Effects of some essential oils on morphological, physiological and biochemical properties and grain yield and quality of sunflower in water stress conditions

In this thesis study, it was aimed to determine the effects of thyme (Thymus vulgaris L.), clove (Syzygium aromaticum L.), rosemary (Rosmarinus officinalis L.), juniper (Juniperus communis L.) essential oils and Messenger Gold applications on sunflower plants under water stress conditions on morphological, physiological and biochemical characteristics, and their effects on plant development and grain yield in field conditions and their roles in tolerance to water stress. The study was carried out in field conditions in 2020 and 2021, and in the plant growth chamber in 2021. Granit and Gibraltar sunflower varieties were grown in the plant growth chamber at three drought levels (S1, S2 and S3 water subjects; when 40-50%, 60-70% and 75-85% of the field capacity was consumed), and in irrigated and dry conditions in field conditions. On sunflower plants, essential oils were applied at 500 and 1000 ppm doses, and plant activator Messenger Gold was applied at 6 g/da dose to the upper parts of the plant with a pulverizer three times at 15-day intervals starting from the 6-8 leaf period of the plants. Although it varied according to water stress levels in the plant growth chamber, the applications increased plant morphological and physiological characteristics. It was determined that the applications significantly increased the proportional water content, chlorophyll and carotenoid amounts in water stress; and reduced membrane damage, proline, MDA and H2O2 amounts. In field conditions, applications showed a reducing effect on antioxidant enzyme activities (SOD, CAT, APX and GR) under stress conditions, especially in Clove 1000 ppm, Juniper 500 ppm and Thyme 500 ppm applications, which achieved high yield increases. In field conditions, essential oils increased the head diameter, thousand grain weight and full grain ratio affecting yield; It provided a 29% increase in yield compared to the control in wet conditions and approximately 20% increase in yield in dry conditions. This study concluded that essential oils can be used effectively in providing tolerance to water stress.