Evaluation of morphological traits and yield and yield components of oilseed flax (Linum usitatissimum L.) genotypes in response to deficit irrigation regimes

Introduction Arid and semi-arid regions of the world are primarily characterized by water scarcity, which limits agriculture mainly to irrigated land. Presently and in the future, irrigated farming systems will have to operate under conditions of water scarcity, which significantly impacts food production and threatens global food security. Deficit irrigation is an important strategy involving the application of limited irrigation during drought-sensitive phenological stages of a crop. Water restriction is targeted at drought-tolerant growth stages, particularly the vegetative stages and late stages of ripening. The response of plants to deficit irrigation-induced water stress varies with growth stages and stress intensity. Deficit irrigation can maximize crop water productivity without significant yield loss, and various deficit irrigation strategies have been developed to improve crop performance under water deficit conditions. However, it is crucial to develop crop management strategies aimed at enhancing crop sustainability in stressful environmental conditions. Therefore, our study aimed to investigate the influence of different irrigation regimes at various growth stages on the morphological characteristics, and oil and grain yield of oilseed flax genotypes. Materials and methods This experiment was carried out during the 2022-2023 growing season, using a split-plot arrangement in a randomized complete block design with three replications. The study site was located at the research farm of Shahid Chamran University of Ahvaz, Iran. The main plots consisted of four irrigation regimes: control (irrigation at 80%, 80%, 80%, and 80% of field capacity), mild water deficit (irrigation at 60%, 70%, 70%, and 60% of field capacity), moderate water deficit (irrigation at 60%, 60%, 60%, and 60% of field capacity) and severe water deficit (irrigation at 40%, 50%, 50%, and 40% of field capacity). The sub-plots consisted of four oilseed flax genotypes: Isfahan, Kerman, Indian and Hungarian. Deficit irrigation treatments were applied at stem elongation, branching, flowering, and seed-filling stages. The control treatment was watered with sufficient water (80% field capacity) until the end of the experiment. Results and discussion There were significant differences among genotypes and irrigation regimes in most traits. Deficit irrigation depend on plant growth stage and stress severity led to a significant reduction in the number of capsule per plant, the number of grain per capsule, grain number per plant, grain weight per plant, 1000-grain weight, plant height, branch number, biomass yield, harvest index, and grain and oil yield. The grain yield of all genotypes significantly decreased under mild, moderate and severe water-deficit stresses by 34%, 39% and 49%, respectively, compared to the control. Similarly, the oil yield reduced by 35%, 40%, and 52%, respectively, compared to the control. There was genetic variation in grain yield between genotypes in response to water deficit. Grain yield was significantly reduced for all genotypes in response to severe water-deficit stress, with larger reductions in Indian and Hungarian genotypes (56 and 62%, respectively) than Isfahan and Kerman genotypes (with 46 and 32%, respectively). The Isfahan and Kerman genotypes with higher grain yield exhibited a higher oil yield. Conclusion Different irrigation regimes applied at various growth stages had different effects on the morphological traits and yield of oil seed flax genotypes. The developmental stage and severity of water deficiency played an important role in the genotype responses to deficit irrigation management. The moderate deficit regime led to a 37% and 29% decrease in grain yield of Isfahan and Kerman genotypes, respectively, while saving about 35% of available water. Therefore, this deficit irrigation regime is recommended as a suitable strategy to improve water productivity. Moreover, Isfahan and Kerman genotypes are recommended for cultivation in semi-arid regions due to their greater stability in grain yield under deficit irrigation conditions.