Plants harboring the potato blackleg bacteria

Abstract Potato blackleg is an intractable disease over the world and incited by five bacterial species, i.e., Pectobacterium brasiliense (Pb), P. parmentieri , P. atrosepticum , Dickeya dianthicola (Ddi), and D. chrysanthemi in Japan. A total of collected 1,018 plants belonging to 19 species from eight families were collected inside and outside potato fields, as well as their rhizosphere, to confirm if they harbored the bacterial pathogens by BIO-PCR (a combined biological and enzymatic amplification). Daucus carota subsp. carota , Avena strigosa and Rumex obtusifolius were found to carry Pb in the underground parts (root or rhizome) and rhizosphere. Similarly, Artemisia montana , Petasites japonicus subsp. giganteus , Taraxacum officinale , and Solidago gigantea var. leiophylla held Ddi in their rhizome and/or rhizosphere. Pb and Ddi were found on these plant species even 3–5 years after potato production. In inoculation test, D. carota subsp. carota , A. strigosa , and R. obtusifolius got infected with Pb by injecting bacterial suspension into healthy plants. P. japonicus subsp. giganteus and S. gigantea var. leiophylla were also infected with Ddi in the test. Pb isolates from A. strigosa or R. obtusifolius caused blackleg on potato when each of these was inoculated on seed tubers before planting. This is the first implication that A. strigosa , R. obtusifolius , and D. carota subsp. carota are a host plants of Pb, and Pb and Ddi can live long on host in field environment.