Abstract
In 2017, a 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 in the necrotic base of poplar trunk were analyzed 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 (14.76%), Actinobacteria (14.58%), Proteobacteria (36.87) with Betaproteobacteria (6.52%), (6.10%), Comamonadaceae (2.79%), and Verrucomicrobia (5.31%).The most common taxa in wood were: Bacteroidetes (22.72%) including Chryseobacterium (5.07%), Flavobacteriales (10.87%), Sphingobacteriales (9.40%) with Pedobacter cryoconitis (7.31%), Proteobacteria (73.79%) with Enterobacteriales (33.25%) including Serratia (15.30%) and Sodalis (6.52%), Pseudomonadales (9.83%) including Pseudomonas (9.02%), Rhizobiales (6.83%), Sphingomonadales (5.65%), and Xanthomonadales (11.19%). Possible pathogens were Pseudomonas, Rhizobium and Xanthomonas. The potential initial, endophytic character of bacteria is discussed. Soil and possibly planting material might be the reservoir of pathogen inoculum.
Highlights
Poplars are distributed predominantly throughout the northern hemisphere
The majority of bacteria were common to soil and wood
Sequencing of the 16S rRNA gene is highly useful for bacterial classification because of its presence in almost all bacteria, its ability to exist as a multigene family or operon, its resistance to change over time, and its size (1500 bp long)
Summary
Poplars are distributed predominantly throughout the northern hemisphere. Because of their rapid growth, wild Populus spp. and their hybrids are currently planted over huge areas worldwide as ornamental plants for landscape greening, production of wood, and multiple industrial uses (Jansson and Douglas 2007).Poplar’s susceptibility to phytopathogens is the main obstacle to its exploitation (reviewed in Newcombe 1996). Poplars are distributed predominantly throughout the northern hemisphere. Because of their rapid growth, wild Populus spp. and their hybrids are currently planted over huge areas worldwide as ornamental plants for landscape greening, production of wood, and multiple industrial uses (Jansson and Douglas 2007). Pseudomonas aeruginosa (Schröter) Migula appeared on poplar recently (Attila et al 2008). It causes soft rot, which results in wilting, with death of trees occurring quickly, even in less than 48 h. In the 1990s, the bacterial genus Brenneria was reported to cause canker of trees including poplar (Biosca et al 2006). Large portions of the plantation areas of the hybrid poplar Populus × euramericana in China and Hungary are affected by potentially lethal Lonsdalea populi (formerly Lonsdalea quercina subsp. populi)
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