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Abstract
Experiments were conducted with sorghum {Sorghum bicolor (L.) Moench} to (a) determine optimum conditions to screen for differential responses of genotypes to Fe deficiency in nutrient solutions, (b) compare responses of nutrient solution-grown plants to soil-grown plants, and (c) determine some of the physiological and chemical properties of genotypes considered to be both tolerant and susceptible to Fe deficiencies. Plants were grown in nutrient solutions and soils under growth chamber and greenhouse conditions. Iron deficiencies were imposed on the plants by (1) adding varied amounts of Fe, (2) adding higher than normal levels of P, (3) adding high levels of CaCO(,3), (4) using different sources of N, and (5) using low Fe soils. Parameters used to measure some aspects of differential responses of the genotypes to Fe and the physiological and chemical properties were the degree Fe deficiency symptoms in the upper leaves, dry-matter yields, dry-matter produced/unit Fe, Fe concentrations and contents, top/root dry-matter and Fe ratios, distribution of Fe among upper and lower leaves, pH changes in nutrient solutions, 'reductant' (phenolic compounds) released by roots in nutrient solutions, leaf surface areas and plant heights, leaf chlorophyll concentrations, and concentrations of P, K, Ca, Mg, S, Mn, Cu, and Zn and their possible interaction with Fe in leaves and roots.
In nutrient solution screening, plants grown with higher than normal P and with NO(,3)('-) as the sole source of N became Fe deficient more rapidly and gave wider differential responses to Fe deficiency than other treatments used to induce Fe deficiency. Extensive differences and intensity of Fe deficiency symptoms appeared in plants treated at 7 and 10 days of age but not in 14-day-old plants. Of the 46 U.S. and 10 Nigerian genotypes screened for differential Fe deficiency, SC 118-15E, Martin, Redlan, CK 60, TAM 428, SC 369-3-1JB, SC 500-6-1, SC 134, TX 415, TX 07, SC 29, and KS 57 (U.S.), and C 74, FFB-L, and HP 3 (Nigerian) were more 'Fe-inefficient' or susceptible to Fe deficiency, and SC 33-9-8-E4, Norghum, KS 5, Plainsman, a North Platte line, TX 412, SD 106, and SC 149 (U.S.), and KANO L-1, and RZ 1 (Nigerian) were more 'Fe-efficient' or tolerant to Fe deficiency. Most likely because of higher Mn and Cu in soils, genotypes grown on low Fe soils did not generally rank the same in Fe deficiency symptoms as they did when grown in nutrient solutions.
Selected genotypes which showed relatively wide differential Fe deficiency responses were used to study additional physiological and chemical properties associated with Fe deficiency. The genotypes differed in the degree of Fe deficiency symptoms, dry-matter yields, Fe concentrations and contents, dry-matter produced/unit Fe, distribution of Fe, chlorophyll concentrations, leaf areas, plant heights, other element (especially Mn and Cu) concentrations, and 'reductant' released. Differences in nutrient solution pH did not distinguish differences in genotype response to Fe. SC 33-9-8-E4 ('Fe-efficient') had lower Mn and Mn/Fe ratios than SC 118-15E ('Fe-inefficient'). Iron concentration in Fe deficient tissue was not necessarily lower than in green tissue.
