Exploring resistance mechanisms and identifying QTLs for brown planthopper in tropical and subtropical rice (Oryza sativa L.) germplasm.

Key message: A total of 4006 tropical and subtropical rice germplasms were screened for brown planthopper resistance, and the resistance mechanisms of 63 highly resistant accessions were characterized. This led to the designation of three novel resistance QTLs: Bph47, Bph48, and Bph49. The brown planthopper (BPH) is a significant piercing-sucking pest of rice plants that causes widespread destruction globally. Discovering new germplasms and genes for BPH resistance is essential for enhancing genetic diversity in rice breeding. In this study, 4006 rice accessions from tropical and subtropical regions were screened for BPH resistance at the seedling stage, and 63 accessions with high-resistant were identified. Of these, 59 accessions exhibited high resistance to BPH at the adult stage. The 63 accessions displayed widespread variation in key agronomic traits, though most were generally unsatisfactory. Assessments of antixenosis, antibiosis, and tolerance indicated diverse resistance mechanisms in the 63 accessions, with the majority (39/63) demonstrating both antixenosis and antibiosis. Microscopic observations and physiological assessments revealed significant differences in vascular bundle structure, fiber content, and activity of defense-related enzymes between the 63 high-resistance and 27 susceptible ones. Furthermore, correlation analysis highlighted a substantial positive relationship between BPH resistance and parameters such as rice trypsin inhibitor (RTI) levels and width of the sclerenchyma layer (WSL). Genetic analysis of F_2:3 segregating populations from four resistant accessions crossed with the susceptible rice variety 9311 identified three novel major-effect quantitative-trait loci (QTLs) located on chromosome 1L (690 kb and 1.84 Mb) and 5S (295 kb). This study significantly enriched the BPH-resistant germplasm sources and genes, highlighting the varied resistance mechanisms of rice against BPH.