Drought stress is an important environmental limiting factor that affects the physiological and biochemical response of medicinal plants and changes the process of plant secondary metabolism. In the present study, a pot experiment was conducted to evaluate the morphological, physiological, and phytochemical response of Mexican marigold (Tagetes minuta L.) to drought stress (100%, 75%, 50%, and 25% Field Capacity) with three replications based on a completely randomized design. After prolonged water deficit, growth responses, oxidative stress indicators, and phytochemical variations in unstressed and stressed plants were recorded. Decreasing of water availability had a negative effect on T. minuta growth. The photosynthesis pigments and relative water content of stressed plants were decreased, but the accumulation of malondialdehyde, osmolyte compounds, and total phenol content were increased with increasing water limitation. The activity of catalase, guaiacol peroxidase, ascorbate peroxidase, and polyphenol oxidase in stressed T. minuta plants was also increased in response to drought stress. Although water limitation did not show a considerable effect on the essential oil content of T. minuta, the essential oil composition was significantly influenced by drought stress and dihydrotagetone was the main constituent in all essential oil samples. Drought stress changed the relative proportions of essential oil constituents and induced synthesis of new constituents included 1,8-cineole and germacrene D. Taken together, our findings suggested that the 75% FC treatment can be introduced as an acceptable drought level that T. minuta showed sufficient resistance.

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