Leaf Spot Caused by Alternaria spp. Is a New Disease of Grapevine

In this study, we carried out large-scale leaf spot symptom observation on vineyards in the Krasnodar Krai of Russia and determined their distribution. The incidence and severity of leaf spot were higher on the Euro-American grapevine hybrids (Bianka, Levokumskij, Avgustin, Moldova, Pervenets Magaracha, Dunavski lazur). A total of 433 isolates that belonged to the genus <i>Alternaria</i> were isolated from samples with leaf spot. Pathogenicity testing confirmed the ability of the representative isolates to cause necrosis on the grapevine. The isolates of <i>Alternaria</i> sp. were typed by the loci of internal transcribed spacer (ITS), glyceraldehyde-3-phosphate dehydrogenase (<i>gapdh</i>), Alternaria allergen a1 (<i>Alt a1</i>), β-tubulin (<i>tub</i>), and translation elongation factor (<i>tef1</i>). Isolates from grapevine causing leaf spot were shown to cluster with isolates of <i>Alternaria. alternata</i> (Fr.) Keissl. and <i>Alternaria. arborescens</i> E.G. Simmons species complex. Of the fungicides tested to inhibit <i>Alternaria</i> growth, the most effective were mixtures, such as pyrimethanil and fluopyram, cyprodinil and fludioxonil, and those that included difenoconazole. The results of the study expand our knowledge of the biodiversity of <i>Alternaria</i> sp. fungi and can be used to limit the spread of <i>Alternaria</i> leaf spot of the grapevine.