Abstract:

With the combination of advanced backcrossing and artificial directional selection for yield under drought stresses at rain-fed lowland and upland, sixty-five BC₂ introgression lines (ILs) with two relatively uniformed genetic backgrounds (IR64 and Teqing) and two donors with relatively good drought tolerances (BG300 and BG304) were developed and assayed with SSR makers. Using this set of materials, SBR was identified by artificial inoculations of R. solani from fields at Philippines belonging to the AG-1 group. Lengths of all lesions (TLL) from 5 randomly selected tillers per hill were measured. Analysis of genetic overlap between SBR and DT was carried out at two levels. First is the phenotypic analysis for SBR of the DT ILs from directional selection, in which the recurrent parents (RP) were used as the control and the ILs behaved better in yield were selected under the stress when the RP were almost killed and had not seed. The Teqing DT ILs tended to be decreased in SBR due to the selective introgression comparing with their RP, which showed medium resistance (MR) in our test; while the IR64 DT ILs tended to be increased in SBR comparing with IR64, which represented medium susceptibility (MS) in the same test. This kind of purge caused by directional selection indicated the possible correlation of DT with SBR in this set of ILs at the phenotypic level. The sencond is the genomic region overlaps detected by ANOVA and excessive introgression. Besides the underestimates by ANOVA of SBR loci, a total of six loci were found to be associated with SBR in DT ILs and five of them matched the 7 of the 26 loci reported previously by other researchers. Among the 6 loci, QSbr10 was detected for the same donor alleles in both backgrounds, while QSbr6 was detected for different donor alleles in different backgrounds; three loci (QSbr6, QSbr8, and QSbr10) overlaped the DT loci detected with the same ILs in our previous study.

Key words: Rice (Oryza sativa L.), Drought tolerance (DT), Sheath blight resistance (SBR), Genetic overlap, QTL