Development of a Differential Set for the Race analysis of Puccinia hordei Otth.

Investigations for the race analysis of P. hordei (location Cologne, W.-Germany) showed, that most of the resistant genotypes in the International differential set with Pa₁ to Pa₈ were ineffective for that purpose. Out of 80 selected barley genotypes with different degree of resistance against the field-collection RG 1975 hosts with a strongly differentiating effect were chosen. This was done using three parameters: mean resistance x?w, its standard deviation x?w and the range z. They were calculated from evaluating the reaction types of 80 barley genotypes infected with 116 single-pustule lines of barley brown rust. Eight hosts with strongly differentiating reactions towards the 116 rust lines were composed into a differential set, which could characterize the heterogeneity of the Cologne P. hordei-population essentially better and more precisely than the International differential set.