Phytochemical and morpho-physiological traits of mullein as a new medicinal crop under different planting pattern and soil moisture conditions

Mullein (Verbascum songaricum Schrenk.) is the biggest plant species belonging to the Scrophulariaceae family. The aerial parts of V. songaricum, especially leaves and flowers are used as herbal medicine by indigenous peoples of some regions of Iran. The effects of two planting patterns (square and rectangular) and different irrigation regimes, including irrigation in 90-85 % field capacity (F.C.) or control (I-1), irrigation in 60 % F.C. (I-2), irrigation in 45 % F.C. (I-3), and irrigation in 30 % F.C. (I-4) on some phenolic compositions, Malondialdehyde (MDA), catalase enzyme (CAT), proline, and growth parameters of V. songaricum as a new medicinal crop have been investigated. Field experiment was done two consecutive years (2016-17) in semi-arid climate, Southwestern Iran. Total phenolic contents of the ethanol extract from the leaves (2016 and 2017) and flowers (2017) determined by Folin-Ciocalteu assay and phenolic acids and flavonoid compositions of the flowers separated and quantified each component by high-performance liquid chromatography (HPLC). Results indicated that the planting patterns had not significant effects on biochemical and phytochemical features, however, the highest values of shoot dry weight and stem height were obtained from the plants cultivated in the rectangular pattern, and also the maximum dry weight of flowers was achievement from the mullein cultivated in the square pattern. Reduced irrigation significantly increased the contents of MDA, CAT, proline, and secondary metabolites such as total phenolic, phenolic acid (gallic acid), and flavonol quercetin, whereas, photosynthesis pigments and growth parameters (chlorophyll a, chlorophyll b, total chlorophyll contents, canopy diameter, plant height, and dry herbal weight) significantly decreased under deficit irrigation. In conclusion, reduced irrigation under the rectangular pattern significantly increased the amounts of total phenolic and flavonoids in the extracts from the leaves and flowers. Finally, the results of this study can be used in agricultural systems in order to growth, development and increase the quantity and quality yields of V. songaricum under reduced irrigation.