Two experiments (in Petri dishes and in soil) were conducted to investigate the effects of osmopriming on seed germination and the early seedling characteristics of caraway (Carum carvi L. var. annua). The priming treatments in the Petri dish experiment were: polyethylene glycol (5%, 10% and 20%), KNO₃ (0.5%, 1% and 2%) and KCL (1%, 2% and 4%) with three different soaking times (12, 24 and 36 h) along with control (non-primed seeds). Only polyethylene glycol and H₂O were applied in the cell tray experiment, which were then compared with the non-primed seeds. In the Petri dish experiment, all three priming reagents significantly enhanced seedling length, with the most effective treatments being 5% PEG, 2% KNO₃ and 1% KCL for 12 h. The plumule dry weights were also increased significantly after PEG (20% for 36 h), KNO₃ (2% for 24 and 36 h) and KCL (1% for 12 h) treatments in comparison with the control. In the soil experiment, osmopriming with PEG significantly improved the germination rate (GR) and percentage, the plumule dry and fresh weights and the plumule length of caraway seedlings when compared with the control. A 23% higher germination percentage was recorded for the seeds treated with 5% PEG for 24 h as compared with the non-primed seeds. The PEG-primed seeds produced significantly longer seedlings when treated with 5% PEG for 24 h. All of the applied PEG treatments significantly enhanced the plumule fresh and dry weights, with the best outcomes being after 5% PEG (24 h) and 10% PEG (36 h) treatments, respectively. The 12-h hydro-priming also significantly enhanced all of the studied germination parameters when compared to the control. The results of the presented experiments show the significant positive effects of seed priming on caraway germination and how early seedling performance can easily be adopted by producers.

A pot experiment was conducted to assess the effect of drought stress on growth and secondary compound accumulation of Ocimum species, in a semi-controlled greenhouse during the year 2020. The experiment was performed as a factorial that was based on a randomized complete design with three species of basil namely O. basilicum ‘Genovese’, O. x africanum, and O. americanum, and three levels of water supply (70, 50, and 30% soil water capacity-SWC) that were replicated twice. The results revealed that severe drought conditions (30% SWC) significantly lowered the relative water content and, as a consequence, plants were shorter, narrower in the canopy, and produced smaller leaves which, in turn, resulted in a 50% fresh and dry herb yield loss. Furthermore, severe drought stress negatively affected the essential oil content (except O. x africanum where no change was seen), essential oil yield, and the antioxidant capacity. However, slight enhancements of glandular hair density were observed in the drought treatment than in the control. Regardless of the soil water capacity variation, the major compound of the essential oil and total polyphenol content remained unchanged. Besides drought, morphological and chemical variations were also detected among the Ocimum species. Sweet basil cultivar Genovese produced the maximum biomass (344.7 g/plant) whereas O. x africanum accumulated higher essential oil (2.79%). The major compounds that were identified were linalool in O. basilicum; 1, 8-cineole, and camphor in O. x africanum; and O. americanum had more neral and geranial. In conclusion, a higher water supply is recommended for higher biomass and essential oil yield production in the tested basil species.

Salicylic acid (SA) and methyl jasmonate (MeJa) are prominent phytohormones that are involved in stress reactions. Both compounds may influence the biosynthesis of secondary compounds; however, scientific experiments in vivo are rare and contradictive. This paper reports on a study on the elicitation of volatiles and total phenolics (TPC) by MeJa and SA. The subjects were four Lamiaceae species studied in open field conditions in Budapest (Hungary). According to the results, both elicitors provoked specific responses in each plant species depending on the dosage applied and the parameter studied; 2 mM of SA stimulated essential oil (EO) accumulation in marjoram and peppermint, while in hyssop 0.1 mM was optimal. MeJa proved to be effective only in marjoram and in basil. In marjoram, cis-sabinene hydrate was decreased and in hyssop, isopinocamphone was increased by both dosages of SA. In peppermint, pulegone content was reduced by 2 mM SA, but no significant change of the major components of basil EO was detected. SA was successful in increasing TPC and antioxidant activity (AC) in three of the experimental species, but not in hyssop. In marjoram, only 0.1 mM induced TPC and eventually AC, while in peppermint and basil both dosages of SA were effective. Optimalisation of the treatments is suggested in further in vivo experiments.

The reactions of Majorana hortensis, Melissa officinalis, Mentha piperita and Thymus vulgaris were investigated in controlled conditions to compare their responses on drought stress concerning yield, essential oil (EO) content and composition. Biomass and essential oil concentration were significantly decreased in each species similarly, if they were grown at 40% level of soil water capacity (SWC) compared to the ones growing at 70% SWC. The largest changes were detected in lemon balm (4.47-fold difference in biomass, 2.78-fold difference in EO content) while the response of marjoram was the modest one (1.95-fold in biomass, 1.21-fold in EO content). We found species specific quantitative modifications in the EO composition. The ratio of terpinene-type components increased in the EO of both thyme and marjoram to the expense of their characteristic compounds thymol, carvacrol and sabinyl compounds, respectively. The composition of lemon balm and peppermint, however, did not show considerable changes.