Pathogens on wild radish, Raphanus raphanistrum (Brassicaceae), in south-western Australia — implications for biological control

Biological control options for wild radish (Raphanus raphanistrum L.) were explored through a pathogen survey in south-western Australia, inoculation studies and a literature review. Twelve fungal species were isolated from diseased wild radish, including an undescribed species of Mycosphaerella and Hyaloperonospora parasitica, which have not been previously recorded on wild radish in Western Australia. H. parasitica was the most damaging and widespread pathogen of wild radish. Phylogenetic analysis based on the internal transcribed spacer regions of the rRNA genes showed that the H. parasitica isolates from wild radish are genetically distinct from the isolates found on Brassica species including canola. This finding opens up the possibility of developing a conservation or augmentative approach to the biological control of wild radish using H. parasitica. The possibility of using other pathogens in a biocontrol strategy is remote because of likely nontarget effects on canola. Leptosphaeria biglobosa and L. maculans were widespread pathogens of wild radish suggesting this weed may provide an inoculum source for blackleg disease on canola (Brassica napus) by providing a bridge to disease along roadsides and paddocks throughout grain-growing areas.