The Effect of Using Different Levels of Vermicompost on The Growth and Morphological and Physiological Characteristics of Medicinal-Ornamental Plant of Mullein (Verbascum thapsus) Under Drought Stress Conditions

The use of organic fertilizers is one of the appropriate ways to produce medicinal plants due to their proper impact on the various soil properties, maintaining environmental health and better plant growth. This study was conducted to investigate the impact of various vermicompost levels on the growth and the morphological and physiological properties of the medicinal-ornamental plant of the Mullein, under drought stress conditions. The research was carried out in the form of split plots in a complete blocks design with four replicates. Experimental treatments included the use of vermicompost organic fertilizer at three levels of zero, 4, and 8 kg/m2 (equivalent to zero, 4, and 8 tons per hectare) and drought stress at two levels of normal irrigation (no stress) and irrigation at 50% of soil field capacity (FC). The results showed that the use of vermicompost and drought stress improved the morphological and physiological traits of the medicinal plant of Mullein. The highest height of the stem, the stem flower, the number of leaves, the height of the flower, the dry weight of shoot, and the root length were obtained by the use of vermicompost at 4 and 8 kg/m2 levels. The use of vermicompost at the rate of 8 kg/m2 increased chlorophyll and anthocyanin, respectively, by 53.7 and 122% compared to control. It was observed that by applying vermicompost at the levels of 4 and 8 kg/m2, significant changes in the morphological and physiological traits of the Mullein plant occurred. On the other hand, the combination of vermicompost application and mild drought stress also caused positive changes in the plant traits. Therefore, mild drought stress, and also for improving the vegetative growth and reproductive efficiency of the medicinal-ornamental plant of the Mullein, the use of vermicompost at 4 kg/m2 (equivalent to 4 tons per hectare) are recommended.