Pathogenicity of Blumeria graminis f. sp hordei in New Zealand in 1997

The pathogenicity of 137 isolates of Blumeria graminis f sp. hordei (progen ies 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 subpopulatio n obtained only from the greenhouse. The pathotypes exhibited four to seven virulences, and all possessed Vg, Vra, and Vh. They were also avirulent fo r resistance genes Mla3, Mla6, [Mla7 Mla(No3)], Mla9, Mla13, and Mlk1, 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 pre dominant pathotype '14055'. There were considerable differences in the comp osition of individual subpopulations, which could indicate that the vegetat ive (conidial) stage is less important for survival and distribution of the pathogen in New Zealand. Direct selection of the pathogen population on ho st varieties is apparently slower in New Zealand than in Central Europe. Li ttle or no gene flow occurs between the New Zealand and Australian populati ons.