The genetic population structure of Pyrenopeziza betulicola, the causativeagent of birch leaf spot disease

Pyrenopeziza betulicola is a causative agent of leaf spot disease on birch. Within I? betulicola significant length variation (nine alleles) in 18S ri bosomal genes was observed. The level of geographic differentiation among a ll locations was moderate but statistically significant, indicating that th e spore dispersal of P. betulicola occurs mainly on a limited scale. Within one leaf, in situ analysis of a multiallelic molecular marker revealed gen etically distinct individuals in different spots, indicating that multiple colonization by I? betulicola is a common occurrence on birch leaves. Withi n one spot only one allele was found showing that the separate necrotic spo ts are usually formed by only one viable spore. Technically, the applicatio n of a specific marker combined with DGGE turned out to be a powerful metho d to study genetic diversity of fungi in situ.