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Iron Utilization by Efficient and Inefficient Sorghum Lines¹

Iron-efficient and Fe-inefficient sorghum [Sorghum bicolor (L.) Moench.] inbred lines and their F₁ hybrid differed in response to Fe deficiency. These lines were used in growth chamber studies with a soil and with several liquid-nutrient media to determine Fe-use efficiency. An Fe-deficient Colby silt loam soil (5.2 ppm DTPA extractable Fe) with 22.4 kg Fe/ha and without added Fe was used for a potted-soil, growth study. In the remaining studies seedlings were grown in Hoagland nutrient solution to induce Fe deficiency, to determine effects of P levels and Fe sources, and to measure root reduction potential. The respective solutions used were: (i) 0.2-strength solution with no Fe; 2.0 µM Fe and 3.0 mg CaCO₃/ liter; 2.0 µM Fe and 5.0 mM P; 2.0 M Fe and 2.5, 25.0, and 10.0 µM Cu, Mn, and Zn, respectively; (ii) 0.5-strength solution with 10.0 µM Fe at O, 0.5, 1.0, 2.5, and 5.0 mM levels of P; (iii) 0.5-strength solution with 10.0 µM ferric and ferrous Fe; (iv) 0.2-strength solution containing 2.0 µM Fe with the last 24 hours' growth in a ferrichloride-ferricyanide solution.

Plants from all studies were separated to roots and shoots, wet-ash digested, and assayed for Fe, Cu, Mn, Zn, Ca, and Mg by atomic absorption spectrophotometry. Phosphorus was determined by the vanadomolybdophosphoric method.

The Fe-efficient inbred usually maintained lower P concentrations in shoots and commonly in roots under Fedeficient conditions. Antagonism from other nutrients except P was not involved consistently in differential response of Fe-efficient and Fe-inefficient lines. Root reduction potential for ferrichloride-ferricyanide was lower for sorghum than for other crops, but did not differ between inbred lines. Shoot and root growth was always greater with ferrous than with ferric Fe. Efficiency of Fe use by sorghum apparently was not inherited by the hybrid. Iron efficiency in sorghum probably can be improved by accumulating genes that increase uptake of Fe, or by decreasing interference of P in utilization of Fe.

Key Words: Chlorosis • Nutrient deficiencies • Nutrient antagonism • Genetics

² Graduate Research Assistant, Associate Professor, and Professor, Dept. of Agronomy; and Research Agronomist, PSRD, ARS, USDA, respectively, Kansas State University, Manhattan 66506.

Received for publication March 6, 1972.