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Currently, the use of anti-stress elicitors such as melatonin, N-acetyl-5-methoxytryptamine, is known as an effective method to reduce the negative impacts of stressful environments. Therefore, a two factor- five level (irrigation levels: 25–75% field capacity (FC) and melatonin: 0-300 mM) dry yield optimization and modeling were done using central composite design, essential oil quantity and quality, total phenol, flavonoid and chlorophyll content and also some physiological properties of grapefruit mint ( Mentha suaveolens × Mentha piperita ). The results showed that the grapefruit mint biomass in severe drought stress was reduced by 73% in comparison with normal irrigation. However, the application of 155 mM melatonin enhanced biomass yield, phenol, flavonoid, essential oil content and essential oil yield by 92.2, 33.4, 55.1, 45.3 and 143%, in comparison with control. Optimization analysis predicted that under FC 65% irrigation level and application of 240 mM melatonin would positively assist in achieving the maximum chlorophyll, phenol, flavonoid content and essential oil yield of grapefruit mint. In addition, the maximum content of linalool and linalool acetate was observed in FC 50% treated with 155 mM melatonin. Generally, it can be concluded that the application of melatonin, especially in 155 mM level, improved plant growth, essential oil quantity and quality and also plant physiological characteristics under drought stress.

Intercropping of medicinal plants/legumes along with bio-fertilizer application is a relatively new sustainable practice for improving the yield and secondary metabolites production. Here, a 2-years field experiment was performed to evaluate the effects of water deficit stress and arbuscular mycorrhizal fungi (AMF) application (as bio-fertilizer) on nutrients concentration, dry matter yield, essential oil quantity and quality of thyme in intercropping with soybean. Three irrigation levels, including (i) irrigation after depletion of 20% (I 20 ) as non-stressed, 50% (I 50 ) as moderate water deficit and 80% (I 80 ) available water as severe water deficit were applied as the main factor. The sub-factor was represented by different cropping patterns including thyme sole culture, replacement intercrop ratio of 50:50 and 66:34 (soybean: thyme) and the third factor was non-usage (control) and usage of AMF. According to our results, the thyme dry yield under moderate and severe water deficit stress decreased by 35 and 44% in the first year, and by 27 and 40% in the second year compared with non-stressed (I 20 ) plants, respectively. Also, the macro- and micro-nutrients of thyme leaves increased significantly in intercropping patterns after application of AMF. The maximum essential oil percentage of thyme was achieved in 50:50 intercropping ratio treated with AMF. Under moderate and severe water deficits, the major constituents of thyme essential oil including thymol, p -cymene and γ -terpinene were increased in intercropping patterns treated with AMF. Generally, AMF application in intercropping ratio of 50:50 may be proposed to farmers as an eco-friendly approach to achieve desirable essential oil quality and quantity in thyme under water deficit stress conditions.

The Climate Suitability Index (CSI) can increase agricultural efficiency by identifying the high-potential areas for cultivation from the climate perspective. The present study develops a probabilistic framework to calculate CSI for rainfed cultivation of 12 medicinal plants from the climate perspective of precipitation and temperature. Unlike the ongoing frameworks based on expert judgments, this formulation decreases the inherent subjectivity by using two components: frequency analysis and Particle Swarm Optimization (PSO). In the first component, the precipitation and temperature layers were prepared by calculating the occurrence probability for each plant, and the obtained probabilities were spatially interpolated using geographical information system processes. In the second component, PSO quantifies CSI by classifying a study area into clusters using an unsupervised clustering technique. The formulation was implemented in the Lake Urmia basin, which was distressed by unsustainable water resources management. By identifying clusters with higher CSI values for each plant, the results provide deeper insights to optimize cultivation patterns in the basin. These insights can help managers and farmers increase yields, reduce costs, and improve profitability.

Drought stress is one of the most significant environmental challenges, leading to various changes in the physiological processes of plants. Gamma-aminobutyric acid (GABA) is an essential biomolecule that plays a critical role in regulating growth and stress signaling. The current study aims to investigate the effects of GABA on antioxidant enzyme activity and the essential oil composition of Thymus daenensis Celak under different levels of water deficit stress. We examined three different levels of soil moisture (90%, 60%, and 30% of field capacity) alongside three GABA foliar treatments (0 mM, 25 mM, 50 mM, and 75 mM). The results showed that applying 25 mM GABA under severe stress conditions (at 30% of field capacity) significantly increased the activity levels of ascorbate peroxidase, guaiacol peroxidase, and superoxide dismutase enzymes by 95.5%, 78.45%, and 38%, respectively. Additionally, applying GABA at various levels during different water stress treatments led to significant improvements in the chlorophyll, carotenoid, and proline content in leaf tissues. Specifically, the application of 25, 50, and 75 mM GABA enhanced the proline content in T. daenensis by 53.9%, 26.8%, and 11%, respectively, compared to the control group (non-application of GABA). Essential oil analysis revealed the following ranges: thymol was present in the range of 38.07–45.18%, cymene in the range of 5.13–14.10%, caryophyllene in the range of 4.3–23.01%, and cineole in the range of 2–4.15%. The highest amount of thymol was obtained in the absence of GABA at 30% field capacity, while the greatest amount of cymene was also observed without GABA at 90% field capacity. Additionally, the maximum concentration of caryophyllene was found when 50 mM GABA was applied at 90% field capacity, and the maximum level of cineole was detected with 75 mM GABA at 90% field capacity. In conclusion, the exogenous application of GABA demonstrated favorable efficacy, particularly at a concentration of 25 mM. This treatment resulted in a significant enhancement of the plant's defense mechanisms and created favorable conditions that notably impacted the quality of the essential oil produced by T. daenensis .

Background Mentha longifolia L. is a perennial plant belonging to the Lamiaceae family that has a wide distribution in the world. M. longifolia has many applications in the food and pharmaceutical industries due to its terpenoid and phenolic compounds. The phytochemical profile and biological activity of plants are affected by their genetics and habitat conditions. In the present study, the content, constituents and antifungal activity of the essential oil extracted from 20 accessions of M. longifolia collected from different regions of Iran and Iraq countries were evaluated. Results The essential oil content of the accessions varied between 1.54 ± 0.09% (in the Divandarreh accession) to 5.49 ± 0.12% (in the Khabat accession). Twenty-seven compounds were identified in the essential oils of the studied accessions, which accounted for 85.5-99.61% of the essential oil. The type and amount of dominant compounds in the essential oil were different depending on the accession. Cluster analysis of accessions based on essential oil compounds grouped them into three clusters. The first cluster included Baziyan, Boukan, Sarouchavah, Taghtagh, Darbandikhan, Isiveh and Harir. The second cluster included Khabat, Kounamasi, Soni and Mahabad, and other accessions were included in the third cluster. Significant correlations were observed between the essential oil content and components with the climatic and soil conditions of the habitats. The M. longifolia essential oil indicated antifungal activity against Fusarium solani in both methods used. In all studied accessions, the fumigation method compared to the contact method was more able to control mycelia growth. In both methods, the inhibition percentage of essential oil on mycelia growth increased with an increase in essential oil concentration. Significant correlations were found between the essential oil components and the inhibition percentage of mycelium growth. Conclusion The studied M. longifolia accessions showed significant differences in terms of the essential oil content and components. Differences in phytochemical profile of accessions can be due to their genetic or habitat conditions. The distance of the accessions in the cluster was not in accordance with their geographical distance, which indicates the more important role of genetic factors compared to habitat conditions in separating accessions. The antifungal activity of essential oils was strongly influenced by the essential oil quality and concentration, as well as the application method. Determining and introducing the elite accession in this study can be different depending on the breeder’s aims, such as essential oil content, desired chemical composition, or antifungal activity.

Oregano ( Origanum vulgare L.) is a rich source of biologically active components such as phenolic compounds. Here, seven pot grown O. vulgare accessions belonging to three subspecies (subsp. virens , subsp. vulgare and subsp. gracile ) were investigated for their content in sixteen bioactive phenolic compounds as well as their antioxidant capacities (DPPH • and FRAP tests), total phenolic content (TPC) and total flavonoid content (TFC) in order to identify the most suitable ones on an industrial level. HPLC analyses showed that rosmarinic acid (659.6–1646.9 mg/100 g DW) was by far the most abundant constituent, followed by luteolin (46.5–345.4 mg/100 g DW), chicoric acid (36.3–212.5 mg/100 g DW), coumarin (65.7–193.9 mg/100 g DW) and quercetin (10.6–106.1 mg/100 g DW), with variability in concentration depending on the accession and subspecies. The highest level of rosmarinic acid and TPC was obtained from Ardabil accession (subsp. virens ). There was a significant and positive correlation between rosmarinic acid and antioxidant activity (r = 0.46). TFC significantly correlated to TPC (r = 0.57) as well as to chicoric acid (r = 0.73). Cluster (CA) and principal component (PCA) analyses classified the investigated accessions in three different groups. Such natural variabilities in phenolics provide the possibility of using elite plants for nutraceutical and pharmaceutical industries and domestication of highly antioxidative accessions of oregano.

Salinity, a severe worldwide issue, compromises the economic production of medicinal plants including mints and causes drug-yield decline. γ-Aminobutyric acid (GABA) is a tolerance-inducing signaling bio-molecule in various plant physiological processes. Pineapple mint ( Mentha suaveolens Ehrh.) is a valuable medicinal herb with an exhilarating scent of citrus fruit. Piperitenone oxide is the major bioactive constituent of its essential oil, having significant demand by pharmaceutical industries. Nonetheless, modeling and optimizing the effective concentration of GABA remain within twin foci of interest. Therefore, a two factor-five level (NaCl 0-150 mM and GABA 0-2.4 mM) central composite design was conducted to model and optimize drug yield and physiological responses of M . suaveolens . Based on the design of experiments (DoE) approach, different linear, quadratic, cubic, and quartic models were assigned to the response variables. Change trends of shoot and root dry weights followed a simple linear model, whereas sophisticated models (i.e., multiple polynomial regression) were fitted to the other traits. NaCl stress inevitably reduced root and shoot dry weight, piperitenone oxide content, relative water content, pigments content, and maximum quantum yield of PSII. However, content of malondialdehyde (MDA) and total flavonoid, and DPPH radical scavenging activity were increased under salinity. Under severe NaCl stress (150 mM), the essential oil content (0.53%) was increased three times in comparison with control (0.18%). Optimization analysis demonstrated that the highest amount of essential oil (0.6%) and piperitenone oxide (81%) as a drug yield-determining component would be achievable by application of 0.1–0.2 mM GABA under 100 mM NaCl. The highest dry weight of root and shoot was predicted to be achieved at 2.4 mM GABA. Overall, extremely severe NaCl stress (i.e., more than 100 mM) in which a sharp drop in yield components value was observed seemed to be out of M. suaveolens salinity tolerance range. Hence, it is rationale to compensate the decrease of drug yield by foliar application of a dilute GABA solution (i.e., 0.1–0.2 mM) under 100 mM NaCl stress or lower levels.

Background Oregano ( Origanum vulgare L.), one of the important medicinal plants in the world, has valuable pharmacological compounds with antimicrobial, antiviral, antioxidant, anti-inflammatory, antispasmodic, antiurolithic, antiproliferative and neuroprotective activities. Phenolic monoterpenes such as thymol and carvacrol with many medical importance are found in Oregano essential oil. The biosynthesis of these compounds is carried out through the methyl erythritol-4 phosphate (MEP) pathway. Environmental stresses such as salinity might improve the secondary metabolites in medicinal plants. The influence of salinity stress (0 (control), 25, 50 and 100 mM NaCl) on the essential oil content, composition and expression of 1-deoxy-D-xylulose-5-phosphate reductoisomerase ( DXR ), γ-terpinene synthase ( Ovtps2 ) and cytochrome P450 monooxygenases ( CYP71D180 ) genes involved in thymol and carvacrol biosynthesis, was investigated in two oregano subspecies ( vulgare and gracile ). Results Essential oil content was increased at low NaCl concentration (25 mM) compared with non-stress conditions, whereas it was decreased as salinity stress intensified (50 and 100 mM). Essential oil content was significantly higher in subsp. gracile than subsp. vulgare . The highest (0.20 mL pot −1 ) and lowest (0.06 mL pot −1 ) amount of essential oil yield was obtained in subsp. gracile at 25 and 100 mM NaCl, respectively. The content of carvacrol, as the main component of essential oil, decreased with increasing salinity level in subsp. gracile, but increased in subsp. vulgare . The highest expression of DXR , Ovtps2 and CYP71D180 genes was observed at 50 mM NaCl in subsp. vulgare . While, in subsp. gracile , the expression of the mentioned genes decreased with increasing salinity levels. A positive correlation was obtained between the expression of DXR , Ovtps2 and CYP71D180 genes with carvacrol content in both subspecies. On the other hand, a negative correlation was found between the expression of CYP71D180 and carvacrol content in subsp. gracile . Conclusions The findings of this study demonstrated that both oregano subspecies can tolerate NaCl salinity up to 50 mM without significant reduction in essential oil yield. Also, moderate salinity stress (50 mM NaCl) in subsp. vulgare might increase the carvacrol content partly via increment the expression levels of DXR , Ovtps2 and CYP71D180 genes.

Considering the significance of fenugreek as a valuable medicinal and food plant, assessing the genetic diversity of different populations of this species is essential for optimizing performance and adaptability to environmental conditions. This study aims to investigate genetic diversity and identify important phenotypic traits in various Iranian fenugreek accessions (“Mashhad”, “Tehran”, “Yazd”, “Shiraz”, “Birjand”, “Isfahan”, “Kerman”, “Kalat”, “Neyshabur”), an experiment was conducted in a randomized complete block design with three replications and nine treatments (accessions) in Iran. The results showed that the highest seed yield was observed in “Kalat” (120.73 g/m 2 ) and the lowest seed yield was observed in “Neyshabur” (29.28 g/m 2 ) accessions. Also, “Isfahan” had the highest number of branches (10.8/plant), and the highest 1000-seed weight (29.6 g) was recorded in “Shiraz”. It was also found that the number of days to the appearance of the first flower and the arrival of the last pod was the least in the “Yazd” (50 and 85 days) and the highest in the “Kerman” (87.67 and 170 days), respectively. It was also found that the highest content of soluble sugar (0.32%) belonged to the “Mashhad” and the highest amount of total chlorophyll (2.36 mg/gfw) belonged to the “Isfahan” accessions. “Birjand” had the highest antioxidant activity (55.64%). The highest abundance of bluish spots was also seen in the “Kalat” accession. The results of this study showed a considerable diversity between the studied accessions. The most suitable accession for harvesting seeds was “Kalat” and the “Isfahan” accession was the most appropriate for harvesting herbal yield. The results of this study provide a valuable foundation for future research aimed at identifying specific genotypes with superior traits, such as higher yield or stress resistance. Future studies can build upon these findings by focusing on selecting and breeding elite fenugreek lines for use in crop improvement programs.

Salinity is an abiotic stress that negatively affects plant growth and the synthesis of secondary metabolites. This study aimed to evaluate the effects of foliar applications of titanium (Ti) and nano-titanium (nano-Ti) at concentrations of 0, 50, and 100 mg/L under salinity levels of 0, 50, and 100 mM NaCl in controlled greenhouse conditions. A factorial experiment based on a completely randomized design with four replications was conducted. A comprehensive set of morphological (plant height, fresh and dry biomass), physiological (photosynthetic pigments, soluble carbohydrates, proline, and protein content), and biochemical parameters (antioxidant enzyme activities including superoxide dismutase, guaiacol peroxidase, and ascorbate peroxidase), as well as essential oil (EO) content and composition, were assessed. Salinity stress markedly reduced plant growth, chlorophyll content, and EO yield, while increasing oxidative stress markers such as malondialdehyde (MDA) and hydrogen peroxide (H₂O₂). The application of 100 mg/L nano-titanium under non-stress conditions significantly increased plant height (47.01 cm), fresh weight (87.33 g), and essential oil yield (0.639 g/pot). Moreover, essential oil content reached a maximum of 1.84% under 50 mM salinity with 100 mg/L nano-titanium, representing a 212% increase compared to the control. Nano-titanium application under salinity stress increased APX and SOD activities by 176% and 237%, respectively, compared to the control. GC–MS analysis revealed linalool, trans-caryophyllene, 1,8-cineole, and germacrene D as the major EO constituents, whose concentrations were notably influenced by both salinity level and Ti treatments. These findings suggest that nano-Ti has the potential to be used as a sustainable biostimulant to enhance growth and secondary metabolite production in M.  ×  gracilis under saline environments.