Regional phenotypic diversity of Puccinia triticina and wheat host resistance in western Europe, 1995

Pathogenicity data from surveys of Puccinia triticina (formerly P. recondit a f. sp. tritici) conducted in western Europe in 1995 were analysed to comp are the structure of regional populations of the pathogen. Many of the popu lations differed in phenotypic diversity and pathotypic composition, even t hough they occurred within a single epidemiological unit, suggesting that l ocal factors may influence the establishment and propagation of individual pathotypes in the regional populations. Neighbouring regions were more simi lar than distant regions, and all regions shared at least one pathotype, ex cept populations in northern Italy and Scotland. A high degree of similarit y was found between populations in northern France and Great Britain, provi ding strong evidence of free movement of inoculum between these regions. Re sistance genes were postulated for a selection of 91 wheat cultivars, repre senting those most commonly grown in western Europe in 1995. Thirteen culti vars lacked detectable seedling resistance genes and the remaining 78 posse ssed from one to three resistance genes; those detected were Lr1, Lr3a, Lr1 0, Lr13, Lr14a, Lr17b, Lr20, Lr26 and Lr37. The most commonly detected resi stance gene was Lr13, which was present singly or in combination with other resistance genes in 48 cultivars (53%). The gene Lr14a was detected in 18 cultivars, Lr26 was present in 16 cultivars. The role of host selection in the composition of the regional populations of P. triticina in western Euro pe in 1995 was difficult to assess on the basis of the results obtained, si nce virulence data were not available for Lr13 and Lr14a.