Powdery mildew disease caused by Blumeria graminis f. sp. tritici is one of the most important diseases of wheat in Iran and in the world. The changes in the pathogen population cause the resistance genes to be ineffective leading to spread of the disease. Therefore, it is essential to monitor these changes for selecting suitable cutivars with effective reisistance genes for cultivation in infected regions. For this purpose, an experiment was conducted with trap nursery including 29 differential cultivars with different resistance genes for powdery mildew during 2015-2017 in Sari and Gorgan fields. In order to establish the disease, the susceptible cultivar of Bolani was used between rows and around the cultivated segment of the field. Disease assessment was perfomed based on the vertical spread of infection along the plant and the severity of the disease on the leaf. The results showed that in the whole years of experiment and infected regions, the highest frequency of virulence was observed for Pm7 and Pm3b resistance gene. No virulence was observed in any of the experimental years and infected regions for Mld + Pm2 and Pm12 resistance genes. For all years in Sari, virulence was observed for Pm3g and Pm6 (in addition to Pm 7 and Pm3b). Also, in this region, the Pm5a resistance gene was effective only in the first year, but in the following years, appeared to be susceptible. In Gorgan, no virulence was observed for Pm3d (in addition to Mld + Pm2 and Pm12). Based on these observations, because resistance genes of Mld + Pm2 and Pm12 were effective in all conditions, their use in cultivars for cultivation in regarding areas is suggested. It should also be avoided to cultivate cultivars with Pm7 and Pm3b in these areas.