Nutrient culture media with agar is effective for early and rapid screening of iron toxicity tolerance in rice

The breeding for iron toxicity tolerant rice needs an effective, efficient, and reliable screening method. The study was aimed to evaluate the best method for screening iron tolerant genotypes at the seedling stage in the greenhouse. Two rice genotypes, Mahsuri (tolerant) and IR64 (sensitive) were grown in three modified media solutions namely, Yoshida-conventional solution (YCS), Yoshida with etylenediamintetraacetic acid (1:2) (YES), and Yoshida with 0.2% agar (YAS). Three levels of iron were tested to observe the severity of their leaf bronzing score (LBS). The optimized solution in the greenhouse was then evaluated using 24 rice genotypes. Using the same genotypes interrelationship, the LBS in the greenhouse with grain yield and its attributes was validated under acute and moderate Fe toxicity in the field. The results showed that the optimized media culture was YAS with 400 mg L^-1 of FeSO₄. This media had more stable pH and redox potential, it could maintain sufficient Fe²⁺ supply over 10 days, and it could discriminate of LBS between tolerant and sensitive genotypes. Evaluation using the optimized media solution showed that there was a significant variation among genotypes in shoot dry weight and a significant correlation of relative reduction of shoot dry weight with LBS. The LBS in the greenhouse was correlated with LBS in acute iron stress in the field (r=0.673**) and the grain yield (r= -0.618**). This study has proven that YAS culture media can be used as early identification of iron toxicity tolerant genotypes for supporting breeding programs.