The first report of downy mildew caused by Peronospora belbahrii on sweet basil in greenhouses in the Czech Republic.
In April 2012, the first large chlorotic from the middle necrotic spots occurred gradually on leaves of pot plants of sweet basil (Ocimum basilicum) cv. Genovese in greenhouses in Central Bohemia. The characteristic gray to brown furry growth of downy mildew appeared on abaxial surfaces of leaves in the place of chlorotic spots within 3 to 4 days. The infested leaves fell off in the late stages of pathogenesis. The infestation gradually manifested itself in ever-younger plants and in July, cotyledons and possibly the first true leaves were already heavily infected and damaged and these plants rapidly died. The plant damage reached 80 to 100%, so it was necessary to stop growing the plants in the greenhouse at the end of July. The causal agent was isolated and identified as Peronospora belbahrii based on morphological characteristics, molecular investigations (PCR assay and sequence analysis) and pathogenicity test. Downy mildew on sweet basil was reported in countries in Africa, Europe, and South and North America. This is thought to be the first report of downy mildew on sweet basil in the Czech Republic.