Phosphorus Efficiency as Related to Iron Inefficiency in Sorghum

Abstract

AbstractSorghum (Sorghum bicolor L. Moench) is often grown on alkaline soils, and the plants frequently develop symptoms of Fe deficiency. The susceptibility is dependent on the ability of the plant to respond to Fe stress. This adaptive response is genetically controlled whereby H+ ions and a reductant are released from the roots. These make Fe available for uptake by the plant. Activation is greatest in Fe‐efficient plants and least in Fe‐inefficient plants. Phosphate accumulation and Fe‐stress response oppose each other in plant use of Fe. In this study, accumulation of phosphate and Fe‐stress response were evaluated as causes of Fe chlorosis in four sorghum cultivars that differ in uptake of P and in susceptibility to Fe chlorosis. The seedlings were first grown in a light chamber on a complete nutrient solution at, pH 4.3 until the plants were large enough for use. They were then transferred to nutrient solutions with Fe, P, NH4‐N or NO3‐N as variables. The pH of the nutrient solution, reductant in nutrient solution, and uptake of Fe and P by the plant were determined. The Fe‐efficient KS5 and ‘Pioneer 846’ sorghums released more reductant from their roots, took up more Fe, and contained less P than the Fe‐inefficient “B‐line” and ‘Wheatland’ cultivars. The release of H+ ions by roots was somewhat comparable in all four sorghum lines. On Bladen soil (pH 4.3—high in Al), KS5 and Pioneer 846 took up less P than the “B‐line” and Wheatland sorghum. Phosphorus efficiency in the four cultivars is “B‐line” ≥ Wheatland > Pioneer‐846 > KS5. In addition, KS5 developed iron chlorosis, which implies that KS5 cannot utilize either P or Fe in Bladen soil. Accumulation of P and insufficient Fe‐stress response both appear to be causative factors of Fe deficiency in “B‐line” and Wheatland sorghum.