8th INTERNATIONAL WHEAT CONFERENCE

that changes in the composition of the cultivated varieties explained 60% of the changes
observed in the pathogen population.
Using the differentiating series recommended by COST Action 817, the virulence of the
wheat powdery mildew population to 18 Pm genes and gene combinations was analysed
in eight consecutive years (2001–2008). In the seedling test, none of the genes examined
was able to ensure complete resistance to powdery mildew. This was true even of the
Pm3b gene, for which only 24.7% of the isolates exhibited virulence. Less than 50% of the
isolates were able to infect differentiating varieties carrying the Pm3d (27.3%), Pm1+2+9
(41.3%) and Pm1 (48.7%) genes. In the case of varieties bearing genes Pm4a, Pm8, Pm5,
Pm3c, Pm2 and Pm6, the virulence of the powdery mildew population did not differ
significantly from the value observed for the susceptible control (100%).
The differentials carrying designated Pm genes were also sown in the field to enable virulence
data to be compared with field infection data. In the field experiment several genes
provided the wheat varieties with a good level of resistance. Variety carrying the gene
Pm3d had values not significantly different from 0. Lines bearing genes Pm3b, Pm3c,
Pm4a or Pm17 exhibited above-average infection, and even Pm8, which is still widespread
in Hungary, was unable to provide protection under field conditions.
Acknowledgements: This research was funded from the DTR_2007 Jedlik grant No.
OM188/2007.
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