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Salinity stress is one of the most vital abiotic stresses which limits the production of crops. In recent decades, the area under chickpea cultivation in Iran has tripled, but unfortunately, its yield has decreased from 610 to 500 Kg per hectare. The main reason for this reduction is the allocation of marginal lands under rain-fed conditions to chickpea cultivation. However, environmental stresses are the most critical factors of yield loss that can decrease chickpeas production significantly. The growth of chickpea is susceptible to salinity, and salinity stress affects their yield by affecting plant growth and symbiotic bacteria. Considering the current extent of salt-affected lands in Iran and in order to maintain and increase the area under chickpea cultivation, it is necessary to select the salt-tolerant genotypes. Therefore, this study was carried out to determining the salinity tolerance threshold of Kabuli -type chickpea genotypes.

The experiment was a split-plot randomized complete block design (RCBD) with three replicates at the research greenhouse of the faculty of agriculture of Ferdowsi University of Mashhad, Iran, in 2020. Chickpea germplasm, including 70 Kabuli type chickpea genotypes, were provided from the Mashhad chickpea collection at the Research Center for Plant Science, Ferdowsi University of Mashhad. Two weeks after seed planting, the salinity treatments included 12 and 16 dS.m-1 sodium chloride and 0.5 dS.m-1 (tap water) as control was applied. The recirculating nutrient system was applied, the nutrient solution was replaced weekly, and the salinity of nutrient solution was adjusted daily, but no acidity adjustments were made in the Hoagland solution. The plant height was measured before and after four weeks of applying salinity stress, and then the difference in plant height was calculated. Four weeks after salinity application, survival percentage, leaves survival, plant height, leaf electrolyte leakage, osmotic potential, shoot dry weight, and Na to K ratio were measured. Salinity tolerance indexes, including stress tolerance (TOL), mean productivity (MP), stress susceptibility index (SSI), geometric mean productivity (GMP), and stress tolerance index (STI), were calculated based on the shoot dry weight and separately for 12 and 16 dS.m-1 compared to the control treatment. Data were analyzed using Minitab 16 software, and the mean comparison was performed by Duncan Multiple Range Test (DMRT) at a 5% probability level. Interrelationship among different traits was calculated using Pearson's correlation analysis. STATISTICA 8.0 and SPSS 27 soft wares also performed a cluster analysis (based on Euclidean distance) and principal component analysis (PCA).

The results showed that for the salinity levels of 12 and 16 dS.m-1, 65 and 28 genotypes had a survival between 76 -100%, respectively. With the decrease in the survival percentage in 16 dS.m-1, the average percentage of leaf survival also decreased. With increased salinity levels from 12 to 16 dS.m-1, electrolyte leakage in the survival range of 76 -100, 51 -75, and 26 -50% increased by 8, 25, and 12%, respectively. With increased salinity levels from 12 to 16 dS.m-1, in survival ranges of 0 -25, 26 -50, 51 -75, and 76 -100%, shoot dry weight decreased by 15, 11, 36, and 14%. With increased salinity levels from 12 to 16 dS.m-1, the shoot Na to K ratio in the survival range of 26-50% did not change, and in the survival range of 0 -25, 51 -75 and 76 -100%, it increased two and nine times and 22% respectively. The highest average shoot Na to K ratio was also observed within the survival range of 0 -25%. In 12 and 16 dS.m-1, two genotypes, MCC1467 and MCC1394, were superior to other genotypes in most studied traits. The genotypes of the third cluster had a higher relative advantage for salinity tolerance.

In general, the results showed the diversity between chickpea genotypes under salinity stress. In 12 and 16 dS.m-1 salinity, MCC1467 and MCC1394 were superior to other genotypes in most studied traits. In saline conditions plant survival had a positive and strong correlation with leaf survival. In the saline condition, genotypes that can maintain their normal physiological function can maintain and expand more leaf area, which ultimately leads to more biomass production. The genotypes of the third cluster had a more advantage for salinity tolerance. Due to this study being conducted in greenhouse conditions, it is recommended to check the salinity tolerance of superior genotypes in field conditions.