Drought and salinity stress in medicinal and aromatic plants: Physiological response, adaptive mechanism, management/amelioration strategies, and an opportunity for production of bioactive compounds

Drought and salinity stresses pose a constant threat to global agricultural crops and have been considered the major obstacles to increasing productivity. The most prominent effects of drought and saline stress on plants are stunted growth, degradation of chlorophyll, decrease in net photosynthesis, imbalances of ionic and osmotic homeostasis, and ultimately reduction in yield. To lighten the adverse effects of both stresses on the plants and to ensure higher productivity and quality, it is imperative to understand the agro-morphological, physiological, and biochemical responses of plants under drought and salinity conditions. This review highlights the influence of drought and salinity stresses on the agronomical and physiological aspects (chlorophyll, photosynthesis, stomatal conductance, transpiration rate, and nutrient uptake) of plants, particularly medicinal and aromatic plants (MAPs). The in-depth discussion also focuses on various adaptation mechanisms like morphological and anatomical changes, osmolytes accumulation, enzymatic and non-enzymatic defense, and biosynthesis of secondary metabolites. Additionally, the various agronomic and biotechnological strategies to reduce the severity of water and saline stresses are also critically discussed for the sustainable production of MAPs. The implementation of agronomic and biotechnological approaches will be helpful in minimizing the negative effects of water and salt stresses in MAPs, and exploration of these adverse conditions for the synthesis of bioactive natural compounds. We also lucidly examined past research addressing the effect of water and salinity stress on the productivity of MAPs. Finally, we figured out how agronomic and biotechnological strategies help to increase the production of MAPs under drought and salinity stress environments.