Barley mildew in Europe: population biology and host resistance

Abstract

Isolates of the barley mildew pathogen from the air spora over a large part of Europe and from fields of variety mixtures, were tested for virulence against 12 host resistance alleles . Subsamples were tested for their response to triadimenol fungicide and analyzed for 10 DNA loci using RAPD markers and PCR . There was a large range of haplotypes spread over Europe ; irregularity in the distribution was probably due mainly to non-uniform use of the corresponding host resistances and fungicides . A large range of variation was also detectable within individual fields . Positive gametic disequilibria distorted the distribution of virulence alleles among haplotypes and reduced the number of haplotypes detectable in the sample . Analysis of the spread of the newly selected Val3 allele into different European sub-populations indicated that gene flow throughout the population may be rapid for alleles that have a selective advantage .Fungicide resistance was widespread in areas known for intensive use of fungicides for mildew control . Four classes of fungicide response were detectable and particular virulence haplotypes were found to be characteristic for each class .Variety mixtures used in the former German Democratic Republic (GDR) reduced mildew infection, and thus fungicide use, during the years 1984-1991 despite the limited variation in host resistance among the mixtures . A tendency for complex pathogen races to increase in mixture crops was reversed by the large-scale re-introduction of fungicides for mildew control in 1991 . The mixture strategy appeared to be more successful than using the same resistance alleles in pure monoculture or combining them in a single host genotype .

Changes in virulence frequencies and higher fitness of simple pathotypes in the Czech population of Blumeria graminis f.sp. hordei

“…The widespread use of these resistances was reflected in the structure of the pathogen population. This situation can be compared with the use of Ru in Czech varieties when only 4-7 years had elapsed from the detection of the first pathotype virulent to Ru until epidemics broke out on barley cultivars with this resistance in the Czech Republic and Europe (Brückner 1982;Wolfe et al 1992). Experience with the resistance Ru and examples of the rapid increase in the frequency of virulences that overcame Ro and Lv demonstrate the short-term effectiveness of using single specific resistances in widely grown monoculture crops.…”

Adaptation of Blumeria graminis f.sp. hordei to barley resistance genes in the Czech Republic in 1971-2000

“…Considering the variety resistance, adaptation of the pathogen population to gene Mla13 was the most important change within the entire host-pathogen system. Owing to subsequent emigration of virulent pathotypes (Dreiseitl 2001b), it became an event of European importance (Wolfe et al 1992). The mentioned process from development of virulent individuals due to mutation (Brückner 1982) through intensive direct selection of virulent pathotypes to total breakdown of resistance conditioned by gene Mla13 (Dreiseitl and Pařízek 2003) took place in the domestic territory.…”

Pathogenicity ofBlumeria graminisf. sp.hordeiin New Zealand in 1997

“…It is particularly prevalent in cooler and more humid regions of temperate climates, such as Central and Northern Europe. Most of the European continent is a uniform epidemiological region where a change in the composition of a local population gradually affects the population across the whole land mass (Wolfe et al 1992).…”