Agrifood Research Reports 78

Barley, Hordeum vulgare L., is the most important crop in Finland based on cultivated land area. Net blotch, a disease caused by Pyrenophora teres Drech., is the most damaging disease of barley in Finland but is also important in other barley cultivating areas. The pressure to improve the economics and efficiency of agriculture has increased the need for more efficient plant protection methods. Development of durable host-plant resistance to net blotch is a promising possibility. However, deployment of disease resistant crops could initiate selection pressure on the pathogen (P. teres) population. The aim of this study was to understand the population biology of P. teres and to estimate the evolutionary potential of P. teres under selective pressure following deployment of resistance genes and application of fungicides. The study included mainly Finnish P. teres isolates, but population samples from Russia and Australia were also included. Using AFLP markers substantial genotypic variation in P. teres populations was identified among only a few clones. Differences among isolates were least within Finnish fields and significantly higher in Krasnodar, Russia. Genetic differentiation was identified among several populations from northern Europe and from Australia, and between the two forms of P. teres, spot and net type, in Australia. Differentiation among populations was also identified based on virulence (capacity to infect a particular host genotype) between Finnish and Russian populations, and based on prochloraz (fungicide) tolerance in barley fields in the Häme region in Finland. In contrast to previous surveys, the Finnish P. teres populations comprised only P. teres f. teres (net form of net blotch), which was also recovered from Russia, whereas both forms (net and spot: P. teres f. teres and P. teres f. maculata) were found within several fields in Australia. Surprisingly, both mating types were equally common in all but the Krasnodar population. This finding supported the assumptions of sexual reproduction of P. teres in those areas. In conclusion, P. teres populations are differentiated at several levels. Human assistance in dispersal of P. teres on infected barley seed might decrease the differentiation, which would increase plant protection problems caused by this pathogen. P. teres is capable of sexual reproduction in several areas. Based on these findings it is apparent that P. teres has the potential to pose more serious problems in barley cultivation if plant protection is neglected. Therefore, good