Stimulative effect of chitosan with amino acid to enhance growth, essential oil, and some physiochemical characteristics of two Mentha cultivars

Background Mint plants (Mentha spp.) are a member of the Lamiaceae family and it has long been used in medicine. Its applications include carminative, anti-inflammatory, antispasmodic, antiemetic, diaphoretic, analgesic, stimulant, emmenagogue, and anticatarrhal. Adding chitosan to medicinal plants has a major role in the process of secondary metabolism, as its addition stimulates the production of chemical compounds or essential oils in the plant. Amino acids are one of the possible strategies for increasing agricultural productivity. They are organic nitrogen polymers that are used as the building blocks of proteins and enzymes. Objective This study aimed to determine how chitosan, in combination with or without the foliar application of amino acids, affected the growth and physiological traits of two cultivars of mint. Materials and methods Two pot trail investigation studies were carried out during the two consecutive seasons 2021 and 2022 under the natural conditions of the greenhouse of the National Research Center (NRC), Dokki, Giza, Egypt. To study the effect of two levels of chitosan (1.5 and 3.0 g/l with amino acid at rates of 50 and 100 mg/l) as foliar application on growth, essential oil, and some physiochemical characteristics of two Mentha (Mentha viridis and Mentha longifolia L.) cultivars. Results and conclusion The results show significant differences between two mint cultivars in the growth parameters of mint plants. Plants of M. viridis variety were characterized by the highest significant values of herb fresh weight, number of branches/plants, essential oil (%), flavonoid content, and protein %, while the M. longifolia variety was superior in plant height, herb dry weight, chlorophyll a, chlorophyll b, carotenoids, total pigments, indole acetic acid, phenol, carbohydrates %, free amino acids, flavonoid, and proline contents. Using chitosan as foliar treatments at different concentrations with or without amino acid significantly increased all studied traits. The interaction between two cultivars and foliar treatments of high rates of chitosan and amino acid gave the maximum significant increase of plant height, photosynthetic pigments and indole acetic acid, phenol, protein, free amino acid, and proline contents as well as antioxidant activities (DPPH%).