Characterization of the Complex Net Form Net Blotch Susceptibility Locus Harboring Multiple Molecular Interactions on Barley Chromosome 6H

Pyrenophora teres f. teres (Ptt) is a necrotrophic fungal pathogen and the causal agent of the destructive foliar disease net form net blotch in barley. Resistance/susceptibility to NFNB has often mapped to a common locus in the centromeric region of barley chromosome 6H. Barley cultivars Rika and Kombar were found to be susceptible to Ptt isolates 6A and 15A, respectively, and the susceptibility exists in repulsion at the centromeric 6H locus. Fine mapping using SNP markers developed from barley orthologs of syntenic Brachypodium genes and 2976 recombinant gametes derived from a Rika/Kombar cross delimited the major effect Susceptibility to Pyrenophora teres 1 (Spt1) locus to ~0.29 cM between markers rpt-M8 and rpt-M32. Additionally, two minor effect quantitative trait loci (QTL), Spt2 and Spt3, were identified within the Spt1 region and within an ~0.06 cM region, respectively. A candidate Spt1 gene, a LRR-receptor like gene, was identified in barley cultivar Morex within the newly delimited region. Allele sequencing from Rika, Kombar, and Morex identified a predicted protein consisting of a conserved C-terminal LRR, diverged N-terminus, and predicted transmembrane domain. Allele analysis of globally diverse barley lines shows a strong correlation between the presence of a Rika, Kombar, or Morex allele and susceptibility to Ptt isolates 6A, 15A, and TA5/TD10, respectively, indicating the possibility of Spt1 being a functional multi-allelic susceptibility gene. Spt3 was physically mapped to an ~105 kb region on two overlapping BAC clones containing a single phosphoenolpyruvate carboxykinase. Validation will be attempted through BSMV-VIGS, development of transformants, and mutagenesis.