Morphological and phytochemical response of dill (Anethum graveolens L. to Natural zeolite under drought stress

Water deficit is one of the major limiting factors that influences the cultivation and production of agricultural crops in the world. Drought stress severely impairs plants growth and development through alterations in the physiological, morphological, biochemical, and molecular attributes (Cheng et al., 2018). Most of the world's farms are located in arid and semi-arid regions. In addition, drought conditions can be exacerbated by climate change and water scarcity. Therefore, it is important to find a way for increasing the adaptation potential of crops to water shortage (Asghari et al., 2020). Zeolite can act as water moderators and play a key role in plant growth and development under drought condition. The aim of this research was to investigate the effect of zeolite application on morphological traits and secondary metabolite biosynthesis of dill (Anethum graveolens L.) under drought stress.

This study was conducted as a factorial experiment in a completely randomized block design with three replications in the greenhouse. The experimental factors included irrigation regimes in 3 levels (40 %, 80 % and 100 % of filed capacity (FC), application of zeolite in 2 levels (0.0 and 2.5 g/ kg of soil) and plant ecotype (Naeen and Zavereh). Seeds of dill were obtained from Pakan Bazr Company, Isfahan, Iran. The seeds were cultured in pot containing sandy loam soil. When plants were fully established, drought treatment was started and continued until harvest. Then, we measured some morphological and biochemical attributes of dill plant. The obtained data were analyzed using analysis of variance (ANOVA) performed with SAS software. Duncan’s multiple range test was used to distinguish the differences in treatments.

The results showed that water deficit and zeolite application significantly affected morphological and biochemical properties of dill plant. Drought stress reduced plant height, leaf area, fresh ant dry weight of plant, number of umbrella per plant and 1000 grain weight but only amplified root length. Application of zeolite alleviated drought-related damages and promoted plant growth and development, which increased leaf area and the amount of grain per plant, and reduced root length and plant height. A similar effect of drought stress and zeolite treatment has reported in Dracocephalum moldavica (Gholizadeh et al., 2010). Our data demonstrated that mention attributes significantly influenced by the plant ecotype, and Naeen was more effective than Zavareh. The results illustrated that the severity of drought stress play a key role in the amount of phytochemical compounds of dill seeds. The highest amount of dill ether and alphaphellandrene was recorded under normal condition. While, the highest level of limonene was obtained in plants subjected to moderate drought stress. In addition, the severe water stress led to the highest accumulation of carvone and transdihydrocarvone in dill seeds. Zehtab Salmasi et al., (2016) reported that water shortage causes an increase in dill ether and limonene of dill plants.

Water deficit adversely affected normal growth and morphological properties of dill plants. The obtained results showed that dill plant could adapt to drought condition by raising its protective compounds and root length. Water stress significantly enhanced essential oil percentage of basil plant, leading to accumulation of dill ether, carvone, transdihydrocarvone and limonene in its seed. The exogenous usage of zeolite can successfully alleviate deleterious impacts of water shortage on dill plant by improving morphological characteristics and stimulating secondary metabolites production.