Efficacy of various physiochemical seed treatments for controlling poppy downy mildew in Papaver seed lots

Opium poppy (Papaver somniferum), is a commercially valuable crop, grown for the production of pharmaceutical alkaloids. The Australian poppy industry is the leading producer of legal opiates in the world. Downy mildew, caused by two oomycete species, Peronospora meconopsidis and Peronospora somniferi, is one of the most destructive diseases in commercial poppy growing regions, including Australia. To reduce downy mildew primary inoculum loads in commercial production, a series of physiochemical treatments of poppy seed were trialed. These included hypochlorite and electrolysis water solutions, heating via either steam or hot water, and microwave treatment of seed. Following treatment, seeds were tested for germination and emergence percentages. Downy mildew infestation rates of seed post-treatment were measured via quantitative PCR (qPCR) using species-specific primers. Treated seed was also sown into commercial potting mix to assess downy mildew transmission rates from seed to seedling with infection confirmed via qPCR. Optimal disease control was observed from treatment with electrolysis water (400 ppm for 5 min) which reduced P. somniferi infection incidence from 0.82 to 0.07% in 3 week old seedlings. Seed germination and emergence rates were also significantly improved by this treatment. Thus physiochemical treatments have the potential to reduce the seed transmission of downy mildew in poppy production seeds without detrimental effects on seed viability