Changes in virulence frequencies and higher fitness of simple pathotypes in the czech population of blumeria graminis f.Sp. hordei

Abstract

The employment of specific genes, which determine host resistance to avirulent pathotypes of the pathogen, is not recommended for protecting barley against powdery mildew (Blumeria graminis f.sp. hordei). However, most barley varieties still possess specific resistance genes to this pathogen. The effectiveness of such resistances was determined by assessing virulence frequency using randomly collected Czech population samples of 521 pathogen isolates from the air tested on 29 barley differential varieties over a four-year period. Most virulence frequencies did not show major changes, but the frequencies on the winter cv. Laverda and the spring cv. Kangoo greatly increased. The highest virulence frequency in all four years was on the resistance Ru2 in Kompolti 4. The period of sampling the air population and associated changes in the proportion of spores that developed on spring and winter varieties with different resistances are one of causes of the changes in virulence frequencies. It was also found out that the virulence complexity of pathotypes with the frequency > 1 was markedly lower than the complexity of pathotypes with the frequency of 1. This could indicate the higher fitness of pathotypes with fewer virulences.