Estimation of some growth characteristics of the Ajowan (Carum capticum L.) in response to salinity stress

IntroductionSalinity is a major abiotic stress limiting growth and productivity of plants in many areas of the world due to increasing use of poor quality of water for irrigation and soil salinization. Soil and water salinity in semi-arid regions such as Iran have been important threats for plant growth and agriculture. Distributed in semi-arid and arid parts of the world, ajwain, or sprague, (Carum capticum L.) is a medicinal and industrial plant of the Apiaceae family with white flowers and small brownish fruits. A good source of secondary metabolites, the seeds of ajowan have been used in food and pharmaceutical applications2. A variety of health properties was described for the ajowan seeds, which include antimicrobial, antioxidant, nematicidal, anti-inflammatory, carminative, and sedative effects.Materials and methodsWith the aim of estimation of some growth characteristics of the Ajowan in response to salinity stress, an experiment was conducted in a completely randomized design with 3 replications in a pot in the greenhouse of the National Salinity Research Center during 2020. Experimental treatment includes water salinity levels 0.4 (control), 3, 6, 9 and 12 dSm-1. At the beginning of planting, all the pots were watered with city water until establishment and germination and reaching the desired density. And then to avoid introducing sudden stress to the plant, salinity treatments were gradually increased during a period of 20 days after planting according to each treatment. After 8 months after planting in the stage after flowering, some quantitative characteristics of the plant were measured as follows: plant height, fresh and dry weight of shoots, root dry weight, lateral stem number, relative water content, ion leakage, potassium and sodium of shoots. Analysis of variance of the data was calculated using SAS Ver 9.2 statistical software, and mean comparison was performed using the LSD test at the 5% probability level.Results and discussionThe results showed that all investigated traits were affected by different levels of salinity. As by increasing the salinity from the control treatment (0.4 dS.m-1) to a salinity of 12 dSm-1 caused a decrease of 63% in the height of the plant, 58% in the shoot fresh weight, 42% in the shoot dry weight, 47% in the root dry weight, 13% in relative water content and 45% in potassium. Also, increasing salinity from control treatment 0.4 to 12 dSm-1 caused an increase in the amount of sodium and ion leakage by 46% and 11.5%, respectively. In many studies, reports indicate a significant effect of salinity on the reduction of the growth characteristics of Ajowan plants. It seems that in the present study, with the increase in salinity stress level, plant height decreased due to the harmful effects of salinity. Correlation results showed that the highest effective traits on dry weight of shoot dry weight included potassium and ion leakage. One of the reasons for the decrease in dry matter was the increase in ion leakage and the decrease in potassium content of the plant, and correlation and regression studies also indicated a high correlation between ion leakage and potassium content with plant dry matter.ConclusionThe results indicated that the growth traits and related to the yield of the Ajowan decreased significantly with the increase in irrigation water salinity. Also, salinity stress significantly decreased the relative water content and decreased the amount of potassium and the ratio of potassium to sodium and increased the ion leakage and sodium percentage of the plant. Correlation and regression studies also indicated a high correlation between ion leakage and potassium content with plant dry matter. The changes in plant dry matter yield between other salinity levels, 3, 6, and 9 were not significantly different from plants under the control treatment. In general, we can recommend ajwain plant as one of the promising salinity-tolerant medicinal plants for further studies.