Fine mapping and pyramiding of brown planthopper resistance genes QBph3 and QBph4 in an introgression line from wild rice O. officinalis

The brown planthopper (Nilaparvata lugens Stal; BPH) has become the most destructive insect pest in rice-producing areas. Finding, characterizing and pyramiding BPH resistance genes have become increasingly recognized as an efficient approach to cope with the frequent infestations by BPH. Introgression line IR02W101 is derived from the wild rice Oryza officinalis. Using a BC1F2:3 population from a cross between Zhenshan 97 and IR02W101, we firstly mapped QBph3 on the long arm of chromosome 3, and QBph4 on short arm of chromosome 4, explaining 28 and 35 % of the variation in BPH response, respectively. We further used two BC2F2:3 populations to fine-map QBph3 to a 47-kb region co-segregating with marker c3-14, and QBph4 to a 200-kb region. Furthermore, we developed eight near-iso-genic lines and four pyramided lines (PLs) containing both or either of QBph3 and QBph4 with Bph14 and Bph15 in the backgrounds of Zhenshan 97 and 9311, by marker-assisted backcrossing (MABC). The BPH bioassay showed that the PL-QBph3/QBph4 was the most resistant of the lines. The fine mapping and pyramiding of QBph3 and QBph4 will facilitate map-based cloning of these genes, which can be used immediately in hybrid breeding and production.