Breaking genetic linkage barriers to improve brown planthopper resistance and grain yield in japonica rice.

The brown planthopper (BPH) poses a persistent threat to global rice production as one of the most devastating insect pests. Development and utilization of BPH-resistant rice cultivars are believed to be the most sustainable and eco-friendly control strategy, which has been successfully implemented in indica rice subspecies but remains underdeveloped in japonica rice. Here, we introgressed the BPH resistance gene Bph27(t) into elite japonica cultivars. Although the introgressed lines demonstrated robust BPH resistance throughout all developmental stages, they unexpectedly exhibited a brown anther phenotype accompanied by significantly reduced spikelet fertility. Histological analyses revealed that the brown anther phenotype and spikelet sterility in Bph27(t)-carrying japonica plants were likely caused by delayed tapetum degradation, leading to anther indehiscence. Furthermore, a brown anther locus, Ba1, was identified and localized to a 1.3 Mb region closely linked to Bph27(t). Genome assembly of the donor parent, Balamawee, revealed an approximately 1.1 Mb inversion in the fine-mapped region. By breaking the genetic linkage between Bph27(t) and Ba1, BPH-resistant japonica rice with high seed-setting rates was subsequently developed. The identification of Ba1 provides a new genetic resource to further explore the molecular mechanisms underlying rice anther development. Moreover, the development of novel BPH-resistant japonica germplasm lays the foundation for breeding high-yield and BPH-resistant japonica rice varieties.