Bacteria associated with vascular wilt of poplar

Abstract In 2017, the 560-ha area of hybrid poplar plantation in northern Poland showed symptoms of tree decline. Leaves appeared smaller, turned yellow-brown, and were shed prematurely. Twigs and smaller branches died. Bark was sunken and discolored, often loosened and split. Trunks decayed from the base. Phloem and xylem showed brown necrosis. Ten per cent of trees died in 1–2 months. None of these symptoms was typical for known poplar diseases. Bacteria in soil and the necrotic base of poplar trunk were analysed with Illumina sequencing. Soil and wood were colonized by at least 615 and 249 taxa. The majority of bacteria were common to soil and wood. The most common taxa in soil were: Acidobacteria (14.757%), Actinobacteria (14.583%), Proteobacteria (36.872) with Betaproteobacteria (6.516%), Burkholderiales (6.102%), Comamonadaceae (2.786%), and Verrucomicrobia (5.307%).The most common taxa in wood were: Bacteroidetes (22.722%) including Chryseobacterium (5.074%), Flavobacteriales (10.873%), Sphingobacteriales (9.396%) with Pedobacter cryoconitis (7.306%), Proteobacteria (73.785%) with Enterobacteriales (33.247%) including Serratia (15.303%) and Sodalis (6.524%), Pseudomonadales (9.829%) including Pseudomonas (9.017%), Rhizobiales (6.826%), Sphingomonadales (5.646%), and Xanthomonadales (11.194%). Possible pathogens were Pseudomonas, Rhizobium and Xanthomonas. The initially endophytic character of bacteria is emphasized. Soil and possibly planting material might be the sources of pathogen inoculum.