Résumé
IR64 x Azucena DH population was used for mapping QTLs of resistance to Rice Yellow Mottle Virus (RYMV), the most damaging rice pest in irrigated fields of West Africa. Resistance was studied first using a serological test (ELISA) to estimate virus concentration in the plants and second at field level, through symptoms scoring and impact of the disease on morphological traits. Resistance appeared to be under a polygenic determinism. Seven QTLs of resistance have been evidenced on chromosome 1, 2, 4, 8, 9 and 12. For all the QTLs, allele conferring resistance was brought by the resistant parent, Azucena. Three QTLs of resistance were colocalized with some QTLs controlling plant height, tillering ability and cycle duration, noted on healthy plants. Especially, QTL of chromosome 1 was explaining a large part of resistance at field level and in ELISA and was colocalized with the semi-dwarf gene sd-1 coming from the susceptible parent IR64. QTL of chromosome 12 has already been described in this population and in the population IRAT177 x Apura. Mapping of this QTL was refined using a near isogenic approach based on successive backcross on IR64. It was now mapped in a 3 cM confidence interval near the RFLP marker RG869, where no QTL for morphology was detected. A great proportion of phenotypic variation for resistance was assumed by an interaction of the QTL of chromosome 12 and a chromosomal fragment on chromosome 7. NILs for these two QTLs are on the way to introgress partial resistance of upland rice in IR64. (Texte intégral)