THE VIRULENCE GENES FREQUENCY IN BARLEY POWDERY MILDEW POPULATION (ERYSIPHE-GRAMINIS, F-SP HORDEI) IN SLOVAKIA AND NEIGHBORING COUNTRIES IN1993

In 1993 we found the virulence genes frequency in barley powdery milde w population in Slovakia and neighbouring countries. In all observed r egions 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 signi ficant 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 v irulence genes which have at present no direct host variety in the col lection of growing barley varieties. Their presence can be caused by m igration of pathogen conidia from other regions and association with o ther virulence genes in complex pathotypes. High frequency of virulenc e genes was found against Ml-a(6), Ml-a7+?, Ml-a(12) and Ml-k and in A ustria also Ml-g resistance genes. In Slovakia and Czech Republic ther e is the highest virulence against Ml-a(13) resistance gene. In Hungar y there is considerable lower virulence. In Slovakia and Hungary a hig h virulence was found against Ml-La resistance gene. The lowest virule nce was observed against Ml-a(3) resistance gene in all regions (excep t Hungary). From 459 analyzed barley powdery mildew isolates no one vi rulent was found against ml-o resistance gene (the variety Alexis).