A Diagnostic Guide for Basil Downy Mildew

Abstract

Downy mildew, caused by the oomycete pathogen Peronospora belbahrii, is one of the most important diseases affecting sweet basil worldwide. Field- and greenhouse-grown basil may be affected, and crop losses are observed as the reduction of marketable leaves during both the production and postharvest handling stages. As an obligate biotroph, P. belbahrii cannot be cultured and maintained without live plant tissue, which may complicate efforts to diagnose and identify the causal agent. Thus, the goal of this diagnostic guide is to outline the appropriate methods required to identify basil downy mildew based on the symptoms of the disease and signs of the pathogen. Additionally, methods for pathogen identification, pathogen isolation, storage of single-sporangium cultures on live plants, and pathogenicity testing are described in detail.