Growth and nutrient composition of Ca2+ use efficient and Ca2+ use inefficient genotypes of tomato

The response of two tomato lines (Lycopersicon esculentum Mill. Ca²⁺ use efficient line 113 and Ca²⁺ use inefficient line 67) to a range of constant low Ca²⁺ concentrations was investigated in a sand culture system. Four Ca²⁺ concentrations were established and maintained throughout the experiment: 0.038, 0.75, 1.51 and 3.75 mM CaCl₂ on a constant background of 1.1 mM NaCl. Response to Ca²⁺ was determined by analysis of growth parameters and of shoot Ca²⁺, Na⁺, K⁺ and Cl⁻ concentrations. Differences in Ca²⁺ and K⁺ use efficiencies were expressed as the calcium utilization efficiency ratio, or CaER, and potassium utilization efficiency ratio, or KER, (mg of dry weight produced·mg⁻¹ of Ca²⁺ or K⁺ in plant). Dry weight production of line 113 was significantly higher than line 67, and was associated with a higher CaER and KER. The Ca²⁺ treatments differentially affected shoot Ca²⁺, Na⁺, Cl⁻ and K⁺ concentrations. As expected, shoot Ca²⁺ and Cl⁻ concentrations increased whereas Na⁺ concentration decreased with Ca²⁺ treatments. Line 113 had more than twice the amount of Na⁺ in shoot tissue than line 67. The K⁺ to Na⁺ ratio was twice as high in line 67 than in line 113. No evidence for higher soluble Ca²⁺ contributing to higher Ca²⁺ utilization was observed. The relationship between Ca²⁺ use efficiency and growth was not correlated with higher percentages of soluble Ca²⁺ in leaf tissue or with differences in root morphology. Differences in Ca²⁺ use efficiency alone could not explain the higher growth rate in line 113. This study demonstrated that the physiological factors involved in the genetic control of Ca²⁺ use efficiency should be assessed under a range of constant low Ca²⁺ concentrations in order to observe the physiological changes taking place. Thus, the use of Ca²⁺ deficient conditions are to be avoided as it may interfere with the expression of the physiological factors involved in Ca²⁺ use efficiency.