ghader rostami; Leila Samiei; Sadrollah Ramezani
Abstract
IntroductionPeppermint (Mentha piperita) is an important medicinal plant in the Lamiacea family and its essential oil is used in food, medicine, cosmetics, baking, gum making, soft ...
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IntroductionPeppermint (Mentha piperita) is an important medicinal plant in the Lamiacea family and its essential oil is used in food, medicine, cosmetics, baking, gum making, soft drinks, and additive industries. This plant faces abiotic stresses including drought during the growth period. Considering that ecotypes have developed a series of adaptions against harsh environments, peppermint is one of the important genetic resources for developing products in regions with water shortage, Therefore because of the dominance of arid and semi-arid conditions in most parts of Iran, this study was conducted to evaluate effects of drought stress on growth and biochemical characteristics and select the best ecotypes of peppermint. Materials and MethodsTo evaluate the drought resistance of various ecotypes of peppermint, a pot experiment as a factorial based on a completely random design with three replicates was conducted in the research greenhouse of the Faculty of Agriculture at Ferdowsi University of Mashhad during the 2022 growing season. The first factor was drought stress in two levels including 70 (moderate stress) and 50 (severe stress) field capacity, and the second factor was six peppermint ecotypes (Mazandaran, Mahan (Kerman), Tabas, Sarakhs, Khash, and Qazvin) collected from different regions of Iran. Plants identification was done at Ferdowsi University of Mashhad, Research Institute of Plant Sciences.The drought was posed for two months and morphological and biochemical factors were measured in the flowering stage. The studied traits include the number of branches, length and width of leaves, diameter of stem, length of inflorescence, number of inflorescences, dry weight of leaf and stem, contents of photosynthetic pigments (chlorophyll a, b, and carotenoid), total phenol, total flavonoid, antioxidant activity, relative water content (RWC) and ion leakage. Results and DiscussionThe results showed that the interaction effect of drought and ecotype was significant on all traits. With increasing drought stress, plant height, the number of branches, length and width of leaves, the number of influences, length of influence, diameter of the stem, dry weight of leaf and stem, the content of photosynthetic pigments (chlorophyll a, b, and total) and relative water content of leaves were decreased in different ecotypes, so that the highest values for these parameters were in moderate stress (70% FC), and the lowest were in severe stress (50% FC). It is possible that the severe decrease in soil moisture in 50% of the field capacity has caused a decrease in the availability of water and minerals for the peppermint ecotypes and ultimately caused a decrease in growth indicators. With increasing drought stress (50% of field capacity), antioxidant activity (94.46%, 94%), carotenoid content (2.83, 2.80 mg/g FW), total phenolic content (8.55, 10.58 mg/g FW), and total flavonoid content (13.17, 12.27 mg/g FW) increased in the Mazandaran and Sarakhs ecotypes, respectively. Compared to mild stress (70% FC), antioxidant activity increased by 32% and 39.67% in the Mazandaran and Sarakhs ecotypes, respectively; carotenoid content increased by 138% and 131%; total phenolic content rose by 30.53% and 29.65%; and total flavonoid content grew by 38.34% and 33.36%. Meanwhile, cluster analysis and biplot grouped the resistance ecotypes (Sarakhs and Mazandaran) in the same cluster and the remaining ecotypes (Mazandaran, Mahan (Kerman), Tabas, Sarakhs, Khash, and Qazvin) in another cluster as sensitive ecotypes. It is believed that Fern and Mazandaran ecotypes have activated the non-enzymatic pathway to accumulate compounds such as total phenol, total flavonoid and increase antioxidant capacity to moderate the destructive effects of oxidative stress and increase the tolerance of this plant to drought stress. Also, the grouping of different peppermint ecotypes did not fully correspond to their geographical distribution, which indicates that apart from the climatic factor related to the geographical origin, there are other reasons such as the exchange of genetic materials, importing genetic materials and Genetic erosion is effective in existing diversity.ConclusionThe result of drought stress on peppermint ecotypes in two moderate (70% FC) and severe (50% FC) stresses indicated that Sarakhs and Mazandaran ecotypes have the highest adaptability under drought stress through increasing phenolic compounds, keeping humidity and the lowest damage from ion leakage compared to other ecotypes. Therefore, Sarakhs and Mazandaran ecotypes could be recommended as drought-resistance ecotypes compared to other ecotypes and proposed for further study.
