Identification and Genomic Mapping of Three New Stagonospora nodorum Blotch Susceptibility Genes in Wheat

Stagonospora nodorum is a necrotrophic fungal pathogen of wheat that causes the disease Stagonospora nodorum blotch (SNB). The wheat-S. nodorum pathosystem involves pathogen-produced necrotrophic effectors (NEs) (formerly known as host-selective toxins) that are recognized by corresponding host genes to confer disease susceptibility. To date, five host gene-NE interactions have been reported in the wheat-S. nodorum system, all of which play significant roles in the development of SNB. Here, we present the identification and mapping of three additional wheat genes that confer sensitivity to different NEs produced by S. nodorum.  One NE sensitivity gene (temporarily designated Snn4B) was identified in the durum wheat variety Lebsock and mapped to the long arm of chromosome 4B in a population of doubled haploids.  Evaluation of SNB in this population indicated that the Snn4B locus explained as much as 53% of the variation demonstrating that Snn4B is a major SNB susceptibility gene. The second NE sensitivity gene (Snn6A) was identified in the hexaploid variety Opata 85 and mapped to the long arm of chromosome 6A in the ITMI population. This gene accounted for 20% of the variation in SNB development.  Finally, a third NE sensitivity gene (Snn5D) was discovered in the hexaploid landrace Chinese Spring and mapped to the long arm of chromosome 5D using chromosome deletion lines.  Further characterization, analysis, and marker development for these susceptibility genes is underway.  This research broadens our knowledge of the wheat-S. nodorum pathosystem and will lead to the efficient development of SNB resistant wheat varieties.