Kuan-Lin Lo, Yi-Nian Chen, Min-Yu Chiang, Mei-Chun Chen, Jerome P Panibe , Chung-Chun Chiu , Lu-Wei Liu, Liang-Jwu Chen, Chun-Wei Chen, Wen-Hsiung Li, Chang-Sheng Wang

Rice (N Y) 2022 Jan 10;15(1):2.  doi: 10.1186/s12284-021-00547-z.

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.

See: https://pubmed.ncbi.nlm.nih.gov/35006368/

Figure 1: Mapping of the blast resistance genes in SA0169 using linkage analysis and QTL-seq. a Log of odds (LOD) plot by the Haley-Knott regression method. Solid line indicates the LOD threshold of 3.64. b Δ(SNP‐index) plot of chromosome 6 with statistical confidence intervals under the null hypothesis of no QTLs (green lines, P < 0.05; orange lines, P < 0.01). Blue dots, ∆ SNP‐index. Red lines, the average Δ(SNP‐index) in a 1 Mb region using a 10 kb sliding window. Pink shaded region indicates the candidate region of blast resistance using the QTL-seq strategy (Pi169-6(t)). Bottom, LOD plot of blast resistance by linkage mapping. c Δ(SNP‐index) plot of chromosome 11. Pink shaded region indicates the candidate region of blast resistance (Pi169-11(t))