Exploring the Ecological Preferences and Essential Oil Variability in Wild-Growing Populations of the Endangered Local Greek Endemic Thymus holosericeus (Lamiaceae)

GC-MS analysis, phytochemical composition of Hertia cheirifolia L. essential oil with pharmacological assessments: antioxidant, antibacterial, and antifungal activities

The genus Hertia, which belongs to the Asteraceae family, is a flowering genus with 12 species found in Africa, North and South. Among the species present in Algeria, Hertia cheirifolia L. is distributed in the eastern regions of Algeria. The aim of this study is to evaluate its phytochemical composition with following pharmacological assessments: the antioxidant, antibacterial, and antifungal activities of Hertia cheirifolia L. essential oil (EO). GC-MS analysis was used to analyze the chemical constituents of H. cheirifolia essential oil. The antioxidant capacity was assessed using DPPH, FRAP, and H2O2 tests. The EO was also tested for its ability to inhibit six strains of microorganisms, including two Gram (+) and four Gram (-) strains. The antifungal activity was tested by analyzing the effect of the EO on the mycelial growth of Fusarium oxysporum f.sp. lycopersici (FOL) fungi. Results showed that primary volatile components were α-pinene (32.59%), 2-(1-cyclopent-1-enyl-1-methylethyl) cyclopentanone (14.62%), (-)-germacrene D (11.37%), and bakkenolide A (9.57%). H. cheirifolia EO showed inhibitory effects against DPPH, H2O2, and FRAP (IC50 = 0.34 ± 0.1, 0.053 ± 0.1, and 0.047 ± 0.01 mg mL-1, respectively). The EO also exhibited moderate antibacterial effects against Staphylococcus aureus ATCC 25923 (S. aureus), Streptococcus pneumoniae ATCC 49619 (S. pneumoniae), and Enterobacter aerogenes ATCC 13048 (E. aerogenes), as well as significant antioxidant potential and varied antifungal activity based on dosage and fungal strain. To our knowledge, no previous research has examined the antifungal capacity of H. cheirifolia oil and oil-mycelial development of the FOL relationship. To fully explore the benefits of H. cheirifolia EO, more in vivo research is necessary, along with more testing on other bacterial and fungal strains.

Exploring Chemical Variability in the Essential Oils of the Thymus Genus

Thyme remains an indispensable herb today, finding its place in gastronomy, medicine, cosmetics, and gardens worldwide. It is highly valued in herbal remedies and pharmaceutical formulations for its antibacterial, antifungal, and antioxidant properties derived from the richness of its essential oil, which comprises various volatile components. However, climate change poses a significant challenge today, potentially affecting the quality of thyme, particularly the extracted essential oil, along with other factors such as biotic influences and the plant's geographical distribution. Consequently, complex diversity in essential oil composition was observed, also influenced by genetic diversity within the same species, resulting in distinct chemotypes. Other factors contributing to this chemodiversity include the chosen agrotechnology and processing methods of thyme, the extraction of the essential oil, and storage conditions. In this review, we provide the latest findings on the factors contributing to the chemovariability of thyme essential oil.

Antibacterial effect of essential oils and their components against Xanthomonas arboricola pv. pruni revealed by microdilution and direct bioautographic assays

Bacterial spot of stone fruits caused by Xanthomonas arboricola pv. pruni (Xap) is one of the most significant diseases of several Prunus species. Disease outbreaks can result in severe economic losses while the control options are limited. Antibacterial efficacy of essential oils (EOs) of thyme, cinnamon, clove, rosemary, tea tree, eucalyptus, lemon grass, citronella grass, and lemon balm was assessed against two Hungarian Xap isolates. The minimal inhibitory concentration (MIC) was determined by broth microdilution assay and for the identification of active EOs' components a newly introduced high-performance thin-layer chromatography (HPTLC)-Xap (direct bioautography) method combined with solid-phase microextraction-gas chromatography/mass spectrometry (SPME-GC/MS) was applied. All EOs inhibited both bacterium isolates, but cinnamon proved to be the most effective EO with MIC values of 31.25 µg/mL and 62.5 µg/mL, respectively. Compounds in the antibacterial HPTLC zones were identified as thymol in thyme, trans-cinnamaldehyde in cinnamon, eugenol in clove, borneol in rosemary, terpinen-4-ol in tea tree, citral (neral and geranial) in lemon grass and lemon balm, and citronellal and nerol in citronella grass. Regarding active compounds, thymol had the highest efficiency with a MIC value of 50 µg/mL. Antibacterial effects of EOs have already been proven for several Xanthomonas species, but to our knowledge, the studied EOs, except for lemon grass and eucalyptus, were tested for the first time against Xap. Furthermore, in case of Xap, this is the first report demonstrating that direct bioautography is a fast and suitable method for screening anti-Xap components of complex matrices, like EOs.

Effect of Temperature on Breaking of Morphophysiological Dormancy and Seed Germination Leading to Bulblet Production in Two Endemic Tulip Species from Greece

Due to botanical tulips' economic interest coupled with limited information regarding their seed germination, we investigated the effect of temperature on dormancy release and germination in two endangered local endemic tulip species of Greece (Tulipa hageri Heldr., T. orphanidea Heldr.). Their germination responses at five constant temperatures (5, 10, 15, 20, and 25 °C) were evaluated in growth chambers, while the type of seed dormancy and the temperature effect on its release were determined based on open-sourced, R-derived species-specific ecological profiles illustrating abiotic conditions of their wild habitats. The results indicated a range-specific temperature dependence in seed germination for both studied species with seed germination observed only in very low temperatures (5-10 °C). The seeds of both species after dispersal had an underdeveloped embryo. The existence of a complex morphophysiological seed dormancy was confirmed in both species by the significant embryo development only at 5 and 10 °C (almost doubled after 30 days) coupled with observed delay in germination only at low temperatures. Furthermore, to facilitate their cultivation and ex situ conservation, the germinated seeds were planted in pots to develop bulblets in greenhouse conditions resulting in bigger T. orphanidea bulblets compared to T. hageri.

Influence of Temperature on Seed Germination of Five Wild-Growing Tulipa Species of Greece Associated with Their Ecological Profiles: Implications for Conservation and Cultivation

Although tulips are famous worldwide as ornamental plants, the knowledge about the seed germination of wild-growing species remains limited. The aim of the present study was to investigate the effect of temperature on seed germination of the local, wild-growing Greek endemics Tulipa bakeri and T. goulimyi and the sub-Balkan endemic T. undulatifolia, which are threatened with extinction, as well as the Mediterranean T. australis and the Asiatic T. clusiana naturalized on Chios Island (Greece). The germination responses at five constant temperatures (5, 10, 15, 20, and 25 °C) were assessed for all studied species in growth chambers under a 12:12 light-dark photoperiod. The ecological profile for each species was developed in R using open-source bioclimatic data; this was built to illustrate the abiotic environmental conditions of their wild habitats, to facilitate the examination of temperature effects on seed germination, and to facilitate their cultivation in artificial environments. The results indicated that the seed germination requirements of the studied species had a range-specific temperature dependence, reflecting their natural adaptation to local ecological conditions. Seed germination of T. bakeri, T. australis, and T. clusiana was observed only in a narrow range of very low temperatures (5-10 °C), whereas germination of T. undulatifolia and T. goulimyi occurred at temperatures between 5 and 15 °C. A temperature increase to 20 or 25 °C resulted in the absence of seed germination for all five Greek tulip species. The germinated seeds were planted in pots and bulblets were developed under greenhouse conditions. Seeds and bulblets constitute valuable genetic materials for the cultivation and ex situ conservation of these five Greek tulip species, three of which are threatened with extinction.