Dynamics of changes in the races and virulence of wheat powdery mildew in Hungary between 1971 and 1999

Important microevolutional processes have taken place in the wheatpowdery mildew population over the last thirty years. There has been aconsiderable change in the race composition of the pathogen populationand in the prevalent races. Of the 78 races identified, only eleven have`lived' for more than 15 years. Many races were only isolated in one ortwo years. The number of virulence genes rose from 2.03 in 1973 to 5.63in 1993. On the basis of race composition and virulence the wheatpowdery mildew population between 1971 and 1999 can be divided intofour distinct groups. A large proportion of the powdery mildew isolates arevirulent to most resistance genes. Complete resistance is provided byresistance genes Pm4a (Khapli) and partial resistance by Pm2 + Mld (Halle st. 13471), Pm4b+ (TP 315/2) and Pm1 + 2 + 9 (Normandie). The majority of cultivated varieties carry theresistance gene Pm8 due to the presence of the 1B/1R translocation.