Potato (Solanum tuberosum L.) is the fourth most important food crop in the world after wheat, rice and corn (Naraghi et al. 2010). Approximately, 4000 ha potato is cultivated in Kurdistan Province, west of Iran every year. In 2014, potatoes (cv. Agria) showing leaf spot and blight symptoms on leaves was observed in Ghorveh, Kurdistan Province. Disease symptoms were observed on more than 2-3% of plants in the potato fields in three different villages (Dizaj, Hajiabad and Kazemabad). Leaves and tubers of infected plants were collected and transferred to laboratory. Isolation was carried out for both leaves and tubers on Potato Dextrose Agar (PDA), at 25oC under 12 h photoperiod for 7 days. Isolates were purified by transferring a single spore onto PDA by dilution plate techniques. Based on morphological characteristics on Potato Carrot Agar (PCA) media, four isolates were identified as Alternaria cantlous (Simmons 2007). Colonies of the fungus on PCA media had dense growth, initially brown and changed to dark brown after 7 days. Mycelium of fungus was dark brown, smooth, hyphae branched, septata and 2-3 µm wide. Conidiophores were golden brown, simple or branched, erect, 3-4 × 60-90 µm with 5-8 genicula sporifera praebentia. Conidia ranged from 20-30 × 12-15 µm and were medium to dark brown in color, mostly spherical or ellipsoidally shaped with 3-5 transverse septa and 0-2 short longitudinal septa. To confirm morphological characterization, RNA polymerase second largest subunit (RPB2) of the representative isolate IRAN 2369C was amplified and sequenced using primers 5F2 (5′-GGGGWGAYCAGAAGAAGGC-3′) and 7cR (5′- CCCATRGCTTGYTTRCCCAT-3′) (Woudenberg et al. 2013). The resulting sequences were deposited in GenBank (KT428793). The identity of the representative isolate IRAN 2369C was confirmed by BLAST search on the GenBank database and maximum parsimony (MP) phylogenetic analysis with PAUP v4.0b10. Blast analysis of the RPB2 sequence showed high identity (99%) with the c
