Differential resistance of weeping lovegrass genotypes to iron?related chlorosis

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Abstract
Genotypes of weeping lovegraes (Eragrostis curvula (Schrad.) Nees) differ widely in resistance to an Fe‐related chlorosis on certain calcareous soils. To explore the physiology of this relationship in greater detail, chlorosis‐resistant FQ 22 and chlorosis‐susceptible FQ 71 genotypes were grown in nutrient solutions containing 1 ppm Fe (half as NaFeEDTA and half as FeSO4.7H20) at initial pH 4.0. When the solution pH was left unadjusted, the FQ 71 quickly increased the pH of the medium from 4.0 to the range of 6.5 to 7.0; iron was visibly precipitated within the solutions and on plant root surfaces; and plant tops became chlorotic. Under the same conditions, the FQ 22 maintained the solution pH within the range of 4.0 to 4.9; nutrient solutions remained clear; roots were white; and plant tops were green. FQ 22 absorbed 5 times as much NH+ 4 as FQ 71. When nutrient solutions were adjusted to pH 4.0 daily, both genotypes grew well and remained green; nutrient solutions were clear; and all roots were white. The chlorosis‐resistant FQ 22 genotype accumulated higher concentrations of Fe and lower concentrations of Mn and Ca in its tops than did the chlorosis‐susceptible FQ 71. Superior chlorosis resistance of the FQ 22 genotypes (compared with FQ 71) was associated with the ability to maintain a low pH in its root zone (which prevents Fe precipitation), a greater affinity for NH+ 4‐N, more effective transport of Fe from roots to tops, and restricted transport of Mn end Ca. Excesses of these elements (Mn and Ca) nay interfere with the metabolism of transported Fe in the tops of the chlorosis‐susceptible FQ 71 genotype.