Erysiphe havrylenkoana and E-prunastri var. japonica: a new species and a new variety of Erysiphe sect. Uncinula (Erysiphaceae, Ascomycota)

A new species and a new variety of Erysiphe sect. Uncinula are described and illustrated. Erysiphe havrylenkoana is a new species found on Nothofagus alpina and N. obliqua in Argentina, and E. prunastri var. japonica is a new variety collected on Prunus maximowiczii in Japan. Erysiphe havrylenkoana differs from E. nothofagi, E. patagoniaca and E. magellanica in having unique helicoid appendages, brownish from the base to the beginning of helicoid part, spirally twisted at the center and straight or not spiral at the upper part with uncinate to circinate tip. The phylogenetic analyses of rDNA sequences clearly showed that the spiral pattern of helicoid appendages is an important morphological character to delimit species among Nothofagus powdery mildews. Erysiphe prunastri var. japonica is distinct from E. prunastri var. prunastri parasitizing hitherto Prunus species from East-Central Asia to Europe by having mainly eight asci per chasmothecium and smooth, rarely septate appendages.