First Report of Alternaria Black Spot of Rose Caused by Alternaria alternata in Pakistan

In Pakistan, roses are commercially valuable as ornamentals and for perfumes essential oils, rose syrup, and herbal tea. During 2015-2016, circular to oval black spots (2 to 3 mm in diameter) were observed on roses in the cities of Islamabad and Rawalpindi. A total of 35 symptomatic leaves were surface sterilized with 1% sodium hypochlorite for 2 min and then rinsed three times with sterile distilled water. Excised segments (3 mm2) of surface sterilized tissue were transferred to potato dextrose agar (PDA) and incubated at 25 ± 2°C. After 5 days, white colonies developed from 25 samples and later turned black or golden brown. The conidia were borne singly or in short chains and were obpyriform to obclavate, 10-40 x 6.2-17.60 µm with 0 to 3 longitudinal and 2 to 6 transverse septa. The morphological characters matched those of Alternaria alternata (Fr.) Keissl (Simmons 2007). For confirmation of pathogenicity, three asymptomatic mature rose leaves were surface sterilized with 1% sodium hypochlorite and the...