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Phosphorus Enhancement of Salt Tolerance of Tomato

Biological and Chemical Res. Inst. (BCRI), PMB 10, Rydalmere, 2116, New South Wales, Australia
Dep. of Agriculture, Univ. of Queensland, St. Lucia, 4067, Australia
Dep. of Agronomy, Univ. of Sydney, Sydney, 2006, Australia

^* Corresponding author.

Increasing plant P supply has been shown to either increase or decrease the salt tolerance of many plants. Tomato plants (Lycopersicon esculentum Mill.) were grown in a greenhouse in a continuously flowing solution culture system to investigate whether P fertilization modified the detrimental effects of NaCl at low constant P concentrations similar to those in soil solutions. Increasing P fertilization enhanced the tolerance of tomato plants to NaCl. At 0.1, 1.0, and 10 mM P, the NaCl concentrations that reduced yields of fruit by 50% were 58,72, and 130 mM, respectively. Salinity reduced foliar P concentrations. This may have been mediated partly through ionic strength effects, which decreased the activity of H₂PO₄^–1 by about 40%. Plants grown under saline conditions had higher internal P requirements. When the NaCl concentration was increased from 10 to 50 and 100 mM, the corresponding concentrations of P in the youngest mature leaf required to obtain 50% yield were increased from 1.8 to 2.4 and 3.0 g kg^–1. The change in internal P requirement was also evident by the relative severity of foliar symptoms of P deficiency in plants growing in the saline treatments at any given foliar P concentration. Adequate P nutrition was essential for effective ionic compartmentation. Under saline conditions, increasing the solution P concentration from 1.0 to 10 µM decreased Na and increased K concentrations in immature leaves but increased Na and decreased K in the mature leaves. Accumulation of ions for osmotic adjustment and restriction of Na and Cl accumulation in immature leaves appear to be involved in P enhancement of salt tolerance of tomato plants.

Joint publication of the BCRI and the Universities of Sydney and Queensland.

Received for publication October 28, 1988.

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