Identification of Resistance Sources Effective Against the Barley Spot Form Net Blotch Pathogen Pyrenophora teres f. maculata

Spot form net blotch (SFNB) caused by Pyrenophora teres f. maculata is a major foliar disease of barley worldwide. SFNB epidemics have recently been observed in major barley producing countries including the United States, Canada, Australia, Denmark, Norway and South Africa. These recent epidemics suggest that the local barley cultivars are not resistant and that virulence of the pathogen populations may have changed. A greenhouse experiment was performed to identify sources of resistance effective against diverse isolates of P. teres f. maculatacollected from around the world. A total of 2062 world barley core collection lines were phenotyped using four diverse isolates of the pathogen collected in the US, New Zealand, Australia, and Denmark. Screening for seedling resistance was performed based on a 1-5 disease reaction scale, where 1 is resistant, and 5 is susceptible. Significant differences were identified between each isolate for virulence across the world barley core collection, with the US isolate showing the highest average level of virulence. Average disease reaction types were plotted for each isolate and each resembled a bell shaped curve, indicating that few lines were either highly resistant or highly susceptible. Only 3% of the barley lines had an average disease reaction score of less than 2 when infected with the US isolate, indicating that resistance is rare. These resistant lines will be used to generate mapping populations and for germplasm development. Future research will involve the characterization of host resistance, pathogen virulence and the host-pathogen interaction associated with SFNB of barley.