Plant tolerance mechanism to iron (Fe) toxicity involve complex physiological processes and depend on the genotypes. The objectives of the research were (1) to analyze growth response of several rice genotypes to Fe toxicity, and (2) to analyze the relationship between rice growth characters and tolerance mechanism to Fe toxicity. The research was conducted in 2 experiments. The 1st experiment was conducted to compare the effectiveness of three nutrient culture media (YHS, YHSA, and YFSA) to distinguish between Fe-tolerant (Mahsuri) and -sensitive (Inpara 5) genotypes in response to Fe toxicity. The 2nd experiment evaluated ten rice genotypes (IR64, IRH108, Danau Gaung, Hawara Bunar, Indragiri, Pokkali, Mahsuri, Inpara 2, Inpara 5 and Inpara 6) grown in nutrient culture media that were treated with and without 400 ppm Fe. To distinguish the tolerance mechanism of those rice genotypes to Fe toxicity, plant growth characters, leaf bronzing score (LBS), Fe content, and physiological responses were observed. The result showed that Yoshida half strength with agar 0.2% (YHSA) medium and 400 ppm FeSO4.7H2O for 10 days stress was effective and efficient nutrient culture medium to analyze growth response and tolerance mechanisms of rice to iron toxicity. The LBS-based rice responses to Fe stress was divided into 2 response groups, i.e.: early response (LBS1-LBS6) and late response (LBS7-LBS10). Fe toxicity decreased shoot and root growth characters. The Fe content in root plaque and shoot varied among genotypes. Analysis of relationship between genotypes and growth characters divided the genotypes into 3 groups of Fe-tolerance mechanism, i.e.: sensitive-includer (IR64 and Inpara 5), tolerant-includer (Danau Gaung, Inpara 6, Inpara 2, Mahsuri, and IRH108), and tolerant-excluder (Hawara Bunar, Indragiri, and Pokkali).
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