Strawberry viruses mostly occur as multiple infections and leading to exhibition of symptoms and significant yield losses. To investigate mixed infections of several strawberry viruses of different genera, a total of 42 strawberry leaf samples were collected with viral symptoms from the west (Kurdistan Province) and north (Qazvin, Guilan, Golestan, and Mazandaran Provinces) of Iran. Total RNA of the samples was extracted by silica method and complementary DNA (cDNA) was synthesized using random hexamer primers. cDNA of each sample then subjected to polymerase chain reaction (PCR) for detection several important strawberry viruses among Strawberry crinkle virus (SCV; Genus Cytorhabdovirus), Strawberry mottle virus (SMoV; Genus Sadwavirus), Strawberry pallidosis-associated virus (SPaV; Genus Crinivirus), strawberry crinivirus 3 (SCrV-3; Genus Crinivirus), and strawberry crinivirus 4 (SCrV-4; Genus Crinivirus) using specific primers for each virus. PCR results further confirmed by sequencing at least one amplified fragment for each virus. The results showed wide distribution of strawberry viruses in Iran. All samples from the west of Iran were infected by at least one virus species and only three samples from the north of Iran did not test positive for any of these viruses. Based on the tested samples, SCV was found in the highest incidence (78%), followed by SCrV-3 (57%), SMoV (52%), SPaV (33%), and SCrV-4 (10%). Collectively, single infection was observed in only eight samples, with multiple infections of two, three, and four virus species in various combinations were detected in 13, 11, and seven samples, respectively. No samples were infected by all five viruses, and no correlation was found between the type of viruses in the mixed infections and symptoms observed. Extensive cultivation of strawberries in Iran and the lack of any commercially resistant strawberry cultivars against strawberry viruses, constitute an emerging threat to strawberry production.
