First report of Phyllosticta spinarum causing arborvitae foliar blight in Russia

Thuja occidentalis is a popular and widely planted tree in Russia. However, it is susceptible to arborvitae foliar blight, which can compromise the long-term health of trees in the landscape and in nursery production. Leaves with arborvitae needle blight were collected in 2019 in the foothill zone of the Republic of Adygea, and two isolates of Phyllosticta sp. were obtained. Multilocus analyses were performed with sequences of the internal transcribed spacer and 28 S rDNA of the ribosomal DNA, partial actin gene, partial RNA-polymerase II gene, and partial translation elongation factor 1-alpha. Based on phylogenetic analyses combined with morphological features the isolates were identified as Phyllosticta spinarum. Following inoculation of the original host species both isolates produced symptoms similar to those observed in naturally infected leaves. Koch's postulates were then fulfilled by re-isolating P. spinarum from the inoculated leaves. These findings represent the first confirmed detection of P. spinarum causing arborvitae needle blight in Russia.