RICE GENOTYPE DIFFERENCES IN NUTRIENT STATUS UNDER EXCESSIVE FERRIC-IRON CONDITIONS

To investigate the relationship between rice genotypic variation in to lerance to iron (Fe) toxicity and nutrient element status, 10 rice gen otypes with different growing performances under Fe toxicity were grow n under normal culture solution and with excessive ferrous (Fe2+)-Fe c oncentrations of 250 and 500 mg Fe2+ L-1. A close relationship was obt ained between the relative ratio of symptomatic leaf numbers to total leaf numbers (SLN/TLN) and a relative decrease in dry matter under Fe2 +-toxicity conditions. The genotypic variations in nitrogen (N), phosp horus (P), potassium (K), and magnesium (Mg) uptake were evaluated by the relative decrease in the N, P, K, and Mg content in the plants. Re markable genotypic variation in tolerance to excessive Fe2+ was observ ed. The results indicated that excessive Fe2+ reduced N, P, K, and Mg uptake. The nutrient element concentrations, however, were still highe r above deficient criteria even in severely affected plants, suggestin g that the retardation of growth may not be intirely due to the defici ency of these elements in plants at the seedling stage. Significant co rrelations were found between the genotypic variation and the decrease in N, P, K, and Mg uptake and in their tolerance to Fe2+ toxicity, wh ich suggests that the ability to maintain higher nutrient element upta ke under a Fe2+-toxic condition contributes the tolerance to Fe2+ toxi city.