Substitution mapping and characterization of brown planthopper resistance genes from traditional rice cultivar 'Rathu Heenati' (Oryza sativa L.)

The brown planthopper (BPH; Nilaparvata lugens St & aring;l) is a devastating pest that causes severe rice yield losses in Asia. Introducing multiple BPH resistance genes into rice cultivars is an effective and sustainable way to mitigate yield losses. A traditional rice cultivar, 'Rathu Heenati', has durable BPH resistance due to multiple resistance genes (including BPH3 and BPH17) and quantitative trait loci (QTLs). However, these genes have not been used in Japanese rice breeding owing to limited genetic information. To identify markers tightly linked to BPH3 and BPH17 introgressed into the 'Sagabiyori' (susceptible) genetic background, we performed substitution mapping. BPH3 was delimited between RM3132 and RM589 on chromosome 6, and BPH17 between RM16493 and RM16531 on chromosome 4. We also performed QTL analysis to identify additional BPH resistance genes from 'Rathu Heenati' and detected a QTL, denoted as qBPH3.1, on chromo- some 3. The effect of pyramiding BPH3 and BPH17 was significantly greater against virulent BPH popula- tions than that of either gene alone. The combination of BPH3, BPH17 and qBPH3.1 from 'Rathu Heenati' might be facilitated to improve commercial Japanese cultivars with more robust BPH resistance.