Bridging germplasm and mechanisms: screening for resistance and decoding defense strategies against rice gall midge (Orseolia oryzae Wood-Mason) in rice.

From 4006 rice accessions, this study identified 20 highly resistant accessions against the rice gall midge and revealed that their resistance is closely associated with morphological and physiological traits, thus providing critical and diverse resources and insights for resistance breeding. The Asian rice gall midge (RGM, Orseolia oryzae Wood-Mason) is a major rice pest causing substantial yield losses. Its larvae parasitize basal meristematic tissues of rice shoots, inducing hollow, tube‑like galls known as "silver shoots." Host plant resistance represents the most viable and economical strategy for managing this pest. However, resistant germplasm resources remain limited, and the mechanisms underlying resistance are still poorly characterized. In this study, we evaluated 4,006 natural rice accessions for RGM resistance using a bulk seedling screening assay. Based on resistance levels, the accessions were classified as follows: 20 (0.5%) highly resistant, 48 (1.2%) resistant, 78 (1.9%) moderately resistant, 451 (11.3%) susceptible, and 3,409 (85.1%) highly susceptible. Despite their high resistance, most of the 20 highly resistant accessions showed considerable genetic diversity and undesirable agronomic traits. Analysis of resistance mechanisms revealed that 11 accessions exhibited both antixenosis and antibiosis, while four and five displayed only antixenosis or only antibiosis, respectively. Thirteen of the highly resistant accessions resisted RGM through a non‑hypersensitive pathway. Morphological rice seedling traits at the three-leaf stage, particularly the angle and sheath height of the second leaf, were significantly correlated with RGM oviposition preference, as validated using natural populations and an F2 segregating population, suggesting a role in antixenosis. Physiological comparisons showed markedly higher total phenolic and hemicellulose contents in shoots of resistant accessions than in susceptible ones. This study significantly expands the genetic resources for breeding RGM‑resistant rice and advances understanding of rice-RGM interactions, providing valuable insights and tools for crop improvement.