The Effect of Irrigation Intervals and Anti- transpiration Compounds on Morphological Traits, Physiological Traits, and Irrigation Water Efficiency Index in the Nigella sativa L.

Nigella sativa L. is one of the herbs that has a variety of uses and has been used in Iran’s traditional medicine since old times. Today this plant is considered as one of the most important kinds of medicine. Almost all the metabolic activities of plant cells, including the construction of active ingredients in medicinal plants, depend on lack of absorbable water by plants can lead to the morphological, physiological and biochemical changes, including decrease of cell swelling and growth and thus reduction of leaf area and plant height, stomatal closure and photosynthesis restriction, increase of soluble compounds for regulating the osmotic pressure, reduction of nutrient absorption and ultimately reduction of crop production. The use of anti-transpiration compounds is considered as a promising tool for the regulation of transpiration in respect of water conservation at an optimal level, where the strategies such as the use of anti-transpiration compounds have the potential for transpiration regulation. The aim of the present study is to improve the yield and yield components of medicinal plant N. sativa by anti-transpiration compounds under drought stress conditions.

The research was done using a split plot experiment on a randomized complete block design with three replications. The irrigation intervals (8 and 16 days) in main plots and anti-transpiration compounds of chitosan (0.25, 0.5 and 1 %), Plantago psyllium mucilage (0.5, 1 and 1.5 %) and arabic gum (0.25, 0.5 and 0.75 %) were put in subplots with three replications. Also, the distance between the main plots in each block and distance between the two blocks were assigned as 100 cm and 200 cm, respectively; so that the moisture content of a plot had no effect on the adjacent plots. Planting date was April 16 and planting was performed by hand in 0.5cm-deep furrows. Anti-transpiration compounds were sprayed simultaneously with applying drought stress till the flowering stage once a week at sunset. Plant height, leaf area index, irrigation water efficiency index, leaf temperature and stomatal conductance were measured.

The results showed that there were significant differences between treatments in all studied traits. The best rate of the measured traits was observed at 8-day irrigation interval and chitosan treatment. Providing plant favorite conditions such as reducing plant temperature, increasing morphological traits comparing to rainfed at 16-day irrigation interval. Applying arabic gum did not improve growth but acted as a growth inhibitor. Anti-transpiration compounds led to significant changes in all the studied traits compared to the control, indicating the effectiveness of these natural compounds. Chitosan stimulating abscisic acid synthesis in the treated plant would result in stomatal closure, reduction of stomatal conductance, transpiration rate and water content. It also pointed out that the anti-transpiration effect of chitosan was because of its stimulatory effect in increasing abscisic acid concentration in the treated leaves of bean plant. As the above compounds are natural and biodegradable, as well as safer and less expensive than other chemical anti-transpiration compounds, they can serve as a good alternative to the chemical compounds. Cognition and expertise in water relations of plant and drought stress tolerance is considered as the main program in agriculture and the ability to withstand this stress is of great economic importance.

The important processes, including nutrition, photosynthes is, stomatal opening and closure and growth are all influenced by water. In this study, it was observed canopy temperature and stomatal conductance would increase at 16-day irrigation interval, where the increase is considered as a drought tolerance mechanism. Also, the anti-transpiration compounds led to significant changes in terms of all the studied traits compared to the control, indicating the effectiveness of theses natural compounds. Providing the appropriate conditions, 1% chitosan treatment can enhance the yield under drought stress. Spraying by arabic gum did not improve the growth conditions. According to this experiment, 1% chitosan treatment and 1.5% Plantago psyllium mucilage is considered the most appropriate strategy to enhance the yield of Nigella sativa under drought stress.