First report of downy mildew caused by Peronospora belbahrii on sweet basil (Ocimum basilicum) in Arkansas.
Basil (O. basilicum) is a specialty crop widely grown commercially and in home gardens in Arkansas, USA. In the USA, downy mildew caused by Peronospora belbahrii was first seen and reported in Florida in 2008 and has since been reported in 42 states plus the District of Columbia. In 2016, a grower in Fayetteville, Arkansas, reported downy mildew in basil to the online monitoring programme, but neither morphological nor molecular identification was conducted in Arkansas at that time. In 2017, the Arkansas Plant Health Clinic received samples of basil with necrotic leaves and wilting from three Arkansas counties (Pulaski, Sebastian, and Washington). The symptoms began on lower leaves and progressed from yellowing to complete leaf death. A gray mycelial growth was observed on the underside of the leaves. Brown lesions were also observed on the stems. Based on morphological characteristics, DNA sequence analysis and pathogenicity test, the causal agent was identified as P. belbahrii. This is thought to be the first report of downy mildew caused by P. belbahrii on sweet basil in Arkansas.