Effects of drought stress on yield and yield-related traits, antioxidant enzymes and essential oil content of some Cumin (Cuminum cyminum L.) ecotypes

Introduction Cumin (Cuminum cyminum L.) as an annual herbaceous plant belonging to the Apiaceae family, is one of the most important medicinal plants in Iran, which needs a lower irrigation to complete the growth stages. Therefore, cumin is one of the most valuable plants for cultivation in arid and semi-arid regions of the world, especially in drought conditions. Drought is one of the most important factors limiting the growth of plants around the world and the most common environmental stress. For this purpose, the present study was conducted to evaluate the key morphological and physiological parameters as well as the factors involved in oxidative stress and essential oil content in some ecotypes under drought stress and normal conditions. Materials and methods The experiment was arranged as factorial based on a completely randomized design with three replications and conducted in Saravan University's research greenhouse. Experimental factors included drought stress (stress and non-stress) and different ecotypes (eight ecotypes). The measured traits were plant height, number of secondary branches per plant, number of umbel per plant, number of umbellate per umbel, number of seeds per umbel, 1000-seed weight and seed yield per plant, chlorophyll a, b and carotenoid content, and activity of biochemical factors (catalase, superoxide dismutase, peroxidase, malondialdehyde) and also seed essence. Finally, analysis of variance and mean comparisons of the data were analyzed using SAS ver. 9.1 and R ver. 3.5.1 software. Results and discussion The results showed that drought stress reduced yield, yield components and photosynthetic pigments content. In general, Birjand ecotype had the highest grain yield per plant (1.37 g). The activity of antioxidant enzymes in this medicinal plant was found to be valuable in which drought stress increased the activity of antioxidant enzymes and malondialdehyde levels. Birjand ecotype had the highest percentage of seed essence (3.25%) among the studied ecotypes, though had no significant difference with the Isfahan ecotype (3.8%). In non-stress conditions, the amount of biochemical factors was low. Under drought stress, the amount of these factors and essence content were significantly increased in the studied ecotypes. Ecotype Yazd in drought stress conditions produced catalase and superoxide dismutase content more than other ecotypes. Regarding the Birjand ecotype, which was one of the top ecotypes in this experiment, although the antioxidant activity of catalase and superoxide dismutase was not the highest, the level of malondialdehyde, which is a sign of damage to the plant, was also not high, and it is likely that the other mechanisms help to consistent the yield. Sabzevar ecotype had the highest (83.5%) and Birjand ecotype had the lowest (52.99%) increase in essential oil under drought stress condition. Finally, according to the measured indexes, the tolerance of the ecotypes studied to drought stress was identified and Birjand ecotype was identified as superior ecotype. Conclusions In this study, the effect of drought stress on flowering stage on functional, physiological, biochemical and essential aspects of native sub-cluster ecotypes was studied. The results showed that there was a good variation among different ecotypes for different traits and drought tolerance. In the meanwhile, Birjand ecotype had a certain superiority in terms of drought tolerance, grain yield and essential oil content than other ecotypes studied.