NITRIC-ACID-EXTRACTABLE AND O-PHENANTHROLINE-EXTRACTABLE IRON FOR DIAGNOSIS OF IRON CHLOROSIS IN CITRUS LEMON TREES

Plant analysis for total iron (Fe) is frequency used for diagnosis of Fe-deficiency chlorosis. However, chlorotic plants frequency contained similar or higher amount of total Fe than the healthy green plants. T he objectives of this study were to (i) determine if Fe chlorosis in c itrus lemon can be diagnosed by total or active Fe and can be related to the degree of chlorosis, and (ii) determine the optimum extraction time and ratio of extracting solution to plant sample for extracting t he active Fe. Leaf samples of different degrees of Fi: chlorosis were sampled from different citrus lemon trees from three different sites. Total Fe was extracted with nitric acid (HNO3) and active Fe with o-ph enanthroline from lemon leaves. An extraction time of 20 and 45 hours and the ratios of the extractor to the sample of 5:1, 10:1, and 20:1 w ere investigated. The results indicated that an extraction rime of 20 hours is enough for extracting the active Fe from citrus lemon leaves by o-phenanthroline. The amount extracted by all ratios (5:1, IO:1, an d 20:1) were detectable and at the same time similarly and consistency showed the differences in degrees of chlorosis in all plant samples. Total Fe content was always higher in moderately and severely chloroti c leaves compared to the green leaves and was not related to the degre e of chlorosis. Therefore, total Fe cannot be used as a criteria to di fferentiate between the Fe-deficient and non-deficient plants. On the other hand, active Fe tended to decrease with the increase in the degr ee of chlorosis. The ratio of active to total Fe was calculated and wa s found to be closely correlated with the degree of chlorosis. This cl early illustrates the failure of plant analysis for total Fe and the e ffectiveness of active Fe and/or the ratio of active to total Fe for d iagnosing Fe chlorosis.