Susceptibility and tolerance of fenugreek (Trigonella foenum-graceum L.) to salt stress: Physiological and biochemical inspections

Greenhouse experiments were conducted to evaluate the effects of soil salinity on some physiological and biochemical attributes of fenugreek (Trigonella foenum-graecum L.) and its tolerance for salt using some empirical models. The treatments included different salinity levels of irrigation water (0.5, 2, 4, 6, 8, 10 and 12 dS/m) which were arranged in the form of a randomized complete block design with three replicates. Some physiological and biochemical properties were measured at the vegetative stage and trigonelline at seed ripening. As the results showed, salinity reduced leaf area, relative water content, water use efficiency, and leaf water potential, but it increased leaf thickness, greenness index, canopy temperature, sodium, ash, electrolyte leakage, malondialdehyde (MDA) and the other aldehydes. Salt stress also reduced photosynthetic pigments, chlorophyll a/b ratio, leaf soluble protein, potassium, K+/Na+ ratio, photochemical efficiency of photosystem II (PSII) and canopy air temperature difference (CATD) index. Like catalase (CAT) and ascorbate peroxidase (APX) activities, the activity of superoxide dismutase (SOD) was increased up to 6 dS/m and then decreased. Furthermore, proline concentration was increased up to 8 dS/m and decreased at higher salinities. The increased salinity enhanced seed trigonelline up to 6 dS/m and then decreased it. According to a linear model, the salinity threshold tolerance and the yield reduction slope were 1.28 dS/m and 4.9%, respectively. Nonlinear models, however, showed a yield reduction of 10%, 25% and 50% at the soil salinity of 3.38, 6.28 and 11.67 dS/m, respectively. The salinity tolerance index was found to be 12.24. Therefore, fenugreeks can be considered moderately sensitive to salinity at the vegetative growth stage. It may also be grown on slightly to moderately saline lands. Some characteristics may be considered as selective criteria to identify the cultivars of fenugreek that tolerate salt stress.