Constructing linkage maps of brown planthopper resistance genes Bph1, bph2, and Bph9 on rice chromosome 12.

Genetic analysis of three brown planthopper (BPH) resistance genes—Bph1, bph2, and Bph9—was conducted using the segregating populations derived from crosses of Tsukushibare with Norin-PL3 (a Bph1 introgression line), Norin-PL4 (a bph2 introgression line), or Pokkali (donor of Bph9). BPH bioassays showed that Bph1 and Bph9 were single dominant genes, but a recessive gene, bph2, reportedly also behaved as a dominant gene. Restriction fragment length polymorphism, amplified fragment length polymorphism, and random amplified polymorphic DNA markers were selected by bulk segregant analysis. Bph1 was mapped on the long arm of chromosome 12, with the closest marker being at 3.1 cM. bph2 and Bph9 were mapped at the regions proximal to the Bph1 locus. Within 3.2 cM covering the bph2 locus, nine AFLP markers were identified, one of which showed complete cosegregation. bph2 was located within the 1.0-cM distance between two other flanking markers. Together with the known Bph10(t) locus from Oryza australiensis, our results revealed the clustering of four functional BPH resistance genes on the long arm of rice chromosome 12. The construction of a fine linkage map of bph2 should help mapbased cloning and marker-assisted pyramiding with other BPH resistance genes.