Of environmental stresses in rice production, tolerance to excess of soluble iron is known to show a clear genetic difference. The severest abiotic stress in the lowlands is iron toxicity in west Africa's lateritic soils. It has been shown that genetic tolerance to iron toxicity can contribute significantly to rice production in toxic soils. 6 We started a program to search for genetic markers for this tolerance. Initially, the testing method had to be improved. An improved screening method was developed on the basis of solution culture. Then, a search for RAPD markers which might be linked to the tolerance was started. To obtain stable PCR products as selection markers, the sequence of RAPD markers had to be determined as site-tagged sequences (STS), for which a set of new primers could be developed. This approach enabled us to identify, with a
high level of precision and reproducibility, a monogenic segregation in the tolerance, and can be a standard in any selection for highly variable tolerance to environmental stress.
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