Partitioning of chloride ion in the germinating seed of two forage legumes under varied salinity and temperature regimes

Laboratory studies were conducted to investigate the partitioning of chloride (Cl) ions in the germinating seed of two forage legumes, Sesbania (Sesbania sesban) and Snail Medic (Medicago scutellata), under varied salinities and temperatures. Seeds were placed in Petri dishes containing 20 mL of saline solutions of varied electrical conductivities (0.01, 6.4, 12.2, 17.4, 22.6, 27.2, and 32.1 d/Sm) prepared with sodium chloride (NaCl). The germination temperatures were 10, 20, 30, and 40 degrees C. Germination counts were taken every two days for eight days and the result was used to calculate germination rate index. On Day 8, seeds were separated into seed coat, cotyledon, and embryo, and analyzed separately for Cl. Generally, Cl concentration increased in the different seed components with increase in salinity and temperature. High Cl accumulation in the embryo was associated with germination failure. However, apart from the toxic effect of high embryo Cl content, high temperatures may also have a direct adverse effect on embryo viability. At the optimum germination temperatures (30 degrees C for Sesbania and 20 degrees C for Snail Medic), the salinities that reduced germination by 50% were 18.5 and 15.0 d/Sm in Sesbania and Snail Medic, respectively; embryo Cl concentrations were 6.83 to 8.90 mmol/g DW in Sesbania and 6.42 to 7.42 mmol/g in Snail Medic. Although, Sesbania was slightly more tolerant to salinity than Snail Medic during germination, both were classified as being moderately tolerant.