Continuous cropping (CC) is a common practice in agriculture, and usually causes serious economic losses due to soil degeneration, decreased crop yield and quality, and increased disease incidence, especially in medicinal plants. Continuous cropping obstacles (CCOs) are mainly due to changes in soil microbial communities, nutrient availability, and allelopathic effects. Recently, progressive studies have illustrated the molecular mechanisms of CCOs, and valid strategies to overcome them. Transcriptomic and metabolomics analyses revealed that identified DEGs (differently expressed genes) and metabolites involved in the response to CCOs are involved in various biological processes, including photosynthesis, carbon metabolism, secondary metabolite biosynthesis, and bioactive compounds. Soil improvement is an effective strategy to overcome this problem. Soil amendments can improve the microbial community by increasing the abundance of beneficial microorganisms, soil fertility, and nutrient availability. In this review, we sum up the recent status of the research on CCOs in medicinal plants, the combination of transcriptomic and metabolomics studies, and related control strategies, including uses of soil amendments, crop rotation, and intercropping. Finally, we propose future research trends for understanding CCOs, and strategies to overcome these obstacles and promote sustainable agriculture practices in medicinal plants.

Casparian strip membrane domain protein-like (CASPL) genes are key genes for the formation and regulation of the Casparian strip and play an important role in plant abiotic stress. However, little research has focused on the members, characteristics, and biological functions of the patchouli PatCASPL gene family. In this study, 156 PatCASPL genes were identified at the whole-genome level. Subcellular localization predicted that 75.6% of PatCASPL proteins reside on the cell membrane. A phylogenetic analysis categorized PatCASPL genes into five subclusters alongside Arabidopsis CASPL genes. In a cis-acting element analysis, a total of 16 different cis-elements were identified, among which the photo-responsive element was the most common in the CASPL gene family. A transcriptome analysis showed that p-hydroxybenzoic acid, an allelopathic autotoxic substance, affected the expression pattern of PatCASPLs, including a total of 27 upregulated genes and 30 down-regulated genes, suggesting that these PatCASPLs may play an important role in the regulation of patchouli continuous cropping obstacles by affecting the formation and integrity of Casparian strip bands. These results provided a theoretical basis for exploring and verifying the function of the patchouli PatCASPL gene family and its role in continuous cropping obstacles.

Codonopsis lanceolata is widely used in traditional medicine and diets. However, there is no optimal protocol for the commercial production of C. lanceolata seedlings. This study was carried out to find the optimum supplementary light source for the production of C. lanceolata seedlings. Seedlings were grown for four weeks in a glasshouse with an average daily light intensity of 490 μmol·m⁻²·s⁻¹ photosynthetic photon flux density (PPFD) coming from the sun and a 16-h daily supplementary lighting at 120 μmol·m⁻²·s⁻¹ PPFD from either high-pressure sodium (HPS), metal halide (MH), far-red (FR), white LED (LED-w), or mixed (white: red: blue = 1:2:1) LEDs (LED-mix). The results showed that the greatest total biomass, stem diameter, ratio of shoot weight to shoot length, root biomass, and ratio of root weight to shoot weight were found in seedlings grown under supplementary LED-mix. Meanwhile, the stomatal properties and soluble sugar contents were improved for seedlings in LED-mix. The contents of starch, total phenols, and flavonoids were the greatest for seedlings in LED-w and LED-mix. The expression of photosynthetic proteins and genes in seedlings was also enhanced by LED-mix. Overall, these results suggest that LED-mix is advantageous to the photosynthetic potential and the accumulation of biomass, carbohydrates and secondary metabolites in C. lanceolata.

Hydrogen sulfide (H₂S) is endogenously produced in plant cells and plays an essential role in root development. Given its potential for future agricultural applications, the optimal concentration of sodium hydrosulfide (NaHS, an H₂S donor) and the potential mechanisms for root development in the strawberry ‘Seolhyang’ were investigated in this study. The results showed that NaHS with a concentration of 1.250 mM had a positive effect on root development in strawberry. Further experiments showed that exogenous NaHS elevated the H₂S content in the root. The dry root weight was increased by the 1.250 mM NaHS treatment, but was reduced by the hypotaurine (an H₂S scavenger) treatment. Similar changes were found between H₂S and soluble sugar contents, indicating that H₂S enhanced the accumulation of soluble sugar. Therefore, it is suggested that the accumulation of soluble sugar induced by H₂S is either directly or indirectly involved in root development in strawberry during plug production. Moreover, superoxide dismutase was shown to have contributed to the elevated H₂O₂ contents. These results contribute to our understanding of the role that H₂S plays and some of the relevant mechanisms in which H₂S regulates root development.

Somatic embryogenesis is a preferred method for vegetative propagation due to its high propagation efficiency. In this study, zygotic embryos, cotyledons, and hypocotyls of Paeonia ostii ‘Fengdan’ were used as the explant to induce somatic embryogenesis. The results showed that a combination of 0.5 mg·L⁻¹ thidiazuron (TDZ) and 0.5 mg·L⁻¹ 2,4-dichlorophenoxyacetic acid (2,4-D) was effective in inducing somatic embryos from the zygotic embryo and cotyledon explants. Hypocotyls only formed somatic embryos on Murashige and Skoog (MS) medium supplemented with both 0.5 mg·L⁻¹ TDZ and 0.5 mg·L⁻¹ 1-naphthylacetic acid (NAA). Moreover, the compact callus was effectively produced from zygotic embryo, cotyledon, and hypocotyl explants in medium supplemented with a combination of 3.0 mg·L⁻¹ 6-benzylaminopurine (BA) and 1.0 mg·L⁻¹ NAA, and then converted into somatic embryos in the same medium, and the ratio of the explants with embryo induction and number of embryos induced per explant were much higher than those induced by 0.5 mg·L⁻¹ TDZ and either 0.5 mg·L⁻¹ 2,4-D or 0.5 mg·L⁻¹ NAA. The MS medium was better than the woody plant medium (WPM) for inducing somatic embryos from zygotic embryo and hypocotyl explants, whereas the WPM was better than the MS medium for somatic embryogenesis induction from cotyledon explants. All of the somatic embryos developed well into mature embryos on their respective media supplemented with both 3.0 mg·L⁻¹ BA and 1.0 mg·L⁻¹ NAA. Overall, the protocols for indirect somatic embryogenesis from zygotic embryo, cotyledon, and hypocotyl of P. ostii ‘Fengdan’ were successfully established, which can greatly facilitate their propagation and breeding processes.

Astragalus membranaceus and Codonopsis lanceolata are two important medical herbs used in traditional Oriental medicine for preventing cancer, obesity, and inflammation. Night temperature is an important factor that influences the plug seedling quality. However, little research has focused on how the night temperature affects the growth and development of plug seedlings of these two medicinal species. In this study, uniform plug seedlings were cultivated in three environmentally controlled chambers for four weeks under three sets of day/night temperatures (25/10 °C, 25/15 °C, or 25/20 °C), the same relative humidity (75%), photoperiod (12 h), and light intensity (150 μmol·m⁻²·s⁻¹ PPFD) provided by white LEDs. The results showed that night temperature had a marked influence on the growth and development of both species. The night temperature of 15 °C notably enhanced the quality of plug seedlings evidenced by the increased shoot, root, and leaf dry weights, stem diameter, and Dickson’s quality index. Moreover, a night temperature of 15 °C also stimulated and increased contents of primary and secondary metabolites, including soluble sugar, starch, total phenols and flavonoids. Furthermore, the 15 °C night temperature increased the chlorophyll content and stomatal conductance and decreased the hydrogen peroxide content. Analysis of the gene expression showed that granule-bound starch synthase (GBSS), ribulose bisphosphate carboxylase large chain (RBCL), and ferredoxin (FDX) were up-regulated when the night temperature was 15 °C. Taken together, the results suggested that 15 °C is the optimal night temperature for the growth and development of plug seedlings of A. membranaceus and C. lanceolata.