Rice cropped under waterlogged conditions may present symptoms of nutritional disorders similar to those caused by iron (Fe) toxicity. The symptoms do not occur in the same intensity in all cultivars and are more frequent in modern cultivars. The aim of our study was to evaluate the plant capacity of oxidizing reduced iron (Fe2+)on the root surface in green house conditions, comparing two rice cultivars (BR IRGA 409 and EPAGRI 108) with different degrees of susceptibility to iron toxicity and two different concentrations of soluble iron. The completely randomized experimental design consisted in a factorial of 2² with an extra treatment in which the plants were maintained in nutritive solution only. In order to obtain solutions with different of Fe2+ concentrations, two kinds of soils (Gleissolo Lamico and Planossolo Hidromorfico) were used. The plants were initially cultivated in complete nutrient solution during 30 days and afterwards in solutions extracted from waterlogged soils during 24 hours. The plant oxidative capacity was estimated based on the amounts of Fe compounds on the root surface. BR IRGA 409 expressed the same oxidative capacity as the EPAGRI cultivar, therefore oxidation capacity was not the differenciating variable between the two cultivars in relation to high or low sensitivity to iron toxicity. The Planossolo solution, because of its higher Fe2+ concentration (280 mg L-1), allowed a higher accumulation of Fe oxides on roots than the less concentrated Gleyssolo solution(118 mg L-1). The oxide plaque on roots of the EPAGRI 108 cultivar, tolerant to iron toxicity, was less active in P adsorption than that of the BR IRGA 409 cultivar, considered sensitive.
Oriza sativa; iron toxicity; oxide plaque; phosphorus adsorption