Genetic determinism of resistance to ferrous iron toxicity in rice

Lowland rice is often subject to iron (Fe) toxicity leading to yield losses. The most cost-effective way to address this constraint is the selection of resistant genotypes. In this thesis, the genetic determinism of rice resistance to Fe toxicity was investigated through the forward genetic approach, starting from the phenotypic evaluation of rice response to Fe toxicity to search for genetic factors associated with the observed variations among genotypes. A first analysis of the association between the phenotype of recombinant inbred lines and genotype of mapped markers allowed the detection of 24 genomic regions (QTLs) underlying resistance to Fe toxicity. Because QTL mapping largely depends on the screening environment and allelic diversity between parents, the QTL stability was checked in different ways: (1) new QTL analyses were performed using the same population but growing it in three additional environments; (2) new QTL analysis was performed in the same environment but using another population; (3) all QTLs identified were compared with QTLs found by other authors for resistance to Fe toxicity and an integrated map of all reported QTLs was constructed. Beside the QTL validation, these analyses allowed the detection of new genomic regions underlying resistance to Fe toxicity and highlighted the interest of four genomic regions. Both regions displaying more than 10 QTLs were mined for the identification of candidate genes on the basis of their known function and/or expression. Six strong candidates were sequenced in eight different cultivars and non-synonymous polymorphisms were detected for five of them. However, their implication in the control of resistance to Fe toxicity needs further investigation using reverse genetic tools. In conclusion, the forward genetic approach successfully identified relatively small and reliable genomic regions involved in the determinism of rice resistance to Fe toxicity, which can be used in marker-assisted selection. Moreover, new insights were given on the physiological mechanisms and putative candidate genes associated with this complex trait.(AGRO 3) -- UCL, 201