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Differential Effects of Sodium/Calcium Ratio on Sorghum Genotypes

USDA-ARS, U.S. Salinity Lab., 4500 Glenwood Drive, Riverside, CA 92501

^* Corresponding author.

Plant response to salinity is a function not only of the total salt concentration but also of the Na/Ca ratio in the root medium. Calcium transport to the shoot decreases at high external Na/Ca and, in many gramineous species, Ca concentration in the expanding blades may become deficient. This study was initiated to determine the differential susceptibility of sorghum [Sorghum bicolor (L.) Moench] genotypes ‘NK 265’, ‘NB 9040’, and ‘Hegari’ (PI 34911) to the Na/Ca ratio in solution cultures. Plants were grown in the greenhouse with six Na/Ca ratios at two salinity levels (osmotic potentials = –0.4 and –0.6 MPa.) NK 265 and NB 9040 were sensitive to high Na/Ca molar ratios at both salinity levels (Na/Ca = 34.6 at –0.4 MPa and 52 at –0.6 MPa). Shoot growth was inhibited; blade injury was typical of severe Ca deficiency. In contrast, at –0.4 MPa, Hegari grew best at high substrate Na and the seedlings had no Ca deficiency symptoms. The K:Na selectivity ratios in Hegari shoots were lower than those in either NK 265 or NB 9040 shoots. The tolerance of Hegari to high external Na was attributed to efficient Ca transport to the developing blades. At both salinity levels, low Na/Ca ratio significantly reduced dry matter yield of Hegari shoots. In all three genotypes, shoot Na decreased with decreasing Na/Ca and was preferentially accumulated in the sheaths. The diversity of the sorghum genotypes in their response to external Na/Ca may be utilized by plant breeders to develop a line that is suited to sodic soil conditions.

Key Words: Calcium deficiency • Potassium/sodium selectivity • Salinity stress • Sorghum bicolor (L.) Moench

Received for publication August 7, 1987.

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