The presence of Phytophthora infestans in the rhizosphere of a wild Solanum species may contribute to off-season survival and pathogenicity

We evaluated oomycete presence and abundance in the rhizosphere of wild perennial Solanum species to investigate the presence of plant pathogenic or mycoparasitic species. Furthermore, we investigated whether these plant species could function as hosts, or associated plants, for off-season survival of economically important pathogens. We collected soil samples in Sweden from Solanum dulcamara and as a control from Vitis vinifera over all four seasons of a year, and in New Zealand from Solanum nigrum and Solanum laciniatum in the summer. Species identification, confirmed by ITS and Cox2 sequencing, and root infection assays on the crop plant Solanum tuberosum and on S. dulcamara, suggested the presence of mainly Pythiales species. In Sweden, we also found evidence for the presence of Phytophthora infestans, the causal agent of potato late blight, in the rhizosphere of S. dulcamara. These Ph. infestans isolates had no negative effects on root growth of S. dulcamara in Sweden, but were more pathogenic on potato leaves than a common lab strain. Oomycete diversity measures indicated a high similarity between seasons and countries. In conclusion, our study suggests a previously unknown overwintering strategy for the pathogen Ph. infestans, indicating a possible influence of the wild species S. dulcamara on the epidemiology of potato late blight in Sweden. •Evidence for previously unknown overwintering strategy for the pathogen, Phytophthora infestans.•Plant pathogenic Pythiales species are the most abundant oomycetes in the rhizosphere of wild solanum plants in both Sweden and New Zealand.•Oomycete diversity measures indicated a high similarity between seasons and countries.