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Abstract Rice blast, one of the most destructive epidemic diseases, annually causes severe losses in grain yield worldwide. To manage blast disease, breeding resistant varieties is considered a more economic and environment-friendly strategy than chemical control. For breeding new resistant varieties, natural germplasms with broad-spectrum resistance are valuable resistant donors, but the number is limited. Therefore, artificially induced mutants are an important resource for identifying new broad-spectrum resistant (R) genes/loci. To pursue this approach, we focused on a broad-spectrum blast resistant rice mutant line SA0169, which was previously selected from a sodium azide induced mutation pool of TNG67, an elite japonica variety. We found that SA0169 was completely resistant against the 187 recently collected blast isolates and displayed durable resistance for almost 20 years. Linkage mapping and QTL-seq analysis indicated that a 1.16-Mb region on chromosome 6 (Pi169-6(t)) and a 2.37-Mb region on chromosome 11 (Pi169-11(t)) conferred the blast resistance in SA0169. Sequence analysis and genomic editing study revealed 2 and 7 candidate R genes in Pi169-6(t) and Pi169-11(t), respectively. With the assistance of mapping results, six blast and bacterial blight double resistant lines, which carried Pi169-6(t) and/or Pi169-11(t), were established. The complementation of Pi169-6(t) and Pi169-11(t), like SA0169, showed complete resistance to all tested isolates, suggesting that the combined effects of these two genomic regions largely confer the broad-spectrum resistance of SA0169. The sodium azide induced mutant SA0169 showed broad-spectrum and durable blast resistance. The broad resistance spectrum of SA0169 is contributed by the combined effects of two R regions, Pi169-6(t) and Pi169-11(t). Our study increases the understanding of the genetic basis of the broad-spectrum blast resistance induced by sodium azide mutagenesis, and lays a foundation for breeding new rice varieties with durable resistance against the blast pathogen.

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Magnaporthe oryzae (Anamorph: Pyricularia oryzae), the causal agent of rice blast disease, is the major pathogen that reduces the yield of rice worldwide. Melanin biosynthesis inhibitors (MBIs) and strobilurins (QoIs) are common fungicides used to control the disease. One hundred and three M. oryzae isolates from different rice-production areas in Taiwan were evaluated for their molecular phylogeny and sensitivity to MBI and QoI fungicides. Molecular phylogenetic analysis showed that all M. oryzae isolates could be classified into nine genetic groups (A-I) based on the DNA polymorphism amplified by CNS1/MP primers. Predominant ones are groups A (72 isolates) and B (15 isolates). Fungicide tests showed that M. oryzae isolates were sensitive to MBIs (carpropamid and tricyclazole) and less sensitive to QoIs (kresoxim-methyl and azoxystrobin). Amplifying the cytochrome b (cyt b) gene revealed that isolates with low sensitivity to QoIs did not correspond with mutation at codon 129 or 143 in the cyt b gene. [ABSTRACT FROM AUTHOR]