Salt Tolerance of Soybean Varieties ( Glycine max L. Merrill) During Germination and Later Growth 1

ACCUMULATION of salts in the irrigated soils of western United States often results in reduction of seed germination and planet growth, Plant genera and species may differ widely in salt tolerance but, for most crops, varietal differences in salt tolerance are very small. Approximately a third of the soils of the Imperial Valley of southern California are excessively saline and are usually cropped to the more salt tolerant crop species. Ogasa (12) found ~:hat seed germination of soybean variety ~KO 561’ was inhibited by a 0.2% NaC1 solution at 30° C. but it was necessary to increase the concentration to 0,3% NaC1 to cause inhibition at 15° C. The data of Uhvits (15) show that at osmotic pressures greater than atmospheres, alfalfa seed germination in solution cultures was retarded considerably more by concentrations of NaC1 than by mannitol presumably because of the toxic effect of the salt. Rudolfs (13) found seed water absorption in 15 hours was decreased 9% when the osmotic pressure of the germinating solution was increased from 0 to 7 atmospheres with addition of NaC1. Ayers and Hayward (2) showed that salt tolerance during seed germination is not always positively correlated with that of the crop during later growth. The first physiological reaction of plants immediately after an increase in soil salinity is reduced entry of water in roots (3, 9). Reduced growth, which is not yet clearly understood, follows. Reduced growth is evident in reduced height and development of smaller, darker green leaves (6, 8, lo). The characteristic chloride toxicity symptoms for peach, citrus, and a number of other trees are incipient chlorosis accompanied by drying and browning of the leaf beginning at the margin of the apex. The minimal levels of chloride accumulation associated with leaf burn o.f several fruit trees ranged from 5,000 ppm ~co 18,000 ppm chloride (4). Leaves of field, vegetable, and forage crops which usually showed no specific chloride injury in salinized soil ranged from 17,750 ppm to 53,000 ppm chlorides. Bernstein and Ayers (5) found no relation between chloride content and salt tolerance in green beans. In their studies, 6 varieties of green beans all accumulated large amounts of chloride. Although barley (1) and co~ton (11) were considered highly salt tolerant, varietal differences in salinity effects on seed yield were reported. Salt decreased the vegetative portions of barley and wheat relatively more than that of the grain (1). The ’Lee’ soybean variety was rated moderately salt tolerant in studies at the U.S. Salinity Laboratory at Riverside, California, a in 1955. In this study, seed yields were reduced 50% when the electrical conductivity of the saturation extract of the soil, (ECe) was 9 millimhos/cm. Oil percentage decreased and protein percentage increased slightly. Preliminary studies with 50 soybean strains adapted to