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. 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.
ITS sequences determined for 53 Erysiphe specimens on Syringa and Ligustrum collected in Europe, East Asia, and North and South America were divided into two ITS groups, S and K types. Phylogenetic analysis showed that these two ITS types do not share a common ancestor and form separate clades. The K type on Ligustrum was identified as Erysiphe ligustri based on the three-dimensional branching pattern of appendages. Morphological observations showed that there are some morphological differences-pigmentation of appendages and number of ascospores per ascus-between the S and K types on Syringa. Based on these morphological observations, the S and K types on Syringa were identified as E. syringae and E. syringae-japonicae, respectively. The recent abundant production of chasmothecia by lilac powdery mildew in Europe was caused by E. syringaejaponicae introduced from East Asia. DNA sequence analyses of the rDNA ITS region and the 28S rDNA, tub2, CYP51, and Chs1 genes did not support an interspecific hybrid origin for E. syringae-japonicae. Haplotype analysis suggested that E. syringae originated in North America and independently migrated to East Asia and Europe/South America.
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