Background The rice gall midge (RGM, Orseolia oryzae, Wood-Mason), an important stem-feeding pest worldwide, has caused serious production losses over the past decades. Rice production practices indicate that the most reliable method for managing RGM is the deployment of cultivars that incorporate host resistance. However, the conventional phenotypic screening method of rice resistance to RGM suggested by the International Rice Research Institute (IRRI) has been used for approximately 30 years, and only 12 rice varieties/lines (including controls) can be evaluated in one tray. It is not suitable for high-throughput phenotyping of rice germplasm. Moreover, a suitable method to prepare samples for molecular biological studies of rice resistance against RGM is imperative with the rapid development of modern molecular techniques. Results The proper density of seedlings/RGM was determined for four seeding arrangements. A high-throughput phenotyping method (HTPM) for 60 lines/varieties infested with 36 female RGM adults in one tray, as described by method 4–3 (seeded 60 lines/varieties), was developed and verified using mutant screening. Furthermore, one RGM resistance gene flanked by markers 12RM28346 and 12RM28739 on chromosome 12 was simultaneously detected using method 2–2 (seeded 30 lines/varieties in one tray) treated with 24 RGM and analyzed using conventional and simplified grading systems. Genetic analysis of the RGM resistance gene was confirmed using a method identical to that suggested by IRRI. Finally, one bucket with 24 seedlings treated with at least five female RGM adults was efficacious and could offer adequate samples for insect development observation or molecular biological studies. Conclusion A highly efficient and reliable procedure for evaluation of resistance in rice to RGM was developed and improved, and was verified through mutant screening, gene mapping, genetic analysis, and insect growth and development observations.

Every year, rice planthoppers (main brown planthopper, BPH, Nilaparvata lugens Stål), one of the most important pests in rice production, cause huge yield losses worldwide. The identification of resistance genes and exploration of insect resistance mechanisms are some of the most fundamental and effective methods to manage the pest. Here, the aspartic protease (AP) gene OsAP79 was transcriptionally expressed in all organs tested, particularly in the roots at the adult stage. The knockout of OsAP79 impaired rice resistance to BPH, whereas overexpression (OE) of OsAP79 improved rice resistance by increasing plant survival rates, and reducing BPH weight gain and honeydew excretion. Observation of the transverse section of rice shoots indicated that OE lines of OsAP79 can significantly enhance sclerenchyma layer thickness. Meanwhile, a significantly longer or shorter root was detected in the knockout or OE lines, respectively, which was positively correlated with the indole acetic acid (IAA) content. Hormone measurement and metabolomic analysis suggested that IAA biosynthesis, the citric acid cycle, and glycolysis biosynthesis contributed greatly the OsAP79-induced resistance of rice against BPH. Collectively, OsAP79 was continuously induced to express and enhance BPH resistance by reducing the IAA content, which restricts root growth and increases shoot sclerenchyma layer thickness. This study demonstrates the previously unappreciated importance of the AP gene in rice for combating piercing-sucking insect herbivores.