Ferric chelate reductase activity as screening index for selecting iron chlorosis resistance of Apple rootstocks

For precise evaluation of the sensitivity of some apple rootstocks to iron stress, an study with a factoreal approach was established based on a complete randomized design with 18 treatments and three replications. Experimental treatments included rootstocks in 6 levels (M9, M26, M7, M25, MM106, MM111) and iron was chosen in three levels(Half strength Hoagland solution as control, Half strength Hoagland without iron, Half strength Hoagland with Bicarbonate). Apple rootstocks were planted in 20 liter pots containing Perlite. Before beginning the experiment, the pots were supplied with half strength Hoagland solution for 2.5 months. After this period, the abovementioned treatments were applied on the rootstocks. Drainage pH was measured 5 times during the experiment. Root ferric chelate reductase activity (FCR) in separated roots and in the intact plant with connected roots was calculated. Then, plants were separated into shoots and roots in the laboratory. Ferric chelate reductase activity, shoot growth, dry and fresh weight of leaf and root, swelling of root tip, leaf chlorophyll (Chl) concentration and iron concentration of leaf and root were also measured. According to the achieved results, M9, M7 and M25 rootstocks in comparison with M26, MM106 and MM111, showed lower leaf chlorosis. Root Ferric chelate reductase activity for M9, M7 and M25 rootstocks treated with 2µM Fe was higher than other rootstocks. The rootstock M9 in this treatment increased 4.3 times in comparison to the control and the MM106 rootstock in 10 mM sodium bicarbonate treatment had the lowest FCR activity compared to the control. In addition to the FCR increase in M9, M7 and M25 rootstocks, they had more effect in the rhizosphere pH decrease than other rootstocks. Biomass indicator (root/shoot dry weight) in rootstocks of M9, M7 and M25 showed larger values. According to the result of this experiment, due to meaningful correlation between the measurement method of FCR with excised roots and chlorophyll index, this method is a suitable approach for screening of apple rootstocks with iron chlorosis in comparison with FCR measurement with intact plant.