Peptidoglycan hydrolases are enzymes that cleave the peptidoglycan of the bacterial cell wall, facilitating cell growth, cell division, and peptidoglycan turnover. Xanthomonas citri subsp. citri (X. citri), the causal agent of citrus canker, encodes an Escherichia coli M23 peptidase EnvC homolog. EnvC is a LytM factor required for septal peptidoglycan splitting and daughter cell separation. In this study we investigate how EnvC contributes to the virulence and cell separation of X. citri. We observed that disruption of the X. citri envC gene (ΔenvC) led to a reduction in virulence. Upon inoculation into leaves of Rangpur lime (Citrus limonia Osbeck), the X. citri ΔenvC mutant showed a delay in causing citrus canker symptoms compared with the wild-type X. citri strain. Mutant complementation restored the X. citri wild type phenotype. Subcellular localization confirmed that X. citri EnvC is a periplasmic protein. Moreover, the X. citri ΔenvC mutant exhibited elongated cells, indicative of a cell division defect. These findings support the role of EnvC in regulating virulence, cell wall organization, and cell division in X. citri.

The Fusarium fujikuroi species complex (FFSC) includes socioeconomically important pathogens that cause disease and/or mycotoxin contamination on numerous crops. Here, we used comparative genomics to elucidate processes underlying the ability of pine-associated and grass-associated FFSC species to colonize tissues of their respective plant hosts. We characterized the identity, possible functions, evolutionary origins, and chromosomal positions of the host-range-associated genes encoded by the two groups of fungi. The 72 and 47 genes identified as unique to the respective genome groups were potentially involved in diverse processes, ranging from transcription, regulation, and substrate transport, through to virulence/pathogenicity. Most emerged early during the evolution of Fusarium/FFSC and were subsequently retained only in some lineages, while some had origins outside Fusarium. Although differences in the densities of these genes were especially noticeable on the conditionally dispensable chromosome of F. temperatum (representing the grass-associates) and F. circinatum (representing the pine-associates), the host-range-associated genes tended to be located towards the subtelomeric regions of chromosomes. Taken together, these results demonstrate that multiple mechanisms drive the emergence of genes in grass- and pine-associated FFSC taxa examined and highlighted the diversity of molecular processes potentially underlying niche-specificity in these and other Fusarium species.

Lasiodiplodia theobromae, as one of the causing agents associated with Chinese hickory trunk cankers, has caused huge economic losses to the Chinese hickory industry due to its extremely strong pathogenicity. Though the biological characteristics of this pathogen and the occurrence pattern of this disease have been reported, few studies have focused on investigating the mechanisms responsible for L. theobromae survival strategies and pathogenicity. The high-quality genome data and the efficient transformation system are the basis for researching above mechanism events. In this study we sequenced and assembled L. theobromae strain LTTK16-3, and established the first protoplasmic preparation method and polyethylene glycol (PEG) -mediated genetic transformation system for L. theobromae. These genetic information and transformation methods established the foundation for the future mechanisms study of L. theobromae and set up the possibility of targeted molecular improvements for Chinese hickory canker control.

Field observations of external wounds associated with two common tree injection methods compared open (plug-less) and sealed (plug) systems in green ash (Fraxinus pennsylvanica Marshall) trees . A wound from any cause within 1.37 meters above the ground was common with 28.8% of all trees. The open system had statistically fewer (p<0.001) trees with at least one wound (11.6% of trees) than the sealed system (47.4% of trees). The open system had fewer (P<0.001) wounds (0.17, 0.04 SE) per tree and a smaller (P<0.001) total wound area (25.5 cm2, 8.7 SE) per tree, compared to the sealed system wounds (1.14, 0.13 SE) per tree and the total wound area (99.7 cm2, 16.2 SE) per tree. The incidence of a tree with a wound(s) within 1.37 m above the ground was 7.2 times more likely with trees treated though the sealed system. Wounds in the sealed system were observed to appear to have a high rate of improper application of plugs, which was associated in 77% of the cases to explain the wounds. Implications of study results are further provided to best protect ash trees, while at the same time reducing the incidence external wounding on ash trees.

The airborne inoculum of Fusarium circinatum, the fungal pathogen causing Pine Pitch Canker (PPC), is one of the main means of spread of the disease in forest stands and forest nurseries. Since this world-wide known pathogen was introduced in Europe, its biology in this newly infected area still remains scarcely known. To shed more light on this topic, we set an experiment on a naturally PPC infected forest of Monterey pine in Galicia (NW Spain) with the following two goals: (i) to describe the seasonal spore dispersal pattern during one year of regular sampling and (ii) to assess the spatial spore dispersal pattern around the infested plot. Portable rotating arm spore traps were used and complemented with meteorological measurements. The abundance of F. circinatum spores in the samples was evaluated by quantitative PCR (qPCR) with hydrolysis probe. The results showed almost permanent occurrence of the air inoculum throughout the whole year, being detected in 27 of the 30 samplings. No clear temporal trends were observed, but higher air inoculum was favoured by previous lower air temperatures and lower leaf wetness. Conversely, neither rainfall nor air humidity seemed to have any significant importance. The spatial spread of the inoculum was noted to be successful up to a distance of 1000 m in the wind direction, even with winds of just 5 m s^-1. Our study shows that rotating arm spore traps combined with qPCR may be an efficient tool for F. circinatum detection.

The increase in arrivals of new forest pests highlights the need for effective phytosanitary legislation and measures. This paper introduces legislation targeted at prevention and management of potential introductions of forest pests and pathogens. A summary is given on plant health regulations on a global and regional level with detailed information on the situation in the European Union (EU). The current and new European legislation is discussed and a particular focus is given on eradication and contingency plans for Fusarium circinatum.