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This research was conducted to investigate the effects of salt stress on seed germination, emergence, yield and yield component of fenugreek at National Salinity Research Center during 2018-21. Seeds of five ecotypes, including Hendi, Ardestani, Isfahani, Neyrizi and Mashhadi, were compared at different salinity levels (0, 3, 6, 9, 12, 15, 18, 21, 24, 27 dS/m for germination and 0.5, 3, 6, 9, 12, 15, 18 dS/m for emergence stages. The statistical design was completely randomized in the form of a factorial experiment with three replications. This research was conducted in a greenhouse for studying the effect of different salinity levels on morpho-physiological and yield parameters. Results showed that at the germination stage, increasing in salinity up to 6 dS/m had no effect on germination percentage, however, at higher salinity levels, the germination percentage gradually decreased. Seed germination rate gradually decreased with increasing salinity stress. This reduction was not significant for Ardestani and Neyrizi up to 3 dS/m and for Isfahani, Hendi and Mashhadi up to 6 dS/m. Increasing salinity up to 3 dS/m had no significant effect on seed emergence percentage and thereafter, the amount of emergence percent was significantly decreased. The highest amount of seed emergence rate was belonging to Hendi and Neyrizi and the least to Ardestani ecotype. Based on the results, salinity reduced shoot height, number of leaves, number of branches, number of nodes, stem diameter, internode length, leaf area, root to shoot ratio, relative water content, leaf water potential, photochemical efficiency, water use efficiency and increased leaf greenness, canopy temperature and electrolyte leakage. Salt stress also reduced pod length, pod weight, number of seeds per pod, number of pods per plant, number of filled seeds per plant, filled to unfilled seeds ratio, shoot dry weight, straw weight, thousand-seed weight, grain yield, harvest index and increased percentage of unfilled seeds, trigonelline and seed alkaloid. Based on results, the salt tolerance threshold of fenugreek at germination stage was 21.83 dS/m, with a reduction slope of 17.09%. Although the Isfahani ecotype had a lower salt tolerance threshold (20.32 dS/m), it had the lowest reduction slope (10.37%), as well. Results of nonlinear models also showed that the highest salinity in which seeds were germinated by 50% (25.81 dS/m), was obtained from Isfahani ecotype. At the emergence stage, the mean salt tolerance threshold of fenugreek was 4.14 dS/m, with a reduction slope of 4.63%. Results showed that at vegetative stage the fenugreek salt tolerance threshold and the slope of yield reduction was 1.28dS/m and 4.91 percent, respectively. However, according to non-linear models, a reduction of 10 and 25 percent in relative grain yield occurred at 3.38 and 6.28 dS/m, respectively. According to the results of this study, the salinity at which the relative grain yield decreased by 50% percent was observed at soil salinity of 11.67dS/m. Based on the linear model, the fenugreek salt tolerance threshold and the slope of seed yield reduction was 1.30 dS/m and 8.64 percent, respectively. However, according to non-linear models, a reduction of 10 and 25 percent in relative grain yield occurred at 2.46 and 4.19 dS/m, respectively. According to the results of this study, the salinity at which the relative grain yield decreased by 50% percent (EC50) was observed at soil salinity of 6.51 dS/m. Therefore, the salt tolerance of fenugreek varies throughout different growth stages, the maximum salt tolerance was related to germination and thereafter emergence. The lowest salt tolerance was observed for the reproductive stage. Based on both the salinity tolerance threshold, the slope of seed yield reduction, and the salinity tolerance index, fenugreeks can be classified into the group of moderately sensitive to salinity plants.Key words: emergence, germination, growth, seed, tolerance, yield
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