Molecular evidence in support of recent migration of a powdery mildew fungus on Syringa spp. into Europe from East Asia

Abstract

A preliminary analysis demonstrated that the powdery mildew fungus infecting Syringa spp. (lilacs) in different parts of the world is divided into two groups (S‐type and K‐type) based on the nucleotide sequences of the rDNA ITS regions. In spite of the marked genetic differences (only c. 94% similarity between ITS types), fungi belonging to these two ITS groups are difficult to distinguish based on morphological characteristics. To determine their geographical distribution, ITS haplotypes were determined for a total of 139 powdery mildew specimens collected in Asia, Europe and North and South America between 1977 and 2005. Curiously, until 1990, only the S‐type was found in Europe, whilst the K‐type prevailed in East Asia. The first European specimen belonging to the K‐type was collected in Ukraine in 1991. Other European K‐type samples were collected in Lithuania and Switzerland in 2000, and in other countries after 2002. The incidence of the S‐type decreased rapidly in Europe after the 1990s. This result strongly suggests that the K‐type was introduced to Europe from East Asia in the 1990s and expanded from Eastern Europe westward, replacing the S‐type present on the European lilacs. The K‐type produces abundant chasmothecia (sexual fruiting bodies), whereas chasmothecia on the S‐type are rare in Europe and East Asia. It is likely that the recent abundant production of chasmothecia on Syringa spp. in Central Europe is explained by the migration of the K‐type to Europe.