Sint-Katelijne-Waver, Belgium
Sint-Katelijne-Waver, Belgium

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Rombouts S.,Catholic University of Leuven | Rombouts S.,Belgium Institute for Agricultural and Fisheries Research | Van Vaerenbergh J.,Belgium Institute for Agricultural and Fisheries Research | Volckaert A.,Vegetable Research Center | And 6 more authors.
European Journal of Plant Pathology | Year: 2016

Pseudomonas syringae pv. porri causes bacterial leaf spot and blight of leek (Allium porrum) and is in wet crop seasons responsible for substantial losses. The local diversity within this pathogen in Flanders, Belgium, was investigated to obtain insights into its epidemiology. Therefore, symptomatic leek leaves were collected from 112 fields and bacteria were isolated. An oxidase negative, HR positive, fluorescent Pseudomonas was consistently recovered from the diseased tissues. Isolates were identified as P. syringae pv. porri by rpoD gene sequencing and by confirmation of pathogenicity in leek. Genomic profiles generated with BOX-PCR subdivided them into two groups, with one group containing 5 of the 37 analyzed strains. Those five isolates were all obtained in 2012 and the plant origins indicated seed transmitted infection. Draft genome sequences were produced for a P. syringae pv. porri strain from each BOX group and sequences of seven housekeeping genes were extracted for multi locus sequence analysis (MLSA). This resulted in the clustering of both P. syringae pv. porri strains with the P. syringae pv. oryzae strain 1_6 as did the whole genome sequence comparisons by ANI analysis. The P. syringae pv. porri isolates, designated LMG 28495 and LMG 28496, differed in a type III effector gene, HrpW, and in the number of mobile elements in the genome. Overall, the data demonstrate that two P. syringae pv. porri variants are present in symptomatic leek in Flanders which can be discriminated and possibly traced using a genomic profiling method such as BOX-PCR. Furthermore, the draft genome sequences of both strains will facilitate the development of sensitive and specific methods for early detection. © 2015, Koninklijke Nederlandse Planteziektenkundige Vereniging.


De Swaef T.,Ghent University | Vermeulen K.,Inagro | Vergote N.,Research Center for Vegetable Production | Van Lommel J.,Research Station for Vegetable Production PSKW | And 3 more authors.
Acta Horticulturae | Year: 2015

Although growers seem to be able to control the incidence of tipburn in soilgrown lettuce (Lactuca spp.), this physiological disorder causes substantial yield losses in hydroponics (up to 50%). Tipburn is generally considered to be a calcium deficiency related disorder, but literature exhibits apparently contradictory findings, because the research always focused on the effects of the environment on the occurrence of tipburn, whereas the plant physiological aspects were seldom included. Therefore, there is a strong need for a plant physiological interpretation of the tipburn disorder, which correlates the different environmental effects to the plant physiological processes. In this study, we present the use of plant sensors to assess the plant physiological response to its environment with respect to the incidence of tipburn. As such, stem diameter and leaf thickness were continuously monitored, because variations in these variables are strongly related to variations in the plant water relations, turgor pressure and growth rate. Leaf thickness measurements were combined with a mechanistic model to detect periods of water deficits or abrupt changes in turgor pressure. This approach could additionally help to monitor root pressure and investigate the hypothesis that root pressure has beneficial effects on the supply of calcium to slowly transpiring leaves. As such, growth rate, supply of calcium to low transpiring leaves and abrupt variations in turgor pressure, all of which are associated with tipburn, could be instantly visualised by these plant sensors and consequently identify environmental drivers for tipburn.


Declercq B.,Ghent University | Declercq B.,Provincial Research and Advisory Center for Agriculture and Horticulture | Devlamynck J.,Ghent University | de Vleesschauwer D.,Ghent University | And 4 more authors.
Journal of Phytopathology | Year: 2012

White tip, caused by Phytophthora porri, is a devastating disease in the autumn and winter production of leek (Allium porrum) in Europe. This study investigated the disease cycle of P. porri in laboratory and field conditions. Oospores readily germinated in the presence of non-sterile soil extract at any temperature between 4 and 22°C, with the formation of sporangia which released zoospores. The zoospores survived at least 7weeks in water at a temperature range of 0 till 24°C. Microscopic examinations revealed that zoospores encysted and germinated on the leek leaf surface and hyphae entered the leaf directly through stomata or by penetrating via appressoria. Oospores were formed in the leaves within 6days, while sporangia were not produced. By monitoring disease progress in fields with a different cropping history of leek, it could be deduced that P. porri survives in soil for up to 4years. Disease progress during three consecutive years was correlated with average daily rainfall in the infection period. Disease incidence on leek was reduced when rain splash was excluded by growing the plants in an open hoop greenhouse. Based on these findings, we propose a disease cycle for P. porri in which oospores germinate in puddles, and zoospores reach the leaves by rain splash and survive in water in the leaf axils, from where they infect the plant by direct penetration or via stomata. When conditions become unfavourable, oospores are produced in the leaves which again reach the soil when leaves decay. Secondary spread of the disease by sporangia does not seem to be important. © 2011 Blackwell Verlag GmbH.


Declercq B.,Ghent University | Van Buyten E.,Ghent University | Claeys S.,Ghent University | Cap N.,Vegetable Research Center | And 3 more authors.
European Journal of Plant Pathology | Year: 2010

White tip, caused by Phytophthora porri, is a destructive disease in the cultivation of European leek (Allium porrum). P. porri and closely related species such as P. brassicae, P. primulae and P. syringae belong to the phylogenetic clade 8b within the genus Phytophthora. The objectives of this study were to establish the position of P. porri and closely related species within the Phytophthora clade 8b; to study genetic variation among P. porri isolates from leek and closely related species and to test the hypothesis that host-driven speciation has occurred within this clade. AFLP analysis could clearly make a distinction between isolates of P. porri from Allium species and related Phytophthora species such as P. brassicae, P. syringae and P. primulae. DNA similarity and cluster analysis based on 353 markers demonstrated little genetic diversity within the P. porri population from Allium species although Belgian and Dutch P. porri isolates from leek could be distinguished from Japanese P. porri isolates from other Allium species and the P. porri isolate from carrot. Our results point to incipient speciation within the P. porri isolates, which could have been driven by the host plant or by geographic isolation. ITS sequence analysis confirmed the results obtained by AFLP and showed a close relationship between P. porri isolates from Allium and P. primulae and between the P. porri isolate from carrot and P. brassicae. We hypothesize that interspecific hybridization has occurred within this clade. © 2010 KNPV.

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