Evaluation of genetic diversity and drought tolerance in safflower genotypes based on morphological traits and seed yield in Hamedan

Introduction: Safflower (Carthamus tinctorius L.) is a drought-tolerant crop valued for its high-quality edible oil and natural colorants in various industries. Its adaptability to semi-arid climates and multipurpose utilization of plant biomass position it as a strategic crop for sustainable agriculture in water-limited regions.
Materials and Methods: This study investigated the effects of terminal drought stress on yield components, seed and oil yield, and drought-related morphological traits in promising safflower genotypes. The experiment was conducted as a split-plot arrangement within a randomized complete block design (RCBD) with three replications at the research fields of Bu-Ali Sina University, Hamedan, during the 2022–2023 growing season. The main factor consisted of two irrigation regimes: well-watered (control) and terminal drought stress (imposed from flowering to seed maturity). The sub-plot factor comprised five safflower genotypes: Sofeh, Amir, Parnian, Zis-chini, and Goldasht.
Results: The analysis of variance (ANOVA) results showed that the irrigation regime had a statistically significant effect on all morphological traits (except leaf area), oil percentage, and yield-related traits. The genotype × irrigation regime interaction was significant for plant height, number of lateral branches, capitulum diameter, and oil percentage, indicating differential genotypic responses to water deficit stress. Mean comparison analysis demonstrated that the genotype Sofeh exhibited the greatest grain yield stability, with yields of 341 g.m⁻² under full irrigation and 315 g.m⁻² under drought stress (a 7.6% reduction). In contrast, although the genotype Parnian possessed a high initial oil content (44.6%), it experienced a substantial decline to 32.7% under water deficit conditions. Thousand-seed weight and the weight of 20 capitula were identified as stable traits across irrigation treatments. The genotype Sofeh maintained stem diameter, leaf area, and total capitulum weight, demonstrating superior efficiency in resource allocation toward reproductive organs. Overall, Sofeh was identified as a late-season drought-tolerant genotype, owing to its combination of high yield, stable oil content, and minimal reduction in yield components.Furthermore, factor analysis based on pooled data from both well-watered and stress conditions extracted three factors with eigenvalues greater than one, collectively accounting for 77.7% of the total variation in the dataset. Factor 1 (38.9% of variance) was interpreted as a yield and overall production potential factor; Factor 2 (19.8% of variance) represented a vegetative and morphological traits factor; and Factor 3 (18.9% of variance) was designated as a seed and capitulum size factor.
Conclusion: Owing to its high yield potential, superior performance stability under water deficit, and relative resilience in maintaining oil content, the Sofeh genotype is recommended as the most promising candidate for cultivation in water-limited regions and as a parental line in breeding programs aimed at developing drought-tolerant safflower cultivars. Furthermore, the findings underscore that simultaneous selection for high yield, optimal seed size, and stable oil content under drought conditions necessitates the application of multi-trait selection indices and careful consideration of genotype × environment interactions.
Conclusion: Owing to its high yield potential, superior performance stability under water deficit, and relative resilience in maintaining oil content, the Sofeh genotype is recommended as the most promising candidate for cultivation in water-limited regions and as a parental line in breeding programs aimed at developing drought-tolerant safflower cultivars. Furthermore, the findings underscore that simultaneous selection for high yield, optimal seed size, and stable oil content under drought conditions necessitates the application of multi-trait selection indices and careful consideration.