Newly recognized bacteria involved in trunk scab and canker of white and hybrid poplars

In a 4-year-old collection of native Italian Populus alba, growing in the eastern Po valley, many trunks showed severe symptoms characterized by brown spots, similar to trunk scab and/or by cankers. Canker-like growths, often with gall-like-formations in the earlier developmental phases were also found on some clones of P. trichocarpa and their hybrids, as well as on P. deltoides growing in several Northern Italian nurseries. Bacteria and fungi present in the affected tissues and potentially involved in the disease were examined. No fungi were detected, however, several species of bacteria were isolated and identified: Pseudomonas mendocina and Erwinia herbicola group, from the brown spots; Erwinia carotovora sub sp. carotovora and, occasionally, E. herbicola group, from cankers. Only E. carotovora sub sp. carotovora produced clear symptoms of canker when artificially inoculated on young plants of different poplar species. This is the first time this symptomology on poplar species has been clearly related to E. carotovora sub sp. carotovora.