. The two genes of SOC1 and WRKY33 are likely involved in determining the CR amount and fulfillment period of ‘Hang Baishao’. HEAT SHOCK PROTEIN, OSMOTIN and TIMING OF CAB EXPRESSION 1 also deserve attention for the CR research. This study could contribute to the knowledge of the deep factors and mechanisms that regulate CR characteristics, and may be beneficial for breeding new germplasms that have low CRs for landscape or horticulture applications in subtropical regions.

Callus browning is a significant problem that hinders plant tissue regeneration in Paeonia ostii “Fengdan” by causing cell death and inhibiting growth. However, the molecular mechanism underlying callus browning in P. ostii remains unclear. In this study, we investigated the metabolites and potential regulatory genes involved in callus browning of P. ostii using metabolomic and transcriptomic analyses. We found a significant accumulation of phenolic compounds in the browned callus, represented by flavonoid compounds. Notably, the accumulations of luteotin and disomentin were higher in browning calli compared to non-browning calli. Transcriptomic analysis identified that candidate genes associated with flavonoid biosynthesis, including flavonoid 3-hydroxylase (PoF3H) and flavone synthase II (PoFNSII), were highly expressed in the browned callus of P. ostii “Fengdan”. Weighted gene co-expression network analysis (WGCNA) further highlighted that polyphenol oxidase (PoPPO) which encoded polyphenol oxidase, together with flavonoid biosynthesis-related genes such as flavanone 3-hydroxylase (PoF3H) and flavonone Synthase II (PoFNSII), as well as cellular totipotency-related genes wuschel-related homeobox 4 (PoWOX4), were involved in callus browning. Based on these findings, we proposed the molecular mechanism by which flavonoid accumulation, polyphenol oxidation, and cellular totipotency pathways contribute to callus browning in P. ostii. Our study provides new insights into the molecular mechanism underlying callus browning and offers the foundations to facilitate the establishment of an efficient plant tissue regeneration system in P. ostii.

Helleborus orientalis L. is a valuable winter-flowering and understory landscape plant, but its application and breeding are hindered by poor heat tolerance and the lack of a robust germplasm evaluation system. In this study, 51 Helleborus L. hybrid individuals obtained through manual open pollination were evaluated using coefficient of variation (CV), Shannon–Weaver diversity index (H′), correlation analysis, principal component analysis (PCA), and cluster analysis to assess genetic diversity and ornamental value based on 17 phenotypic traits. The results showed rich phenotypic diversity among the hybrids. Quantitative traits showed CV ranging from 9.48% to 37.99% and H′ between 0.77 and 1.51, with flower count and leaf length being the most variable. Qualitative traits had H′ values from 0.52 to 1.55, with sepal color showing the highest diversity. Significant correlations were detected among heat tolerance, pest resistance, leaf and petiole length, as well as plant and flower form. PCA extracted six principal components accounting for 74.50% of cumulative variance. Cluster analysis classified the 51 germplasms into five groups. Using the AHP model, a comprehensive evaluation system was established, and 13 elite individuals were selected for variety rights application and characterization. This study provides a reference for establishing DUS test guidelines and advancing breeding and utilization of Helleborus L.

Paeonia lactiflora Pall. (herbaceous peony) is a high-value ornamental and medicinal plant in China with considerable market potential. However, conventional propagation methods are limited by low multiplication rates and long production cycles, making it difficult to meet the demand for large-scale planting materials. As a key approach for rapid propagation, tissue culture techniques for P. lactiflora have achieved significant progress in recent years. This review summarizes advances in the tissue culture system for P. lactiflora over the past decade, focusing on major in vitro regeneration pathways (organogenesis and somatic embryogenesis) and crucial technical stages, including explant selection and culture environment optimization. Distinct from previous reviews that only introduce partial technical aspects of P. lactiflora tissue culture, this review comprehensively outlines the overall tissue culture system, analyses the current species-specific bottlenecks (browning, vitrification, rooting and acclimatization) with their underlying causes and proposes targeted strategies. Furthermore, future development trends are prospected by integrating emerging research directions, including molecular regulatory mechanisms and eco-adaptive breeding. This review aims to provide a theoretical foundation and technical support for obtaining propagule for commercial plantations and achieving multi-functional utilization of P. lactiflora.

Substrate composition plays a vital role in the soilless cultivation of Helleborus; high-quality substrates can create optimal growth conditions and enhance plant quality. However, knowledge regarding suitable substrates for Helleborus remains limited. The aim of the study was to test the effects of different substrates on growth of potted Helleborus × hybridus seedlings. In total, 12 treatments were formulated by mixing organic components (moss peat, cocopeat, domestic peat) with inorganic particles (perlite, kanuma soil, vermiculite) at a 1:1 ratio, using moss peat moss as the control. The results indicated that substrates of moss peat + vermiculite (1:1) and cocopeat + vermiculite (1:1) significantly promoted plant height, shoot number, leaf number, and root development. The treatment with domestic peat + perlite + kanuma soil + vermiculite (3:1:1:1) yielded the highest soluble protein content, whereas the CK group showed the highest soluble sugar content. A comprehensive evaluation by Principal Component Analysis (PCA) identified moss peat + vermiculite (1:1) as the optimal substrate, followed by coir + vermiculite (1:1). Considering economic costs and environmental protection factors, the cocopeat + vermiculite (1:1) mixture demonstrated superior potential. Collectively, our study clarifies the effects of different substrate compositions and provides new insights for achieving cleaner and more efficient soilless cultivation of Helleborus.