Rice blast is one of the most devastating diseases, particularly panicle blast leads to significant yield losses. Utilization of panicle blast resistance genes is one of the effective ways to control this disease. However, genetic resources with panicle blast resistance are rare. The objective of this study was to identify the role of OsEXOIII-1, a previously identified candidate gene, in Pigm-mediated panicle blast resistance in rice. There were two main haplotypes in rice germplasm, with OsEXOIII-1^Hap1, the product of the resistant haplotype, binding more strongly to PiBP1 than OsEXOIII-1^Hap2. OsEXOIII-1/PiBP1 positively regulates Pigm-mediated panicle blast resistance by regulating expression of PR1 subfamily genes. OsEXOIII could be a target for breeding panicle blast-resistant cultivars.

The development of resistant varieties and hybrid combinations has been the most effective and economical strategy to control blast disease caused by Magnaporthe oryzae. However, the distribution of major R genes and blast resistance characterization in hybrid rice parents has not been well investigated, resulting in their limited use in hybrid rice blast-resistance breeding. In the present study, 88 elite indica hybrid rice parental lines were evaluated with 30 isolates of M. oryzae collected from the main planting area of indica hybrid rice in China and were characterized for the presence of 11 major resistance genes using molecular markers. The pathogenicity assays showed that four types of hybrid rice parent line showed some resistance to M. oryzae. However, the proportions of highly resistant lines and the mean resistance frequency (RF) varied among the four types, with resistance in decreasing order shown by three-line restorer lines, three-line maintainer lines, two-line sterile lines, and two-line restorer lines. All 88 hybrid rice parental lines carried more than one R gene, but none carried the R genes Pi1 and Pi2. Although Pid3 and Pi9 were present only in three-line restorer lines and Pigm only in three-line maintainer lines, the remaining six R genes (Pib, Pid2, Pi5, Pia, Pi54, and Pita) were present in the four types of hybrid rice parent with significantly different distribution frequencies. The correlation between R genes and resistance reactions was investigated. The results are expected to provide useful information for rational utilization of major R genes in hybrid rice breeding programs.