EPPO Contingency Exercise Workshop for a Forestry Pest,Zlatibor, Serbia, 2018‐11‐27/29

An EPPO Contingency Planning Workshop for a Forestry Pest was held in Zlatibor, Serbia, between 27 and 29 November 2018. In total, 55 experts from 21 EPPO member countries attended the 3‐day workshop. Participants were split into four groups for the exercise and each group acted as an ‘outbreak management team’ for a scenario based on the finding of a quarantine pest for forestry. Only when the exercise had started were participants informed that the outbreak scenario centred around the fictitious discovery of pinewood nematode (Bursaphelenchus xylophilus) in the Tara National Park in Serbia. As the scenario developed, each team had to organize themselves to manage a number of issues designed to mimic the development of an outbreak over the first month following its detection. It was clear from the feedback from participants that that contingency planning workshop was a valuable exercise for EPPO to conduct and participants highlighted the importance of it to prepare themselves for real‐life situations.     

Influence of temperature on infection and establishment of ‘Candidatus Liberibacter americanus’ and ‘Candidatus Liberibacter asiaticus’ in citrus plants

The objectives of this work were (i) to determine the influence of temperature on infection of citrus by ‘Candidatus Liberibacter asiaticus’ and ‘Candidatus Liberibacter americanus’, the two bacterial species associated with citrus huanglongbing (HLB) in Brazil, and (ii) to determine the influence of temperature on citrus colonization by ‘Ca. L. asiaticus’, which has taken over from ‘Ca. L. americanus’ as the predominant species in Brazil since 2008. Two experiments were carried out with graft‐inoculated Valencia oranges on Rangpur lime rootstocks. Immediately after inoculation the plants were maintained for 423 days in growth chambers under the following night/day temperature conditions: 17/22, 22/27 or 27/32°C, with a dark/light photoperiod of 8/16 h. Infection and colonization of plants were determined using quantitative PCR (qPCR). ‘Candidatus Liberibacter americanus’ did not infect the plants maintained at 27/32°C; however, infection by ‘Ca. L. asiaticus’ occurred at all studied temperatures. Two months after inoculation, ‘Ca. L. asiaticus’ was distributed throughout the inoculated plants, with mean C_t values in the range of 30–31 for leaves and 25–28 for roots. Over time, ‘Ca. L. asiaticus’ reached the highest titres in mature leaves (mean C_t value = 26·7) of citrus plants maintained at 22/27°C. ‘Candidatus Liberibacter asiaticus’ colonization of citrus plants was negatively affected by the daily temperature regime of 27/32°C (mean C_t value in mature leaves = 33·6).     

‘Pharmacokinetic’ and ‘pharmacodynamic’ design of lipophilic drugs based on a structural model for drug interactions with biological membranes

The pharmacokinetic profile a drug exhibits will ultimately depend on how the drug molecule interacts with the different cell membranes it encounters en route to its target site of action. Even if the drug molecule targets a soluble protein as its final site of action, there is a reasonable probability that it will interact with some cell membrane on its pathway to this biological target. In some cases, the final protein, lipid or sugar moiety target could be an integral part of the cell membrane architecture whereby the drug's interaction with the cell membrane could influence its pharmacodynamic profile as well, especially if the final site of action is an integral membrane-bound receptor protein. In either case, drug transport across a cell membrane or within the cell membrane lipid bilayer compartment can dictate partial or dominant control of the drug's bioavailability. A molecular understanding of the equilibrium membrane partition coefficient, the rates of drug partitioning into and out of a cell membrane and the equilibrium location of the drug within the cell membrane can provide critical chemical design strategies for altering overall drug bioavailability and optimal pharmacokinetics.     

Theory,preparation and ‘exhaustion’ on wool fibres of pesticide emulsions. III.—‘exhaustion’ of pesticide emulsions on wool fibres

The spreading on the wool surface of emulsion droplets, stabilised by blends of calcium dodecylbenzene-sulphonate and polyoxyethylene nonylphenol condensates, and containing toxaphene and diazinon as toxicants, kerosene and xylene as solvents, is mainly due to the intermolecular forces operating at the resulting interface, i.e. van der Waals forces, π- and H-bonds.     

Virulence of ‘Dickeya solani’ and Dickeya dianthicola biovar‐1 and ‐7 strains on potato (Solanum tuberosum)

Studies were conducted to explain the relative success of ‘Dickeya solani’, a genetic clade of Dickeya biovar 3 and a blackleg‐causing organism that, after recent introduction, has spread rapidly in seed potato production in Europe to the extent that it is now more frequently detected than D. dianthicola. In vitro experiments showed that both species were motile, had comparable siderophore production and pectinolytic activity, and that there was no antagonism between them when growing. Both ‘D. solani’ and biovar 1 and biovar 7 of D. dianthicola rotted tuber tissue when inoculated at a low density of 10³ CFU mL^?1. In an agar overlay assay, D. dianthicola was susceptible to 80% of saprophytic bacteria isolated from tuber extracts, whereas ‘D. solani’ was susceptible to only 31%, suggesting that ‘D. solani’ could be a stronger competitor in the potato ecosystem. In greenhouse experiments at high temperatures (28°C), roots were more rapidly colonized by ‘D. solani’ than by biovar 1 or 7 of D. dianthicola and at 30 days after inoculation higher densities of ‘D. solani’ were found in stolons and progeny tubers. In co‐inoculated plants, fluorescent protein (GFP or DsRed)‐tagged ‘D. solani’ outcompeted D. dianthicola in plants grown from vacuum‐infiltrated tubers. In 3 years of field studies in the Netherlands with D. dianthicola and ‘D. solani’, disease incidence varied greatly annually and with strain. In summary, ‘D. solani’ possesses features which allow more efficient plant colonization than D. dianthicola at high temperatures. In temperate climates, however, tuber infections with ‘D. solani’ will not necessarily result in a higher disease incidence than infections with D. dianthicola, but latent seed infection could be more prevalent.     

Transmission of ‘Candidatus Liberibacter solanacearum’ in carrot seeds

A protocol for the specific detection and quantification of ‘Candidatus Liberibacter solanacearum’ in carrot seeds using real‐time PCR was developed. The bacterium was detected in 23 out of 54 carrot seed lots from 2010 to 2014, including seeds collected from diseased mother plants. The average total number of ‘Ca. L. solanacearum’ cells in individual seeds ranged from 4·8 ± 3·3 to 210 ± 6·7 cells per seed from three seed lots, but using propidium monoazide to target live cells, 95% of the cells in one seed lot were found to be dead. Liberibacter‐like cells were observed in the phloem sieve tubes of the seed coat and in the phloem of carrot leaf midrib from seedlings. The bacterium was detected as early as 30 days post‐germination, but more consistently after 90 days, in seedlings grown from PCR positive seed lots in an insect‐proof P2 level containment greenhouse. Between 12% and 42% of the seedlings from positive seed lots tested positive for ‘Ca. L. solanacearum’. After 150 days, symptoms of proliferation were observed in 12% of seedlings of cv. Maestro. ‘Candidatus Liberibacter solanacearum’ haplotype E was identified in the seeds and seedlings of cv. Maestro. No phytoplasmas were detected in seedlings with symptoms using a real‐time assay for universal detection of phytoplasmas. The results show that to prevent the entry and establishment of the bacterium in new areas and its potential spread to other crops, control of ‘Ca. L. solanacearum’ in seed lots is required.