Exploring the Impact of Drought Stress on the Yield and Yield Components of Cumin (Cuminum cyminum L.) Ecotypes

IntroductionDrought stress poses a significant challenge to cumin production in Iran, particularly during the flowering and seed-setting stages. Cumin is a valuable crop with numerous medicinal properties and applications in various industries. Despite its short growing season, the economic importance of cumin makes it imperative to find ways to mitigate the effects of drought stress on seed yield. Addressing the negative effects of drought stress is crucial for improving cumin seed yield. One effective strategy is to identify drought-resistant cumin cultivars. By selecting cultivars that are more resilient to drought conditions, farmers can enhance their chances of achieving higher yields, even in challenging environments. Materials and Methods This two-year study (2020-2021) aimed to assess the drought tolerance of 15 cumin ecotypes under field conditions in Karaj, Iran. The experimental design was a randomized complete block design with three replications. The ecotypes evaluated were: Tabriz, Torbat Jam 8, Afghani, Khorasan-Birjand, Yazd 7, Yazd 8, Torbat Jam 9, Khorasan Razavi 8, Pakistan, Isfahan, Hindi, Khorasan Razavi 12, Isfahan 13, Sabzevar, Torbat Heydarieh. Two treatments were applied: full irrigation and drought stress. Irrigation under full irrigation was carried out every 10 days according to soil and weather conditions, while irrigation was withheld from 50% flowering to the end of the growth period under drought stress.Results and Discussion The results of this study showed that drought stress reduced the yield and yield components of cumin ecotypes but increased the essential oil content. The highest seed yield of 102.78 g m-2 was achieved by the ecotype Turbat Jam 8 under full irrigation conditions, which was statistically similar to the ecotypes Afghani, Khorasan-Birjand, Yazd 7, Turbat Jam 9, and Sabzevar under normal irrigation conditions. The lowest seed yield of 65.8 g m-2 was recorded for the ecotype Khorasan Razavi 12. These results demonstrate the differential tolerance of cumin ecotypes to drought stress and highlight the potential of Turbat Jam 8 as a drought-tolerant ecotype. The Afghani ecotype proved to be drought-resistant, showing consistent grain yield under both normal irrigation and drought stress. Conversely, the Khorasan Razavi 12 ecotype was vulnerable to drought stress, exhibiting reduced biological and grain yields under these conditions. Notably, a strong positive correlation (0.973) was observed between essential oil content and seed yield, indicating that breeding for high essential oil content could also improve drought resistance and yield. In addition to the strong correlation between essential oil content and seed yield, other correlations were observed. The amount of essential oil was positively correlated with the harvest index (0.787) and the weight of one thousand seeds (0.721). Seed yield also showed positive and significant correlations with the number of umbrellas per plant (0.396), harvest index (0.287), and the number of seeds per umbrella (0.232). No other traits showed significant correlations. Biological performance had positive and significant correlations with plant height, number of branches per plant, number of umbels per plant, number of umbels per umbel, and number of seeds per umbel. According to the result of cluster analysis based on Ward's method, the ecotypes were divided into three groups. The highest number of ecotypes was in the third group (7 ecotypes) and the second group (6 ecotypes). The Afghani ecotype formed the first group alone. According to the type of ecotypes placed in a cluster, it can be said that the ecotypes in a cluster were very similar in terms of morphological and molecular characteristics, and the Afghani ecotype was different from other ecotypes.Conclusion     Drought stress and ecotype interactions had a significant impact on plant height, biological yield, and grain yield. The variation in ecotype responses to drought stress may be attributed to genetic differences. The Afghani ecotype demonstrated strong resistance to drought, showing no significant reduction in grain yield under both normal irrigation and drought stress conditions while also achieving the highest essential oil content. In contrast, the Khorasan Razavi 12 ecotype was highly sensitive to drought stress, exhibiting markedly lower biological and grain yields compared to other ecotypes.