Analytical methods for evaluating iron chlorosis in peach trees

Abstract

This study was implemented to determine the appropriate methods to be used in evaluation of iron (Fe) chlorosis in peach trees. For this purpose, three peach orchards having trees various visual chlorosis ratings were selected, and the leaf samples were collected during a 2-year period. The leaf samples were collected from two different positions in the annual shoots: 1) 5(th) 6(th), and 7(th) leaves in midpoint position of annual shoots and 2) extremity leaves of annual shoots. The leaf samples were only taken from the trees at 3 stages in the first year of the experiment to determine most convenient date of sampling. The experiment had 3 chlorosis categories (green, slightly chlorotic, and severely chlorotic) in the first year and 5 chlorosis categories in the second year (green, slightly chlorotic, slightly green, chlorotic, and severely chlorotic) with 3 replicates in each of the orchards. One M HCl, 1.5% o-phenanthroline, 0.5 M oxalic acid, and 0.1 M HCl methods in the fresh leaf samples, 1 M HCl, 0.5 M oxalic acid, 0.1 M HCl, and total Fe methods in oven-dried leaves were used for Fe analysis. The data were statistically analyzed by analysis of variance (ANOVA) and the least significant difference (LSD) values were calculated at the 5% level. According to the results obtained from the experiment, 1 M HCl and 1.5% o-phenanthroline in the fresh leaves and 1 M HCl in oven-dried leaves were well related to visual chlorosis ratings and chlorophyll content of the leaves as compared with other methods. The 1 M HCl method seemed to be the method of choice for producing a suitable index of Fe status of plants due to lower cost of analysis and ease in handling dry samples. Concentration of Fe determined by this method from green leaves at the midpoint position was generally greater than or equal to 30 mg kg(-1), which may be accepted as the critical index value for Fe in peach trees. Active Fe in the midpoint leaves was markedly and significantly higher than extremity leaves. To sample midpoint leaves may be recommended in determination of active Fe. There was no evidence to sample leaves on a certain date. This might have resulted from the wide range of sampling interval.