Essential oils isolated by using hydrodistillation from the aerial parts of Thymus algeriensis and Thymus capitatus Hoff. et Link. from different locations of Tunisia (Kef, Takelsa, Zaghouan, Fahs and Toukeber) were characterised. The chemical composition was analysed by using gas chromatography/mass spectrometry, the major component of T. capitatus from Kef and T. algeriensis was thymol while carvacrol was the main component of T. capitatus from Zaghouan, Fahs and Toukeber. The antifungal activity of the oils and some pure components was assessed by the in vitro assay against several fungi and oomycetes. T. capitatus (chemotype carvacrol) exhibited the strongest antifungal activity followed by T. capitatus (chemotype thymol) and T. algeriensis, indicating that carvacrol might have a stronger antifungal activity than thymol.

Coating seeds with bio-control agents is a potentially effective approach to reduce the usage of pesticides and fertilizers applied and protect the natural environment. This study evaluated the effect of seed coating with Meyerozyma guilliermondii, strain INAT (MT731365), on seed germination, plant growth and photosynthesis, and plant resistance against Fusarium culmorum, in durum wheat under controlled conditions. Compared to control plants, seed coating with M. guilliermondii promoted the wheat growth (shoot and roots length and biomass), and photosynthesis and transpiration traits (chlorophyll, ɸPSII, rates of photosynthesis and transpiration, etc.) together with higher nitrogen balance index (NBI) and lower flavonols and anthocyanins. At 21 days post infection with Fusarium, M. guilliermondii was found to reduce the disease incidence and the severity, with reduction rates reaching up to 31.2% and 30.4%, respectively, as well as to alleviate the disease damaging impact on photosynthesis and plant growth. This was associated with lower ABA, flavonols and anthocyanins, compared to infected control. A pivotal function of M. guilliermondii as an antagonist of F. culmorum and a growth promoter is discussed.

Coating seeds with biostimulants is among the promising approaches in crop production to increase crop tolerance to drought stress. In this study, we evaluated the potential of coating durum wheat seeds of the cultivar ‘Karim’ with thyme essential oil on enhancing seed germination and seedling growth, and on plant growth promotion and induction of drought resistance. Coated seeds were pre-germinated, grown in hydroponics, and grown in pots under controlled well-watered and progressive water/nutrient stress conditions. Seed coating with thyme oil increased germination rate and enhanced seedling growth development in hydroponics. In the pot experiment, thyme oil increased, when well watered, root and shoot development, chlorophyll, nitrogen balance index (NBI), abscisic acid (ABA), anthocyanins and flavonoids in leaves, decreased nitrogen isotope composition (δ¹⁵N) and increased carbon isotope composition (δ¹³C) of shoots. Increasing water/nutrient stress in control plants induced higher accumulation of ABA and anthocyanins coupled with a transient decrease in chlorophyll and NBI, a decrease in shoot and root development, the Normalized Difference Vegetation Index (NDVI), shoot C content, δ¹⁵N, and an increase in δ¹³C, revealing the avoidance strategy adopted by the cultivar. Thyme oil had the potential to enhance the avoidance strategy by inducing roots elongation, reducing the loss of shoot and roots dry matter and chlorophyll, maintaining balanced NBI, an decreasing anthocyanins, flavonoids, and δ¹³C via maintaining lower ABA-mediated-stomatal closure. Thyme oil increased shoot N content and δ¹⁵N indicating preferential uptake of the ¹⁵N enriched NH₄⁺. Coating seeds with thyme oil is suggested as a promising alternative approach to improve plant’s water and nutrient status and to enhance drought resistance.