RESUMEN
Hybrid genotypes can provide significant yield gains over conventional inbred varieties due to heterosis or hybrid vigor. However, hybrids can also display unintended negative attributes or phenotypes such as extreme pathogen susceptibility. The necrotrophic pathogen Pyrenophora teres f. maculata (Ptm) causes spot form net blotch, which has caused significant yield losses to barley worldwide. Here, we report on a non-transgressive hybrid susceptibility locus in barley identified between the three parental lines CI5791, Tifang and Golden Promise that are resistant to Ptm isolate 13IM.3. However, F2 progeny from CI5791 × Tifang and CI5791 × Golden Promise crosses exhibited extreme susceptibility. The susceptible phenotype segregated in a ratio of 1 resistant:1 susceptible representing a genetic segregation ratio of 1 parental (res):2 heterozygous (sus):1 parental (res) suggesting a single hybrid susceptibility locus. Genetic mapping using a total of 715 CI5791 × Tifang F2 individuals (1430 recombinant gametes) and 149 targeted SNPs delimited the hybrid susceptibility locus designated Susceptibility to Pyrenophora teres 2 (Spt2) to an ~ 198 kb region on chromosome 5H of the Morex V3 reference assembly. This single locus was independently mapped with 83 CI5791 × Golden Promise F2 individuals (166 recombinant gametes) and 180 genome wide SNPs that colocalized to the same Spt2 locus. The CI5791 genome was sequenced using PacBio Continuous Long Read technology and comparative analysis between CI5791 and the publicly available Golden Promise genome assembly determined that the delimited region contained a single high confidence Spt2 candidate gene predicted to encode a pentatricopeptide repeat-containing protein.