Genomic Regions Associated with Virulence in Pyrenophora teres f. teres Identified by Genome-Wide Association Analysis and Bi-parental Mapping

Net form net blotch (NFNB), caused by the fungal pathogen Pyrenophora teres f. teres (Ptt), is an important foliar disease present in all barley producing regions of the world. This fungus is a hemibiotrophic and heterothallic ascomycete where sexual recombination can lead to changes in disease expression in the host. Knowledge of the genetic architecture and genes involved in virulence is vital to increase the durability of NFNB resistance in barley cultivars. We used a genome-wide association mapping approach to characterise Ptt genomic regions associated with virulence in Australian barley cultivars. One-hundred and eighty-eight Ptt isolates collected across five Australian states were genotyped using DArTseq™ markers and phenotyped across twenty different barley genotypes. Association mapping identified fourteen different genomic regions associated with virulence with the majority located on Ptt chromosomes 3 and 5 and one each present on chromosomes 1, 6 and 9. Four of the regions identified were confirmed by quantitative trait loci (QTL) mapping. The QTL regions are discussed in the context of their genomic architecture, together with examination of their gene contents which identified 20 predicted effectors. The number of QTL shown in this study at the population level clearly illustrates a complex genetic basis of Ptt virulence compared to pure necrotrophs such as the wheat pathogens Parastagonospora nodorum and P. tritici-repentis