Climate change and its undeniable consequences such as drought stress are serious problems for plants. Therefore, the development of new management approaches, such as the cultivation of drought-resistant genotypes of medicinal and industrial plant species by determining the most suitable irrigation regime and the use of compounds such as salicylic acid to increase the bio-active components of the plant is necessary. Through inducing the formation of secondary metabolites, we are able to reduce the adverse effects of drought stress and improve the sustainable production of effective ingredients in plants. Therefore, referring back to the to the forgotten medical-industrial plant “the indigo (Indigofera tinctoria)”, by recalling its medicinal uses and especially the natural production of blue color source to the agricultural field of the country, can be a suitable option, mainly for cultivation in areas with limited water supply. Indeed, it is a strategy to reduce pollutants related to the paint industrial productions. The aim of this research is to investigate the effects of drought stress and salicylic acid on the morphological characteristics, pigment content in the stem and leaves of the indigo plant and also determining the optimal conditions for the extraction of pigment. Effect of three different levels of irrigation: 50% depletion of available soil water from the soil (control irrigation), 70% depletion of available soil water (mild stress) and 85% depletion of available soil water from the soil (severe stress) as well as, effects of three different levels of salicylic acid (in the concentrations of 0.0, 0.5 and 1.0 mM) on two genotypes of indigo plant (Yazd and Kerman) were eva‎luated using a factorial split based on a completely randomized blocks design with three replications. The results showed that with the increase of drought stress, plant height, number of sub-branches, canopy diameter, number of leaves, weight of dried leaves and dried stems are decreased, and also the highest level of the aforementioned traits was related to the irrigation level of 50% soil moisture discharge while the lowest values were related to the irrigation level of 85% soil moisture discharge. Salicylic acid at 1 mM level improved the plant height while the best value of salicylic acid for increasing the weight of dried leaves and stems is the 0.5 mM level, but effects of salicylic acid on the traits of number of sub-branches, canopy diameter and number of leaves was not significant. By increasing the dryness levels, the amount of leaf pigment is increased, while the amount of stem pigment decreases. In both Yazd and Kerman varieties, increasing the concentration of salicylic acid from 0 to 0.5 and 1 mM causes an increase in the amount of leaf pigment, and the highest amount of leaf pigment in Kerman variety was obtained under the conditions of using 1 mM salicylic acid, while the lowest amount of leaf pigment was obtained without using salicylic acid in Yazd variety. The highest amount of stem pigment was obtained under the humidity condition of 50% soil moisture depletion and no use of salicylic acid, while the lowest amount of stem pigment was obtained under the humidity condition of 70% soil moisture depletion and the use of 1 mM salicylic acid in both populations. These results clearly indicate that the external application of salicylic acid increases leaf pigmentation, but it has a decreasing effect on stem pigmentation. Finally, according to the obtained results, it can be concluded that, the drought stress causes a decrease in all the investigated morphological traits, and spraying salicylic acid improves the height and dry weight of leaves and stems under moisture stress conditions. This plant growth regulator especially increases the pigment in the leaves of the indigo plant under control conditions and different levels of drought stress.

حسن كريم مجني، جمشيد رزمجو

حميد ميرركني بنادكي، حسين عجمين

حميدرضا عشقي زاده، مريم حقيقي