Development of elite breeding lines conferring Bph18 gene-derived resistance to brown planthopper (BPH) by marker-assisted selection and genome-wide background analysis in japonica rice ( Oryza sativa L.)

▶ This study investigated the integration of a novel gene, Bph18 conferring resistance to brown plant hopper (BPH) by foreground selection into an elite japonica cultivar Junambyeo susceptible to BPH and development of Bph18-derived advanced backcross progenies by background analysis using molecular markers. The main findings are the development of promising japonica breeding lines possessing desirable agronomic and grain quality traits with BPH resistance by marker-assisted backcross (MAB) breeding in a short period of time. Brown planthopper (BPH) is a serious threat to rice production. In this study, we have used the novel resistance gene Bph18 derived from Oryza australiensis and incorporated it into an elite japonica cultivar, Junambyeo, which is highly susceptible to BPH. The Bph18 gene was introduced by marker-assisted backcross (MAB) breeding into Junambyeo. The backcrossed progenies were evaluated for desirable agronomic and grain quality traits and the selection of improved breeding lines while simultaneously evaluating BPH resistance by bioassays in the greenhouse and foreground selection. Of the 26 advanced backcross breeding lines (ABL), four lines showed agronomic traits similar to those of the recurrent parent, with strong resistance to BPH. Molecular genotyping of the four ABL revealed the conversion of genotypes closely resembling the genotype of Junambyeo. The percentage of donor chromosome segments in ABL decreased from 12.3% in the BC 2 to 9.4%, 8.4% and 5.3% in BC 3, BC 4 and BC 5 generations, respectively. ABL retained small sizes of the donor chromosome segments on chromosomes 1, 2, 10, 11 and 12 but the genomes of ABL2, ABL3 and ABL4 were homosequential to the recurrent parent on chromosomes 3, 4, 5, 6, 7 and 9 without donor chromosome segment introgression. The ABL1 and ABL2 retained only some small segments of the donor genome on chromosomes 9 and 8, respectively. Fine structure analysis of the Bph18 flanking region between RM511 and RM1584 markers on chromosome 12 showed a progressive elimination of donor-derived chromosome segments from BC 2 to BC 5 generations. The percentage of O. australiensis derived chromosome segment substitution in the recurrent parent background decreased from 28% of the donor parent to 6.7%, 3.9%, 3.4% and 3.4% in BC 2, BC 3, BC 4 and BC 5 generations, respectively. However, it was revealed that the O. australiensis-derived chromosome segment (1320 kb) in ABL containing the Bph18 gene was consistently m