Dendrobium officinale Kimura et Migo is an orchid with both medicinal and edible values and a high economic value. The wild resources of D. officinale are in an endangered state. Compared with the wild D. officinale, cultivated D. officinale exhibits inferior quality and a low content of medicinal components. Polyploid induction is a conventional breeding tool for genome doubling of species, which can effectively increase the total amount of plant components to improve the medicinal efficacy of D. officinale. In this study, D. officinale tetraploids were generated by treating the protocorms with colchicine. Morphological observations showed that tetraploids exhibited decreased plant size and leaf shape index and increased stem diameter. Cytological observations showed that the polyploid plants had larger stomata and a lower number of stomata per unit area compared with normal plants. The highest stomata variation of 30.00% was observed when the plant was treated with 0.3% colchicine for 24 h. Chromosomal observations showed that treatment of plants with 0.2% colchicine for 48 h resulted in the highest tetraploid induction rate of 10.00%. A total of 10 tetraploids were successfully obtained by inducing plant protoplasts with colchicine. The number of diploid D. officinale chromosomes was 38 with a base number of 19, and the karyotype formula was 2n = 2x = 38 = 24m + 14sm with a karyotype asymmetry coefficient of 60.59%, belonging to type 2B. The number of tetraploid D. officinale chromosomes was 76 with a base number of 19, and the karyotype formula was 2n = 4x = 76 = 58m + 18sm with a karyotype asymmetry coefficient of 60.04%, belonging to type 2B. This study determined the optimal mutagenesis treatment based on the chromosome observation results, investigated the relationship between the phenotype and ploidy level, and generated the polyploid germplasm of D. officinale, thereby laying the foundation for the breeding of new D. officinale cultivars enriched with compounds of medicinal value.

The high temperature may cause difficult growth or bloom in the summer, which is the key problem limiting the cultivation and application of dahlia. The photosynthetic physiological mechanisms of dahlia under high temperature stress were studied to provide a theoretical basis for expanding the application range of cultivation and annual production. Two dahlia varieties, ‘Tampico’ and ‘Hypnotica Tropical Breeze’, were used as test materials and were treated for 1 d or 2 d at temperatures of 35/30 °C or 40/35 °C (day/night: 14 h/10 h) and then recovered at 25/20 °C for 7 d. A 25/20 °C treatment was used as the control. The results are as follows: (1) High-temperature stress resulted in the chlorophyll (Chl) content, Fv/Fm, transpiration rate (Tr), net photosynthetic rate (Pn), and water potential decreasing significantly, and the Chl content, Tr, and stomatal density of ‘Tampico’ were higher than those of ‘Hypnotica Tropical Breeze’ during the same period. (2) After the two dahlia varieties were treated with high-temperature stress and recovered at 25/20 °C for 7 d, the plant morphology and various physiological indices under the 35/30 °C treatment gradually returned to normal, with ‘Tampico’ in better condition than ‘Hypnotica Tropical Breeze’. (3) Both dahlia varieties could not withstand the stress of 40/35 °C for 2 days.

Background and Objectives: More frequent and severe droughts are occurring due to climate change in northern China. In addition to intensity and duration, the timing of droughts may be decisive for its impacts on tree growth, mortality, and the whole forest ecosystem. The aim of this study was to compare the effect of drought occurring in the early- and mid-growing season on the growth and physiology of Mongolian pine (Pinus sylvestris var. mongolica Litv.) saplings. Materials and Methods: Four-year-old container saplings that were about to sprout were exposed to three treatments: (i) regular irrigation throughout the growing season (CTRL), (ii) no irrigation in the early growing season (weeks 1–5) followed by regular irrigation (EGD), (iii) no irrigation in the mid growing season (weeks 5–10), and regular irrigation in the early and late growing season (MGD). We measured the root and shoot growth, sapling mortality, and the physiological changes in the roots and needles periodically. Results: Drought in the mid growing season was more harmful than in the early growing season in terms of chlorophyll fluorescence, electrolyte leakage of needles, needle length, stem diameter increment, and sapling mortality. The high mortality in the mid growing season might be attributed to the joint effect of drought and high temperature. Drought in the early growing season decreased root growth, and the starch and soluble sugars in roots as much as the drought in the mid growing season. Abscisic acid concentration increased in fine roots, but decreased in old needles after drought. Conclusions: Special attention should be paid on forest sites susceptible to drought during afforestation in the face of ongoing climate change.

The genus Dahlia has approximately 40 species; however, the complete chloroplast genome has been reported only for one species. Due to this lack of information on the chloroplast genomes, the phylogenetic relationships within the Dahlia genus remain unclear. Therefore, the present study sequenced the complete chloroplast genome of D. imperialis for the first time. This genome was 152,084 bp long with a typical quadripartite structure and a GC content of 38.45%. A total of 134 genes were annotated in the genome, including 86 protein-coding genes, 38 transfer RNA genes, 8 ribosomal RNA genes, and 2 pseudogenes. The detailed analysis identified UUA as the most frequently used codon and found 62 intergenic repeat sequences and 157 SSR loci in the D. imperialis genome. Phylogenetic analysis based on 49 chloroplast genomes showed that Dahlia was a monophyletic group, with D. imperialis positioned at the base of this clade. Network evolution and gene flow analysis unveiled extensive hybridization events within the Heliantheae alliance, especially in Dahlia. Thus, the comprehensive analysis of the complete chloroplast genome of D. imperialis enriches the information on the genetic resources of the Dahlia species, provides valuable information for reconstructing their phylogeny, and reveals the evolutionary dynamics of the Dahlia chloroplast genome.

Hybridization plays a crucial role not only in the origin and evolution of species but also in the formation of species diversity. Dendrobium is one of the largest genera in the Orchidaceae, exhibiting both a high rate of self-incompatibility (SI) and interspecific compatibility. However, there have been few reports on the distribution pattern of the SI and interspecific compatibility in Dendrobium and their relationship to the reticular evolution of Dendrobium. In this study, self- and cross-pollination experiments were conducted on selected Dendrobium species, and all previously reported data were integrated. The phylogenetic relationships of Dendrobium species were analyzed by using nuclear ITS sequence information and all published complete chloroplast genome data. SI and reticulate evolution were also studied for verification of their relationship to interspecific compatibility. The results showed that the SI rate in Dendrobium ranged from 55.64% to 70.96%, and species with self-incompatibility were widely distributed within the genus. Dendrobium species followed the SI × self-compatibility (SC) rule, suggesting SI affected the interspecific compatibility in Dendrobium. Further, when SC and SI/SC species served as parents, the rate of interspecific compatibility was higher than that with SI species as parents. The rate of interspecific compatibility (52.50%) between species or groups with closer reticulate evolutionary relationships was higher than that of all hybridization combinations (24.05%). Overall, this study provides new insights into the formation of high species diversity in Dendrobium and offers theoretical guidance for further hybridization breeding.

Temperature is a key determinant of flowering time and floral pigmentation in plants, and dahlia (Dahlia pinnata) is particularly sensitive to thermal changes in its flower color. This study investigated how day/night temperature regimes regulate flower bud differentiation and coloration in the potted cultivar ‘Hypnotica Tropical Breeze’. Five temperature treatments (15/5, 20/10, 25/15, 30/20, and 35 °C/25 °C) were applied, and flower bud differentiation progression, colorimetric traits, and pigmentation-related differentially expressed genes were assessed. The 15/5, 20/10, and 25 °C/15 °C treatments all allowed successful bud differentiation and flowering, yet the duration varied considerably—46 days at 20 °C/10 °C and 41 days at 25 °C/15 °C versus 100 days at 15 °C/5 °C. Among these three regimes, 20 °C/10 °C gave the highest a* (red–green axis, positive = red) and lowest b* (yellow–blue axis, positive = yellow) at the ray floret tips. Moreover, the relative flavonoid and anthocyanin indices, as well as soluble sugar and starch contents, were all highest at 20 °C/10 °C and lowest at 15 °C/5 °C, with significant differences across treatments. Transcriptomic analysis revealed pronounced differential expression of anthocyanin-biosynthetic genes (CHI2, F3H, DFR, ANS, UFGT) and transcription factors (bHLH, MYB) among the three temperature groups. In particular, UFGT transcript abundance was lowest at 15 °C/5 °C, and FNSII expression was also reduced under this regime relative to 20 °C/10 °C. Together, these findings indicate that day/night temperature regimes are linked to bud differentiation and color development in dahlia, together with shifts in sugar metabolism and pigment-related gene expression.