Biochemical indicators to diagnose iron nutritional status of olive (Olea europaea L.)

• The severity of chlorosis symptoms in olive trees had no relationship with leaf Fe concentration. • Leaf activity of APX and POX were not useful indicators to diagnosis Fe status of olive. • The chlorophyll a concentration in > 85 % of chlorotic leaves was <0.6 mg g -1 FW. • In > 96 % of chlorotic leaves, activity of CAT was less than 1.5 Unit mg protein -1 . • CAT activity and chlorophyll a concentration can successfully be used for diagnosing Fe status in olive trees. While iron (Fe) chlorosis undesirably affects the growth and yield of olive ( Olea europaea L.) in calcareous soils, no proper indicator is available to diagnose Fe nutritional status of plant. This two-year study aimed to find out a valid biochemical indicator most related to the plant Fe status. Eight olive orchards with different soil characteristics were selected in various regions of Isfahan province, Iran. In each orchard, 6 uniform trees with similar size, age, and performance were selected, half of the trees received 0.150 kg Fe in the form of FeEDDHA (6%) and thereafter exhibited no or slight chlorosis symptoms while the other half did not receive Fe and showed severe chlorosis symptoms. The results did not confirm any relationship between Fe concentration in the leaves and severity of chlorosis symptoms. Neither phosphorus (P) concentration nor the activity of ascorbate peroxidase (APX) and peroxide (POX) in plant leaves were useful indicators to diagnose Fe deficiency in olive trees. Leaf concentration of carotenoids and chlorophyll b in the leaves was also poor indicators to separate chlorotic and green trees. In contrast, concentration of chlorophyll a and activity of catalase (CAT) in the leaves were strongly correlated with the severity of chlorosis. The chlorophyll a concentration in more than 85% of chlorotic leaves was less than 0.6 mg g -1 FW. Additionally, in more than 96% of chlorotic leaves, the leaf activity of CAT was less than 1.5 Unit mg protein -1 . According to the results, activity of CAT and concentration of chlorophyll a can successfully be used as proper indicators to diagnose Fe status in olive trees.