First report of Alternaria alternariacida causing potato leaf blight in the Far East, Russia

Early blight of potato (Solanum tuberosum) is caused by Alternaria species and occurs annually in major potato producing regions of Russia. Diseased potato leaves displaying early blight symptoms were collected in July 2016 from a commercial field in Primorsky Krai, Russia (43.8242° N, 131.6219° E). The disease incidence was 30 to 40%. The initial symptoms appeared as typical early blight symptoms with a dark brown margin and diffused chlorosis on the leaf blade. Symptomatic leaves from different plants were randomly collected to isolate axenic cultures of the causal agents. Infected leaves were placed in wet chambers (moist filter papers in Petri dishes), and incubated at 25°C, 16 h/8 h dark/light photoperiod for 2-4 d. Single conidia were transferred to potato dextrose agar (PDA, Crous et al. 2009) in Petri dishes and incubated at 25°C for 7 d in the dark. Colonies were white-olivaceous, reverse side - olivaceous. Isolates were transferred onto potato carrot agar (PCA, Crous et al. 2009) and incubated at 22°C under a 16 h/8 h dark/light photoperiod for 7 d to stimulate sporulation. Most isolates (85%) were identified as A. protenta according to the morphological characteristics and molecular data, although one isolate showed sporulation that was somewhat atypical, having a smaller (especially narrower or more slender) conidia. Conidiophores were long, erect, and 65 to 100 µm × 5 to 6 µm in size. Conidia were solitary, long-ovoid in body with six to eight transverse septa, and 85 to 100 µm× 6 to 10 µm in size. Conidial beaks were filamentous, 110 to 200 µm × 2 to 5 µm in size. Genomic DNA was extracted from cultured isolates using the CTAB-chloroform extraction method (Griffith & Shaw 1998), and five gene regions including the internal transcribed spacer (ITS) region, translation elongation factor 1-alpha (tef1), RNA polymerase second largest subunit (rpb2), Alternaria major allergen (Alt a 1) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes were amplified with the primer pairs ITS1/ITS4, EF1-728F/EF1-986R, RPB2-5F2/FRPB2-7cR, Alt-for/Alt-rev, and gpd1/gpd2 respectively (Woudenberg et al. 2014). PCR products were Sanger sequenced. All sequences for isolate A16PrPL21 were identical to isolate CBS 105.51; (accession nos.: ITS, KJ718105; tef1, KJ718454; rpb2, KJ718279; Alt a 1, KJ718625; gpd KJ717959) of A. alternariacida Woudenb. & Crous. ITS, tef1, rpb2, Alt a 1 and gpd sequences were deposited in GenBank under the accessions OM348531, MN580518,