No abstract

No abstract

Xanthomonas theicola is the causal agent of bacterial canker on tea plants. There is no complete genome sequence available for X. theicola, a close relative of the species X. translucens and X. hyacinthi, thus limiting basic research for this group of pathogens. Here we release a high-quality complete genome sequence for the X. theicola type strain, CFBP 4691T. Single-molecule real-time sequencing with a mean coverage of 264X revealed two contigs of 4,744,641 bp (chromosome) and 40,955 bp (plasmid) in size. Genome mining revealed the presence of non-ribosomal peptide synthases, two CRISPR systems, the Xps type 2 secretion system, and the Hrp type 3 secretion system. Surprisingly, this strain encodes an additional type 2 secretion system and a novel type 3 secretion system with enigmatic function, hitherto undescribed for xanthomonads. Four type 3 effector genes were found on complete or partial transposons, suggesting a role of transposons in effector gene evolution and spread. This genome sequence fills an important gap to better understand the biology and evolution of the early-branching xanthomonads, also known as clade-1 xanthomonads.

Following its introduction from Asia in the 1990s, the ascomycete Hymenoscyphus fraxineus has caused a severe dieback of Fraxinus excelsior in Europe. In this study, the virulence of 200 H. fraxineus isolates were assessed and compared. These isolates equally represented (i) two geographically distant populations with a different disease history (Switzerland, recently established populations at the epidemic front versus Lithuania, old established populations), and (ii) isolates from two different types of host tissue (necrotic bark lesions as dead‐end tissue versus fallen leaf petioles as primary host tissue). Inoculations conducted on 3‐year‐old F. excelsior seedlings showed that the vast majority of the isolates (98%) were able to induce necrotic bark lesions after 10 months. Although a high variation in virulence was observed among isolates, no significant differences were detected between the older and the epidemic‐front populations. Decline in virulence of populations of invasive organisms is generally assumed with increasing age of epidemics. However, this does not appear to hold true for H. fraxineus. Either the Lithuanian population is still too young (15 to 20 years old) to show a decline in virulence, or the size of the host population may still not be critical for pathogen survival. Given that bark lesions represent an epidemiological dead end and do not benefit the survival of H. fraxineus, a trend towards reduced ‘bark virulence’ of isolates originating from leaf petioles compared to isolates from the bark lesions was expected. However, such a trend was observed neither in old, nor in recently established populations.

The aim of this study was to assess belowground occurrence, persistence and possible impact of the biocontrol agent Phlebiopsis gigantea (Fr.) Jülich on soil fungi. Sampling of soil and roots of Picea abies (L.) H. Karst. was carried out at 12 P. gigantea-treated and five nontreated control sites representing 1- to 60-month-old clear-cuts and thinned forest sites in Finland and Latvia. The 454-sequencing of ITS rRNA from fine roots, humus and mineral soil resulted in 8626 high-quality fungal sequences. Phlebiopsis gigantea represented 1.3% of all fungal sequences and was found in 14 treated and nontreated sites and in all three substrates. In different substrates, the relative abundance of P. gigantea at stump treatment sites either did not differ significantly or was significantly lower than in nontreated controls. No significant correlation was found between the time elapsed since the tree harvesting and/or application of the biocontrol and abundance of P. gigantea in different substrates. In conclusion, the results demonstrate that P. gigantea occasionally occurs belowground in forest ecosystems but that stump treatment with the biocontrol agent has little or no impact on occurrence and persistence of P. gigantea belowground, and consequently no significant impact on soil fungi.