Molecular marker analysis of European Setosphaeria turcica populations

Setosphaeria turcica is the causal agent of northern corn leaf blight, a foliar maize disease of worldwide economic importance. In Europe, its severity increases. To investigate the pathogen's population-genetic structure in central Europe, a total of 80 isolates was sampled in Germany, Switzerland, France, Austria, and Hungary and investigated with 52 random amplified polymorphic DNA (RAPD) markers. The mating type of the isolates was determined in testcrosses. Among the 73 isolates from maize there were 26 different RAPD haplotypes. All isolates with identical haplotype are considered clonemates. The haplotype shared by most members was represented by 22 isolates from Germany, Switzerland, and France, indicating high fitness and substantial migration. Only a single clone had members in both southeastern Austria and southwestern Switzerland, suggesting that the Alps constitute a major barrier for this pathogen. Several haplotypes differed by only one or two RAPD bands from the predominant haplotype and may have arisen by mutation. Few other clonal lineages were detected. The evolution of some haplotypes could not be explained by mutation alone. Sexual recombination may rarely occur. In population samples from Germany, Switzerland, and France, mating type MAT2 was predominating, while most isolates from Austria and Hungary had MAT1. Seven isolates from Johnson grass (Sorghum halepense), an alternative host of S. turcica, were clonemates and very different in RAPD haplotypes from all isolates collected from maize.