Characterization of a Pyrenophora teres f. maculata Mapping Population Reveals the Complexity of Virulence in the Spot Form Net Blotch-Barley Interaction

Pyrenophora teres f. maculata is a major pathogen of barley worldwide, however, little is known about the virulence underlying this disease. To gain insight into pathogen virulence, a mapping population of 118 progeny was developed using a cross between P. teres f. maculata isolates FGOB10Ptm-1 (North Dakota) and SG1 (Australia). The population was phenotyped using 13 diverse barley lines including lines from the world barley core collection assembled by the Triticeae Coordinated Agriculture Project (T-CAP). Lines selected from the collection demonstrate a differential reaction to the parental isolates. The North Dakota isolate exhibited significantly higher virulence on nine of the barley lines while the Australian isolate had higher virulence on four of the lines. Genotyping was done using a two-enzyme restriction associated DNA (RAD) GBS approach developed for the Ion Torrent PGM. A SNP pipeline identified a total of 983 informative SNP markers that were distributed across 16 linkage groups generating a total map size of 1650 cM. QTL analysis identified more than 25 genomic regions associated with P. teres f. maculata virulence; QTL associated with individual barley lines were identified. The variation in virulence QTL between barley lines and the high number of genomic regions associated with virulence shows a high level of complexity in pathogen virulence and therefore it is likely that a similar level of complexity will be found in host resistance/susceptibility.