The rice varieties IR64 and Jao Hom Nin (JHN) demonstrated a broad-spectrum resistance against the rice blast pathogens in Thailand. A genomic investigation unravelled many resistance genes residing on four genomic regions, chromosome 2 and 12 in IR64 and 1 and 11 in JHN. A cross between these varieties was made to combine resistance genes into a single genotype. Marker-assisted selection (MAS) was employed to identify F2 and F3 plants carrying a combination of four resistance QTLs in a homozygous fusion. Flanking markers RM212/RM319 and RM144/RM139 to blast resistant QTLs on chromosome 1 and 11 in JHN rice and tightly-linked markers RM208 and RM179 to blast resistant QTLs on chromosome 2 and 12 in IR64 rice variety were used for MAS. The stepwise MAS screening was brought in as a strategy to provide a cost-saving and minimum number of PCR performing to select resistant genotypes. F4 generation, lines carrying all resistant QTLs show a broader spectrum of resistance against 11 representatives of Thai blast pathogen isolates. (Résumé d'auteur