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Abstract
The pathogenicity of 137 isolates of Blumeria graminis f. sp. hordei (progenies of single colonies) originating from five locations in New Zealand was analysed using a differential set of 15 near‐isogenic lines ('Pallas'). The isolates belonged to 14 pathotypes, five of which comprised a sub‐population obtained only from the greenhouse. The pathotypes exhibited four to seven virulences, and all possessed Vg, Vra, and Vh. They were also avirulent for resistance genes Mla3, Mla6, [Mla7 Mla(No3)], Mla9, Mlal3, and Mlkl, but differed by the presence (or absence) of virulences Va1, Va12, VLa, Vat, V(Ru2), and Vp1. Forty‐nine isolates (35.8% of the total) belonged to the predominant pathotype ‘14055’. There were considerable differences in the composition of individual sub‐populations, which could indicate that the vegetative (conidial) stage is less important for survival and distribution of the pathogen in New Zealand. Direct selection of the pathogen population on host varieties is apparently slower in New Zealand than in Central Europe. Little or no gene flow occurs between the New Zealand and Australian populations.
