Comparative physiological responses of english lavender cultivars to drought stress and abscisic acid treatments with implications for agricultural water management.

Global warming is one of the important environmental issues that has led to climate change and affected agriculture and water resources. Considering the negative impact of drought in limiting the yield of agricultural products, it is necessary to introduce management methods such as the use of suitable cultivars and growth regulators like abscisic acid (ABA). This research, by simultaneously studying the physiological parameters related to photosynthesis, water relations, and osmotic regulation in two varieties of English lavender (Hidcote, Munstead) under different drought and ABA treatments, fills the existing gap in understanding the mechanisms of adaptation, particularly the relationship between changes in photosynthetic gas exchange and osmotic regulation. This valuable medicinal plant addresses drought stress. In this research, the effect of different levels of drought stress (90-100%, 70-80%, 50-60%, and 30-40% field capacity) and ABA (0, 15, and 30 µM) on the physiological parameters of two lavender plants was investigated. Drought stress significantly reduced RWC in both cultivars, while the exogenous application of ABA helped reduce water loss. Hidcote showed better water retention (maximum RWC 85.95%) compared to Munstead (maximum RWC 73.49%). The photosynthesis rate of Hidcote decreased from 11.46 to 8.33 µmol m⁻² s⁻¹ with 30 µM ABA, and Munstead's rate decreased from 9.1 to 6.05 µmol m⁻² s⁻¹ with 30 µM ABA. The rate of transpiration also showed a similar decreasing trend. Water use efficiency (WUE) increased with decreasing field capacity (FC) and increasing ABA concentration. Munstead showed superior WUE compared to Hidcote across treatments. this study showed that proline content accumulation increases under stress, with Hidcote reaching a maximum of 5.07 µmol/g FW at D4A3 and Munstead a maximum of 4.3 µmol/g FW at D4A2. The conductivity of the mesophyll decreased under stress but showed numerical differences. In general, the evaluation of the two cultivars showed that the Hidcote cultivar has better water -holding capacity, a higher photosynthesis rate in optimal conditions, and a more sensitive response to stress. In contrast, the Munstead cultivar showed better water use efficiency, more stable performance under stress, and better adaptation to drought conditions. These findings help to understand the physiological mechanisms and plant water relations that affect water stress tolerance in lavender and, by analyzing the differences in cultivar responses to stress, provide new knowledge in the field of selection and improvement of drought -tolerant cultivars.