Mapping a recessive gene conferring resistance to rice yellow mottle virus

摘要

Rice yellow mottle virus (RYMV) is a serious disease of rice in Africa. Although partial resistance is found in upland rice varieties, all the irrigated and lowland rice varieties commonly grown in Africa are highly susceptible to RYMV. A few accessions of the African cultivated rice species (Oryza glaberrima) and a single variety of O. sat/Va (Gigante) display a very high resistance level similar to immunity. The genetic basis of resistance to RYMV was determined through interspecific and intraspecific crosses using Tog5681 (0. glaberrima) and Gigante as RYMV resistance donors and IR64 as the susceptible parent. The resistance was due to the presence of a single recessive gene with probably different resistance alleles in Tog5681 and Gigante. Bulked segregant analysis (BSA) was used to map the RYMV resistance gene. About 250 primer combinations were used to compare banding patterns between parental lines and bulks of susceptible or resistant (IR64 X Gigante) F_3 lines. In addition, more than 20 bands coming from one or the other parent were found to be candidates for the resistance coming from Tog5681. Mapping on the (IR64 x Gigante) F_2 population revealed an interval of 17 cM spanning the RYMV resistance locus. One of these markers was cloned and specific primers were designed. A cleaved amplified polymorphic sequence (CAPS) has been determined to characterize the Gigante and IR64 alleles. This marker was mapped on the (IR64 X Azucena) genetic linkage map and was localized on chromosome 4. PCR-based resistance markers allowed us to begin transferring the RYMV resistance gene into Bouake 189, BG90-2, and Jaya (O. sativa) varieties, which are very well adapted to African lowland conditions but are highly susceptible to RYMV. Fine mapping of theRYMV resistance locus and the construction of IR64 isolines with the two resistance genes are in progress.