Journal of Crop Breeding

Extended Abstract
Background: Medicinal plants are one of the important and valuable plant genetic resources in Iran, which can be considered and used in planting patterns in areas with environmental stresses and low-input agricultural systems due to their low water consumption and tolerance to environmental stresses under the current conditions. Unfortunately, due to climatic limitations (drought and salinity) and the effects of climate change, excessive harvesting of these reserves, and the increasing demand for medicinal plants in the world to meet the needs of various sectors (food, pharmaceutical, industrial, and cosmetic industries), these plants have been subjected to genetic erosion, which has caused concern among ecologists. Therefore, it is necessary to protect them in their natural habitats and to consider their cultivation and breeding based on scientific principles in agricultural fields. Black cumin (Nigella sativa L.) is an annual, self-pollinating plant native to semi-arid regions and is very important in terms of its oil and compounds. It is native to West Asia and is reported to have originated in the Middle East and the Indian subcontinent. Black cumin is a long-day plant and is usually planted in March. This plant is used in the treatment of depression, kidney failure, diabetes, stomach diseases, headaches, and toothaches, and has antibiotic, immune system stimulation, antimicrobial, anticancer, gum strengthening, and lactation effects. Black cumin is one of the valuable plant genetic resources in Iran, possessing high genetic diversity. This diversity among local landraces of black cumin can serve as a valuable source for selecting superior populations in breeding programs aimed at improving quantitative and qualitative traits, such as seed and oil yield. The wide geographical distribution of this plant across various regions of Iran—including Golestan, Isfahan, Yazd, Chaharmahal, and Bakhtiari, Fars, Hamedan, Khuzestan, Khorasan, Baluchistan, Tehran, and Arak—reflects its long history of domestication and adaptation to diverse environments. Therefore, this study was conducted to evaluate the genetic samples of black cumin conserved in the National Plant Gene Bank of Iran to identify desirable genotypes based on agronomic traits and seed yield.
Methods: To evaluate the genetic samples of black cumin conserved in the National Plant Gene Bank of Iran (36 accessions obtained from the Seed and Plant Improvement Institute, Karaj), an experiment was conducted during the 2021–2022 cropping season at the Gorgan Agricultural Research Station, Golestan Province, Iran. Each ecotype was planted in four lines of 3 m long and 30 cm spacing between lines. Pre-planting agricultural operations included plowing, spreading fertilizer, leveling, and planting. The required fertilizer was added to the soil based on soil tests. Phosphorus fertilizer from triple superphosphate was added to the soil when sowing seeds. Urea fertilizer was added to the soil in two stages (at the eight-leaf stage and at the stem stage). Planting was done by labor. The experiment followed a randomized complete block design (RCBD) with three replications. The studied traits included days to 50% flowering, days to physiological maturity, plant height, the number of capsules per plant, the number of seeds per capsule, 1000-seed weight, grain yield, biological yield, and the harvest index. After data collection, analysis of variance (ANOVA) was performed according to the experimental design to determine the significance of genotype effects on the studied traits. Statistical analyses were carried out using SAS 9.1, and mean comparisons with the control population (TN-82-747) were performed using the LSD test at the 0.05 probability level. Graphical analysis of genotype × trait relationships was conducted using GGE-biplot software to better understand the interrelationships among traits and genotypes.
Results: The results revealed considerable genetic variation among the studied samples for traits, including days to 50% flowering, days to physiological maturity, plant height, the number of seeds per capsule, thousand-seed weight, biological yield, and the harvest index. Seed yield ranged from 1,875 kg ha⁻¹ (TN-82-748) to 1,979 kg ha⁻¹ (TN-59-48). Genotypes G2, G3, G6, G7, G8, G9, G12, G14, G16, G17, G18, G19, G20, G21, G22, G24, G25, G26, G27, G30, and G35 showed higher values for days to maturity, days to 50% flowering, biological yield, and plant height, indicating lower desirability. In contrast, genotypes G4, G10, G11, G13, G15, G28, G32, G33, G34, and G36 were more desirable due to earliness and higher seed yields. Correlation analysis indicated positive correlations among days to maturity, days to 50% flowering, plant height, and biological yield. The number of seeds per capsule, thousand-seed weight, and the harvest index exhibited positive correlations with seed yield. However, the days to maturity trait was negatively correlated with both the harvest index and seed yield. In other words, late-maturing genotypes tended to produce more biomass and were more susceptible to lodging at the end of the growing season, which reduced both seed yield and the harvest index. 
Conclusion: G4, G10, G11, G13, G15, G28, G32, G33, G34, and G36 were identified as more desirable genotypes due to their earliness and higher seed yields. Among them, G36 and G32 demonstrated the greatest superiority in terms of seed yield and the harvest index, and can be considered promising genotypes for further evaluations in subsequent experiments.