Root Control of Leaf Phosphorus and Chlorine Accumulation in Soybean under Salinity Stress1

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Abstract
Some soybean cultivars [Glycine max(L.) Merr.] grown in saline (−0.34 MPa osmotic potential) solution cultures with inorganic phosphate ≥ 0.25 mM, accumulate excessive P and Cl in their leaves. Greenhouse experiments were conducted with reciprocally grafted soybean to evaluate the role of the scion and rootstock on leaf P and Cl accumulation and foliar injury. Four distinctly different genotypes were studied. ‘Lee’ and ‘Lee 74’ are described as leaf‐Cl excluders, whereas ‘Clark 63’ and ‘Jackson’ are leaf‐Cl accumulators. Clark 63 and Lee 74 accumulate excessive amounts of P in their leaves, whereas Lee and Jackson do not. Root‐scion grafts of all combinations of the four cultivars, including self‐grafts were made and tested. Visual foliar injury, its onset, severity, and symptoms, was controlled predominantly by the genotype of the rootstock and was correlated with leaf P and Cl concentration. Thus, scions of all four genotypes when grafted on rootstocks that translocate P and Cl to the shoots, were sensitive to P and Cl. Scions on Clark 63 rootstocks were killed and necrotic leaves were beige in color. Since leaf P and Cl exceeded 550 and 600 mmol kg−1dry wt (1.7% P and 2.1% Cl) we attributed this injury to combined P and Cl toxicity. Leaves of scions on Lee 74 rootstocks were severely injured and exhibited a distinctive reddish‐brown coloration indicative of P toxicity. Scions on Jackson rootstocks exhibited only moderate foliar injury. Injured leaves were chlorotic and necrotic along the margins characteristic of Cl toxicity. Scions on Lee rootstocks remained healthy during the entire experiment and leaf P and Cl were maintained below 405 and 275 mmol kg−1dry wt, respectively. Although leaf P and Cl accumulation were controlled predominantly by the genotype of the rootstock, an additional mechanism, as yet unidentified, was found in the scion of Lee and Lee 74 that reduced leaf P and Cl concentration. The contribution of the mechanism was not sufficient to delay the onset of foliar injury.

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