Partial resistance to rice yellow mottle virus: QTL identification, genetic model, and QTL efficiency analysis after marker-assisted introgression

QTLs for rice yellow mottle virus resistance were mapped in a doubled-haploid population of rice, IR64/Azucena. Resistance was under polygenic control and 15 QTLs were detected on seven chromosomal fragments. For all the resistance QTLs detected, the favorable allele was provided by the resistant parent Azucena. Using different resistance parameters and two environments, three genomic fragments involved in resistance were pointed out. These segments were also involved in plant architecture and development. Significant correlations were observed between resistance and tillering ability. A resistance QTL involved in leaf virus content mapped on chromosome 12 (QTL12) was found to be independent of plant morphology. A search of interactions between this QTL and the rest of the genome and between this QTL and morphological traits segregating in the population showed that a complementary epistasis between QTL12 and a QTL located on chromosome 7 (QTL7) was the major genetic factor controlling the virus content. Marker-assisted selection was performed to introgress the resistance allele of QTLI2 and QTL7 from Azucena into IR64. After three cycles of marker-assisted backcrosses, the proportion of the recipient genome in the selected plant was close to 95% for the 10 noncarrier chromosomes, and the length of the donor chromosome segment surrounding the two QTLs was less than 20 cM. Evaluation of the level of resistance in BC1F3 and BC2F3 lines confirmed the relevance of the complementary epistasis genetic model proposed. (Résumé d'auteur