Allele mining for blast-resistance gene at Pi5 locus in rice

Abstract

Rice plays a crucial role in global food security, serving as a staple for more than half of the world's population. Rice blast, caused by the fungus Magnaporthe oryzae, is one of the most devastating fungal diseases, resulting in substantial economic losses in terms of rice yield and grain quality. The resistance provided by individual blast resistance genes tends to become ineffective within a few years of extensive agricultural use due to the rapid evolution of the fungus. Therefore, continuous efforts in resistance breeding in rice are required to enrich the pool of new resistance genes and alleles. A large-scale screening of new blast resistance alleles was conducted across 2000 rice accessions from major rice-producing areas in China. Field trials were employed in two rice uniform blast nurseries located in Enshi and Yichang. Approximately 153 rice accessions showed at least moderate resistance to the rice blast. Sequence-based allele mining was used to identify the allelic variants of major rice blast resistance genes at the Pi5 locus of chromosome 9. Six novel alleles were identified from 64 accessions. Field tests at five locations, including Enshi, Yichang, Lvtian, Taojiang, and Yaan, and greenhouse inoculation using 33 blast strains from Hubei, Hunan, Guangzhou, and Sichuan, were employed to verify the resistance of these six alleles. Three near-isogenic lines (types 2, 4, and 6) were constructed and inoculated with 31 blast isolates from Heilongjiang to evaluate their blast resistance. Furthermore, bulk segregant analysis was used to confirm that Pi5-type2 and Pi5-type6 are dominant alleles in the analyzed populations. These novel alleles expand the allelic series, enriching the genetic resources for rice blast resistance breeding programs, especially in the north of China. Furthermore, they provide valuable insights into the molecular interactions between rice and rice blast.