Brown planthopper (BPH), a monophagous phloem feeder, consumes a large amount of photoassimilates in rice and causes wilting. A near-isogenic line ‘TNG71-Bph45’ was developed from the Oryza sativa japonica variety ‘Tainung 71 (TNG71) carrying a dominant BPH-resistance locus derived from Oryza nivara (IRGC 102165) near the centromere of chromosome 4. We compared the NIL (TNG71-Bph45) and the recurrent parent to explore how the Bph45 gene confers BPH resistance. We found that TNG71-Bph45 is less attractive to BPH at least partially because it produces less limonene. Chiral analysis revealed that the major form of limonene in both rice lines was the L-form. However, both L- and D-limonene attracted BPH when applied exogenously to TNG71-Bph45 rice. The transcript amounts of limonene synthase were significantly higher in TNG71 than in TNG71-Bph45 and were induced by BPH infestation only in the former. Introgression of the Bph45 gene into another japonica variety, Tainan 11, also resulted in a low limonene content. Moreover, several dominantly acting BPH resistance genes introduced into the BPH-sensitive IR24 line compromised its limonene-producing ability and concurrently decreased its attractiveness to BPH. These observations suggest that reducing limonene production may be a common resistance strategy against BPH in rice.

The continued emergence of weedy rice (Oryza sativa L.) in Taiwan poses serious challenges to seed purity and commercial rice cultivation, particularly under transplanting systems. These off-type individuals, often marked by a red pericarp, reduce varietal integrity and complicate seed propagation. This study evaluated the morphological variation among 117 Taiwan weedy rice (TWR) accessions and 55 control cultivars, which include 24 temperate japonica cultivars (TEJ), 24 indica cultivars, and seven U.S. weedy rice (UWR) types. Principal component analysis (PCA) showed that TWR shares vegetative traits with modern cultivars but exhibits grain morphology resembling indica landraces—indicating weak artificial selection pressure on grain traits during nursery propagation. TWR was also found to possess a suite of adaptive weedy traits, including semi-dwarfism, delayed heading, high shattering, and superior seed storability, facilitating its persistence in field conditions. These findings provide critical insights for integrated weed management and cultivar purity strategies, emphasizing the importance of certified seed use, stringent field hygiene, and disruption of weedy rice reproductive cycles.

The brown planthopper (BPH, Nilaparvata lugens) and white-backed planthopper (WBPH, Sogatella furcifera) are major rice pests, yet WBPH resistance and its overlap with BPH resistance remain poorly defined. Using the Rice Diversity Panel 1 (RDP1), screened against laboratory colonies, we mapped resistance to both pests across three panels and three models (MLM, FarmCPU, BLINK), examined leading loci with the High-Density Rice Array, and mined 3000-genome candidate-gene haplotypes. Resistance correlated weakly between pests (r = 0.26). We identified six BPH and five WBPH candidate loci, all ≥2.38 Mb from cloned Bph genes; correspondence with uncloned QTL cannot be excluded, and the WBPH chromosome 9 locus is the strongest novel candidate. Top signals did not co-locate and candidates shared most defense modules, but neither pattern exceeded chance in permutation testing, and the cross-trait genomic correlation was non-significant (r_g = 0.38, SE ≈ 0.33). These loci sit on a background of low genomic heritability; we can neither demonstrate pest-specificity nor exclude a shared polygenic background. Resistance-allele sources were subspecies-differentiated but locus-specific. This is the first parallel diversity-panel genome-wide association study of the two planthoppers and the first for WBPH host resistance. It provides positional candidates and candidate donor haplotypes as a validation-pending breeding resource.

Weedy rice (Oryza sativa L.) presents a formidable challenge in global paddy cultivation due to its morphological similarity to cultivated rice, making its eradication difficult. To address this, an integrated weed management system (IWMS) was developed and collected across various regions in Kaohsiung, Taiwan, from 2018 to 2020. This study evaluated the efficacy of the IWMS in controlling the spread of weedy rice through systematic applications in three distinct agricultural zones: Meinong Contractual (MC), Meinong Public Stock (MP), and Shanlin Public Stock (SP). The data reveal a consistent decline in weedy rice invasion with sustained implementation of the IWMS, alongside improvements in seed purity and corresponding grain quality. These enhancements not only mitigate the adverse effects on seed purity but also elevate grain quality, thereby curtailing yield losses and bolstering economic returns. Further analysis indicates that the patterns of weedy rice invasion correlate strongly with geographical and agronomic variables, such as the source of seedlings, land preparation techniques, field management, and the sharing of agricultural implements. Consequently, raising farmer awareness and providing specialized training on management strategies are crucial for effective prevention of weedy rice.