THE VIRULENCE GENES FREQUENCY IN BARLEY POWDERY MILDEW POPULATION (ERYSIPHE-GRAMINIS, F-SP HORDEI) IN SLOVAKIA AND NEIGHBORING COUNTRIES IN 1993

In 1993 we found the virulence genes frequency in barley powdery mildew population in Slovakia and neighbouring countries. In all observed regions there was uniform presence of virulence genes Ml-a(6), Ml-a(12) and Ml-k resistance genes. However, at the other genes we found significant differences according regions. We suppose that differences are caused by different collections of growing barley varieties in various regions. In Slovakia in pathogen population there are isolates with virulence genes which have at present no direct host variety in the collection of growing barley varieties. Their presence can be caused by migration of pathogen conidia from other regions and association with other virulence genes in complex pathotypes. High frequency of virulence genes was found against Ml-a(6), Ml-a7+?, Ml-a(12) and Ml-k and in Austria also Ml-g resistance genes. In Slovakia and Czech Republic there is the highest virulence against Ml-a(13) resistance gene. In Hungary there is considerable lower virulence. In Slovakia and Hungary a high virulence was found against Ml-La resistance gene. The lowest virulence was observed against Ml-a(3) resistance gene in all regions (except Hungary). From 459 analyzed barley powdery mildew isolates no one virulent was found against ml-o resistance gene (the variety Alexis).