REGULAR ARTICLE Maintaining elevated Fe 2+ concentration in solution culture for the development of a rapid and repeatable screening technique for iron toxicity tolerance in rice (Oryza sativa L.) Venus Elec & Celsa A. Quimio & Rhulyx Mendoza & Andres Godwin C. Sajise & Sarah E. J. Beebout & Glenn B. Gregorio & Rakesh Kumar Singh Received: 24 December 2012 / Accepted: 17 April 2013 # Springer Science+Business Media Dordrecht 2013 Abstract Background and aims Iron toxicity decreases rice (Oryza sativa) grain yield especially in acid soils after flooding. Our aim was to establish a high-throughput screening technique using nutrient solution culture for identifying Fe-toxicity-tolerant genotypes. Methods Varying levels of Fe, pH, and chelators in Yoshida nutrient solution culture were tested to maintain sufficient Fe 2+ concentration over time to optimize the severity of Fe toxicity stress for distinguishing between a tolerant (Azucena) and sensitive (IR64) genotype. The optimized solution was tested on 20 diverse genotypes in the greenhouse, with measurement of leaf bronzing scores and plant growth characteristics at the seedling stage. The same 20 genotypes were grown to maturity in a field with natural Fe toxicity stress, with measurement of seedling-stage leaf bronzing scores and grain yield to determine their inter-relationship. Results Optimized nutrient solution conditions were 300 mg L -1 Fe supplied as Fe 2+ at pH 4.0 with a 1:2 molar ratio of Fe:EDTA, which maintained suffi- cient Fe 2+ stress over 5 days. The highest correlation of nutrient solution phenotypic data with field grain yield was found with leaf bronzing scores at 4 weeks, with a Pearson r of 0.628 for simple association and a Spearman corrected r of 0.610 for rank association (P < 0.01) using 20 diverse rice genotypes with proven Fe toxicity tolerance reaction. The Leaf bronzing scores at 4 weeks in nutrient culture solution were also found highly correlated with LBS under natural field stress after 8 weeks that had highest correlation with grain yield under stress. Conclusion This culture solution-based standardized screening technique can be used in plant breeding programs as a high-throughput technique to identify genotypes tolerant to Fe toxicity. Keywords Rice . Fe 2+ concentration . pH . EDTA . Iron toxicity . Screening technique Abbreviations EDDHA Ethylenediamine (2-hydroxyphenylacetic) acid EDTA Ethylenediamine tetra-acetic acid Plant Soil DOI 10.1007/s11104-013-1739-4 Responsible Editor: Hans Lambers. Electronic supplementary material The online version of this article (doi:10.1007/s11104-013-1739-4) contains supplementary material, which is available to authorized users. V. Elec : R. Mendoza : A. G. C. Sajise : S. E. J. Beebout : G. B. Gregorio : R. K. Singh (*) International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines e-mail: r.k.singh@irri.org C. A. Quimio Crop Science Cluster, College of Agriculture, University of the Philippines at Los Baños, Los Baños, Philippines