Host range of Peronospora somniferi and Pe. meconopsidis within selected members of the Papaveraceae under controlled conditions

Opium poppy, belonging to the family Papaveraceae, is grown for its alkaloid compounds of pharmaceutical value. Downy mildew caused by Peronospora somniferi and Pe. meconopsidis, substantially impacts crop production. The present study was conducted to identify the host range of Pe. somniferi and Pe. meconopsidis within selected weed and ornamental members of the Papaveraceae family. Nine Papaver spp., Meconopsis cambrica and a nonhost control (tomato, Solanum lycopersicum) were challenged with both pathogens under controlled glasshouse or laboratory conditions using infested soil or foliar applied sporangia as inocula. Peronospora somniferi and Pe. meconopsidis induced disease symptoms, including sporulation, in at least one trial for all tested species except for Pa. atlanticum and tomato. Species-specific PCR testing of foliage of challenged plants confirmed infections by both pathogen species of symptomatic plants, identifying these as hosts. Positive PCR tests were also obtained from Pa. atlanticum plants for both pathogens. However, in the absence of pathogen sporulation structures as further evidence of infection, the host status of Pa. atlanticum remains inconclusive. Testing of seeds collected from Pe. somniferi and Pe. meconopsidis infected plants of Pa. somniferum, Pa. dubium, Pa. rhoeas and Pa. nudicaule showed presence of both pathogens, indicating likely ability for seed transmission in these species. We identified new hosts of these pathogens and discuss potential implications of these alternative hosts in pathogen survival, dissemination and epidemic initiation.