RELATION OF CHLOROSIS TO CONCENTRATION OF IRON IN CITRUS LEAVES

Abstract

SEVERAL INVE$TIGATORS have adopted the concept that iron chlorosis is caused by physiological unavailability of iron in the tissues. The evidence presented here indicates that this concept is not valid, at least as far as citrus is concerned, anid that iron chlorosis involhes a simple deficiency of iron in the leaf. Visible symuptoms of iron chlorosis (lime-induced chlorosis) in citrus leaves are similar to those found in many other crop plants, namely, green veins sharply distinguished from a less g,reeni or yellow mesophyll. These symptoms are attributed to improper iron nutrition on the basis of the following evidence: (1) the leaf pattern can sometinies be cured by applying iron to the soil or other nutrient medium; and (2) affected leaves usually respond witl increased greenness to surface application of iron solutions, but such response does not result from applications of other nutrient elements (see discussion bv Jljin, 1952). Nutrient deficiencies are generallv accompanied by low concentrations of the deficient elements' in certain plant organs, particularly leaves (Goodall and Gregory, 1947)Although some investigators have reported this situation with iron in lime-induced chlorosis (e.g., Gile and Carrero, 1920; Menchikowsky and Puffeles, 1935), many have failed to find consistent differences in iron concentrations in chlorotic and healthy leaves (Ilj in. 1952 McGeorge, 1949; Wallace. 1928) . From this situation came the idea that not all the iron in chlorotic leaves is metabolically active; supportling evidence was supplied by Oserkowsky (1933!who showed that iron extracted from leaves by 0.3 N HCI correlated well with chlorophyll content. The conc.ept of physiological unavailabilitv of iron still appears to be prevalent (Leeper, 1952) in spite of the demonstration by Jacobson (1945) that. after thorouglh removal of surface contamination from the fresh leaves of some deciduous fruit trees, total iron content correlated well with chlorophyll content. The work of Smith et al. (1950), in Florida, indicates that this correjation probably holds also in citrus leaves. Their studies support the conclusion of Jacobson that iron-contaminants such