A new finely mapped Oryza australiensis-derived QTL in rice confers resistance to brown planthopper

• We finely map a major BPH resistance QTL qBph4.2 to a 300 kb region in rice.
• We develop a high efficient system of marker-assisted backcrossing (MABC) for qBph4.2.
• We highly improve BPH resistance of two cultivars (ZS97 and 9311) through MABC.

Brown planthopper (BPH) is the most destructive pest of rice in Asia. The BPH resistance in the introgression line IR65482-17-511-5-7 (IR65482-17) is derived from the wild rice species Oryza australiensis. An F2:3 population from a cross between Zhenshan 97 (ZS97) and IR65482-17 was used to map three quantitative trait loci (QTLs) for seedling resistance and feeding rate to BPH. The loci were distributed on chromosomes 2, 4 and 12. The QTL qBph4.2 on chromosome 4 had the largest effect, and contributed 36–44% of the phenotypic variance with a LOD score of 19–29. To validate the effect of qBph4.2, two near-isogenic lines (NILs) containing the qBph4.2 locus in the backgrounds of ZS97 and 9311 were developed by marker-assisted backcrossing (MABC). BPH bioassays showed that lines homozygous for the IR65482-17 allele (NIL +) of qBph4.2 tented to have significantly higher seedling resistance to BPH than those homozygous for the ZS97 or 9311 alleles (NIL −). Resistance was associated with a lower feeding rate by the insect. qBph4.2 was delimited to a ~ 300 kb (0.04 cM) region flanked by markers RM261 and S1, and co-segregating with XC4-27. This study will facilitate map-based cloning and marker-assisted selection of the gene, and permits further studies of gene function and resistance mechanisms in rice: BPH interaction.