Developing near-isogenic lines of IR64 introgressed with QTLs for deeper and thicker roots through marker-aided selection

A well-developed root system is an important trait contributing to drought resistance in rice. Preliminary work allowed us to map QTLs involved in the control of several root traits in a doubled-haploid population of rice derived from the cross IR64 x Azucena. We are now developing near-isogenic lines of IR64 introgressed with the major QTLs. Four segments on chromosomes 1, 2, 7, and 9 were initially targeted for single QTL selection. Four doubled-haploid lines with the proper allelic combination at the targeted segments and less than 50% Azucena alleles in the rest of the genome were chosen as donors. These lines were backcrossed on IR64 up to the BC3F1 generation and then selfed. Marker-aided selection for the target segments was performed from BC1F1 up to BC3F2. All he selected BC3F2 progenies carried the donor alleles for at least one target region. Plants carrying two target segments were also identified. Phenotypic variation for several nonarget traits was observed in the BC3F2 plants, suggesting the presence of genetic drag during introgression. A background survey of the rest of the genome indicated that the BC3F2 plants had a very small portion of Azucena alleles in the non-target regions, close to the expected ~3%. Crosses were made between BC3F2 plants carrying different target donor segments to remove possible genetic drag and pyramid different target QTLs. (Résumé d'auteur