Variation in salt tolerance of alfalfa

Abstract

Abstract Identification of crop germplasm tolerant to relatively high levels of salinity will allow more extensive use of lands characterized as marginal due to salt accumulation. Two experiments were conducted to identify and evaluate germination salt tolerance in various alfalfa (Medicago sativa L.) cultivars, breeding lines, introductions, and germplasms (populations). In the first experiment, 229 alfalfa populations from North Africa, Asia, the Middle East, and the United States were germinated in sodium chloride (NaCl) solutions with concentrations of 0, 44, 88, 132, or 176 mM (10 mM = 640 mgL−1 = 0.1 Sm−1 = 1.0 mmhos cm−1) at 25°C. When expressed as a proportion of the no‐salt control, significant germination differences were observed in the 229 populations. Twenty‐nine populations that exhibited the highest germination at 176 mM in the first experiment were retested in NaCl concentrations of 0, 44, 88, 132, 176, 220, 264, 308, or 352 mM. The 29 populations differed noticeably when treated with NaCl concentrations. Speed of germination, leaf number, lateral root number, and seedling height all decreased significantly as salt concentrations increased. There were no significant differences in germination percentages between 0 and 44 or between 132 and 176 mM, but there were significant differences between all other consecutive treatment levels. Germination percentages significantly decreased when NaCl concentrations exceeded 220 mM. Germination was inhibited in most populations at 352 mM (352 mM = 2% NaCl). Our research clearly demonstrates that genetic diversity for salt tolerance exists among alfalfa populations during germination. These populations, when combined with salt‐tolerant Rhizobium, should provide potential nitrogen‐fixing symbionts that can be used on moderately saline soils.