Eleven rice cultivars were studied as the tolerance to iron and aluminum toxicity using seven different levels of these elements in the nutrient solutions with and without aeration under constant temperature (30ºC ± 1ºC) and pH = 4.0. The plant tolerance was measured taking into account the primary root length and the leaf and root dry weight of 20 plants of each cultivar after 10-day-growth in the different treatment solutions. With levels of 0, 20 and 40 mg/l of Al in solutions with and without aeration and with the presence of 0.56mg/l of Fe it was verified that the cultivars IAC-164, IAC-165, IAC-47, IAC-25, IAC-435, IAC-120, Blue Bonnet and Pérola were tolerant and the cultivars IR-8, IAC-899 and IR-841 were sensitive. When it was utilized 200mg/l of Fe in aerated nutrient solution the cultivar IAC-164 showed high level of tolerance being significantly different from the cultivars IAC-435, IAC-899, Blue Bonnet, IAC-25, IR-8 and IR-841. 'IAC-164' did not differ from the cultivars IAC-120, IAC-47, IAC-165 and Pérola. In non-aerated solution with the same concentrations of iron and aluminum, the same result was obtained with the difference that 'IAC-164' did not differ from 'IAC-25'. In aerated nutrient solutions containing 400mg/l of Fe the most tolerant cultivar was IAC-164 which differed significantly only from IAC-899, IR-841 and IR-8. When non-aerated solution was used, no differences were found among the studied cultivars. 'IAC-164' presented high tolerance to Al and Fe toxicities even when it was applied 20mg/l of Al plus 200mg/l of Fe and 40mg/l of Al plus 400mg/l of Fe in the solutions. The Al and K concentrations increased and the P, Ca, Mg, Fe, Cu, Zn and Mn concentrations decreased in the leaf dry matter for all aluminum tolerant cultivars, as the aluminum concentration in solution increased from 0 to 40mg/l. When the cultivars sensitive to Al toxicity were considered increasing levels of Al in solution caused an increase in Al, Fe and P concentrations, and a decrease in the other element concentrations in the leaf dry matter. The Fe and K concentrations increased, Ca, Mg, Mn, Cu and Zn concentrations decreased and no effect in P concentration was observed in the total leaf dry matter for all cultivars, when Fe concentration in nutrient solution increased from 0 to 400mg/l in absence of Al. The results showed that the studied rice cultivars could be separated in relation to Al and Fe toxicities in nutrient solution with and without aeration, since adequate quantities of Al and Fe are provided.
iron toxicity in rice; aluminum toxicity in rice; aerated solutions; non aerated solutions; iron tolerance; iron sensitivity; aluminum tolerance; aluminum sensitivity; aluminum; iron; rice cultivars; tolerance; toxicity