First report of Alternaria leaf spot on cilantro (Coriandrum sativum) caused by Alternaria dauci in the United States

Cilantro (Coriandrum sativum), widely used in different types of cuisine worldwide, is an annual herb in the family Apiaceae, which contains over 3,000 species including parsley, celery, and carrot. In January 2017, small brown spots with a white center were observed on leaves of cilantro in a plantation in Homestead, FL. Approximately 15% of the plants in the field were infested. Small pieces (5 mm2) of the leaves containing both healthy and diseased tissues were excised, surface sterilized with 70% ethanol for 15 s, rinsed in sterilized water, followed by 5 min in 0.5% NaClO, and a final rinse in sterile water. The surface sterilized tissue was transferred to PDA (Potato dextrose agar) plates and incubated at 370C. In about 5 days, dark greenish fungal colonies were consistently grown from the tissue on PDA. The purified culture did not produce conidia on PDA, but it did on water agar after one week under a 24 h photoperiod at room temperature. The conidia were dark brown, obclavate with long tails, hav...