Mapping and Characterization of Pyrenophora teres f. maculata Virulence Provides Needed Information for Breeding Durable Spot Form Net Blotch Resistance

Spot form net blotch caused by the necrotrophic fungal pathogen Pyrenophora teres f. maculata is a major pathogen of barley worldwide. Even with the ever increasing effect on world barley production, little is known about the pathogen virulence underlying this disease. The pathogen likely produces several necrotrophic effectors that elicit necrotrophic effector triggered susceptibility (NETS) in the host. To gain insight into the virulence of P. teres f. maculata, a mapping population was developed using a cross between P. teres f. maculata isolates FGOB10ptm (North Dakota) and SG1 (Australia) to derive 118 progeny. The population was phenotyped using 13 diverse barley lines including lines from the world barley core collection put together by the Triticeae Coordinated Agriculture Project. Lines selected from collection demonstrated differential reaction to the selected parental isolates. Genotyping was done using a two-enzyme restriction associated DNA (RAD) GBS approach developed for Ion Torrent next generation sequencing technology. A SNP calling pipeline utilizing Burrows-Wheeler-Aligner and SAMtools identified a total of 983 informative SNP markers. These SNP markers were used to develop the first genetic map of a P. teres f. maculata population. The 983 markers were distributed across 17 linkage groups generating a total map size of 1679.2 cM. Employing the phenotypic data and genetic map, quantitative trait loci (QTL) associated with P. teres f. maculata virulence were identified. Preliminary results show multiple genomic regions demonstrating the complexity of P. teres f. maculata virulence as well as virulence loci that are barley genotype specific.