Using DNA to Understand Basil Downy Mildew Population

Basil downy mildew (Peronospora belbahrii) is a biotrophic oomycete pathogen which infects basil plants globally. Since its arrival in the United States in 2007, basil downy mildew has devastated both commercial and home-grown basil crops, due to its ability to spread rapidly, and persist in greenhouse environments. In recent years, we have observed P. belbahrii isolates which can infect different basil resistant cultivars, indicating a higher degree of genetic diversity in the population than previously predicted. To provide an overview of population genetic drive, the internal transcribed spacer (ITS) rDNA regions of three isolates of interest were amplified, sequenced, and compared to a previously assembled data set. These data were combined with a cultivar panel, where pathogenicity of each isolate was compared across ten basil cultivars. Our phenotypic observations were reflected in the phylogenetic relationships between the three pathogen isolates, indicating a connection between pathogen race and ability to overcome cultivar resistance mechanisms. Understanding how these genomic changes are reflected in pathogenicity will allow future research groups to more effectively design resistant basil cultivars and provide a quick way to identify which P. belbahrii strain is present in a specific crop.