Basal or partial resistance has been considered race-non-specific and broad-spectrum. Therefore, the identification of genes or quantitative trait loci (QTLs) conferring basal resistance and germplasm containing them is of significance in breeding crops with durable resistance. In this study, we performed a bulked segregant analysis coupled with whole-genome sequencing (BSA-seq) to identify QTLs controlling basal resistance to blast disease in an F₂ population derived from two rice varieties, 02428 and LiXinGeng (LXG), which differ significantly in basal resistance to rice blast. Four candidate QTLs, qBBR-4, qBBR-7, qBBR-8, and qBBR-11, were mapped on chromosomes 4, 7, 8, and 11, respectively. Allelic and genotypic association analyses identified a novel haplotype of the durable blast resistance gene pi21 carrying double deletions of 30 bp and 33 bp in 02428 (pi21-2428) as a candidate gene of qBBR-4. We further assessed haplotypes of Pi21 in 325 rice accessions, and identified 11 haplotypes among the accessions, of which eight were novel types. While the resistant pi21 gene was found only in japonica before, three Chinese indica varieties, ShuHui881, Yong4, and ZhengDa4Hao, were detected carrying the resistant pi21-2428 allele. The pi21-2428 allele and pi21-2428-containing rice germplasm, thus, provide valuable resources for breeding rice varieties, especially indica rice varieties, with durable resistance to blast disease. Our results also lay the foundation for further identification and functional characterization of the other three QTLs to better understand the molecular mechanisms underlying rice basal resistance to blast disease.

Grain size and grain weight are important determinants for grain yield. In this study, we identify a novel OsMAPK5–OsWRKY72 module that negatively regulates grain length and grain weight in rice. We found that loss‐of‐function of OsMAPK5 leads to larger cell size of the rice spikelet hulls and a significant increase in both grain length and grain weight in an indica variety Minghui 86 (MH86). OsMAPK5 interacts with OsMAPKK3/4/5 and OsWRKY72 and phosphorylates OsWRKY72 at T86 and S88. Similar to the osmapk5 MH86 mutants, the oswrky72 knockout MH86 mutants exhibited larger size of spikelet hull cells and increased grain length and grain weight, whereas the OsWRKY72‐overexpression MH86 plants showed opposite phenotypes. OsWRKY72 targets the W‐box motifs in the promoter of OsARF6, an auxin response factor involved in auxin signaling. Dual‐luciferase reporter assays demonstrated that OsWRKY72 activates OsARF6 expression. The activation effect of the phosphorylation‐mimicking OsWRKY72^T86D/S88D on OsARF6 expression was significantly enhanced, whereas the effects of the OsWRKY72 phosphorylation‐null mutants were significantly reduced. In addition, auxin levels in young panicles of the osmapk5 and oswrky72 mutants were significantly higher than that in the wild‐type MH86. Collectively, our study uncovered novel connections of the OsMAPKK3/4/5‐OsMAPK5‐mediated MAPK signaling, OsWRKY72‐mediated transcription regulation, and OsARF6‐mediated auxin signaling pathways in regulating grain length and grain weight in an indica‐type rice, providing promising targets for molecular breeding of rice varieties with high yield and quality.