Establishing stress conditions and physiological parameters for studying drought and broomrape stress responses in sunflower (Helianthus annuus L.)

With the increasing frequency and intensity of droughts and the threat of new pathogen populations due to climate change, understanding plant responses to stresses is crucial. This work studies the physiological effects of drought stress in sunflowers (Helianthus annuus L.) to set repeatable water stress procedures which mimic field stress conditions, for investigating stress response at transcriptomic and epigenomic level. Two sunflower lines were tested: ABOR6 (drought-resistant) and DFAB1 (drought-susceptible) grown under controlled greenhouse conditions. Also, the reaction of the drought resistant sunflower line to the parasitic plant Orobanche cumana was assessed in an independent experiment. In the case of O. cumana, the reaction of the line to be assessed was compared with the one of a susceptible confectionary control by means of inoculation by sowing in parasite seed-infested soil. A drought stress treatment with recovery was applied, followed by measurement and comparison of physiological parameters, such as stomatal conductance, chlorophyll content, transpiration rate, nitrogen balance index. Our results showed that the chosen physiological parameters can be used to monitor the sunflower plants response to drought stress and determine the time necessary for a complete recovery from it. The findings can contribute to a deeper understanding of sunflower physiology under water stress and potentially guide the development and breeding of drought-resistant sunflower cultivars in the face of a changing climate.