Comparision of the methods for evaluating iron chlorosis resistance in different apple scion/ rootstock combinations

Lime induced iron chlorosis is one of the important problems of fruit trees, especially apple, in calcareous soils. This disorder affects many fruit trees in these areas, each year. The purpose of this study was to determine a suitable method for evaluation of apple rootstocks and cultivars against iron stress. A factorial experiment based on Randomized Complete Block Design with 18 treatments and 3 replications was performed. Treatments included cultivars (Golab Kohanz, Red Delicious and Golden Delicious), rootstock at 6 levels (M9, M26, M7, M25, MM106, MM111) and iron stress at three levels (2 µM iron, 90 µM iron with and without 10 mM sodium bicarbonate). The treatments were applied to the grafted pot trees in in perlite after 8 weeks of feeding with half strength Hoagland solution. In this study, the effects of different levels of iron stress on theoretical Fe-efficiency indices and the biochemical properties of grafted combinations were evaluated. The results indicated different reactions of the cultivars and rootstocks, and thus the grafted combinations to the applied stresses. Cultivars and rootstocks showed remarkable differences in the absorption and transfer of iron, so that they can be categorized into resistant (iron efficient), sensitive (iron inefficient) and semi-sensitive ones. The method of biochemical assessment more accurately showed the differences between cultivars and rootstocks in response to iron stress, and provided an effective evaluation compared to the theoretical Fe-efficiency indices.