Pathogenic Variation among Isolates of Pyrenophora teres, the Causal Agent of Barley Net Blotch

Isolates of Pyrenophora teres, the causal agent of net blotch of barley (Hordeum vulgare L.) has been collected from France and Syria. Their virulence spectra were evaluated using 11 barley genotypes as differential hosts. The genotypes exhibited a continuous range of response from highly susceptible to moderately resistant. A mean disease rating of 3.7 is considered as the separation point between avirulent and virulent reactions. The frequency of virulence was highest for isolates S5, R5 and S6-2 and lowest for R-ICA31 and R-HAS-6. A cluster analysis indicated that the isolates exhibited distinct differential virulence patterns and they were identified into five groups. The French isolates S5, R5 and S6-2 had a higher mean virulence and a low variance across all genotypes. None of the tested genotypes was highly resistant to all investigated isolates.