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.