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. Source
Vergote N.,Vegetable Research Center |
Marien H.,KH Kempen
Acta Horticulturae | Year: 2011
Both conventional and organic protected horticulture have to face problems of high energy costs. Companies growing organic vegetables are smaller than conventional producers, where electricity and heat cogeneration is a possible solution because of the larger, more suitable scale for introducing cogeneration. In addition to economic reasons, organic growers should implement extra efforts to reduce the use of non-renewable energy. Carbon dioxide is an important factor to enhance horticultural production and food quality. In a working group of growers and an energy specialist, all these parameters were put together. The best solution for small companies using carbon dioxide could be the use of a gas absorption heat pump (GAHP) in combination with Borehole Thermal Energy Storage (BTES) in an extra isolated greenhouse. As a result, this concept was installed at the organic research centre in Kruishoutem, Belgium. A new 1280 m 2 greenhouse divided into 6 compartments was installed. By using a double upper screen and polycarbonate in the outer walls, an U-value of 2.75 W m -2 K -1 was obtained. Three GAHP were installed with 41.6 kW thermal power delivered (delta T brine inlet - hot water outlet 35°C) in combination with both short-term and long-term cold and heat buffer storage (45 m 3 each, shortterm), BTES (28 holes of 100 m depth, long term) and an air handling unit to cool and dry the air (4750 m 3 h -1). During the summer, pump operation is dictated by the need for CO 2. The heat is collected short term in the heat buffer storage or long term in the BTES. The cold generated is used to dehumidify and cool the air so the ventilation requirement is reduced, and the emissions from the GAHP can be used for CO 2 fertilisation. During the winter, pump operation is dictated by the need for heat, in combination with the need for CO 2. This is achieved through preferred heat production at times of high radiation, when absorbed heat is shunted to short term storage. Cold that is produced can be used to dehumidify the air but is mainly used for exchange with the relatively high temperature (loaded in summer) in the BTES, so the temperature of the BTES (and soil) is back in balance at the end of the winter. The heat delivered from the BTES improves the efficiency of the GAHP. Source
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. Source
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. Source
Van Hoestenberghe S.,Catholic University of Leuven |
Fransman C.-A.,Catholic University of Leuven |
Luyten T.,Catholic University of Leuven |
Vermeulen D.,Catholic University of Leuven |
And 3 more authors.
Aquaculture Research | Year: 2016
A 10-week trial was conducted to determine the response of juvenile jade perch Scortum barcoo on the replacement of dietary fish oil (FO) in a fishmeal free diet. Three iso-nitrogenous, isocaloric and isolipidic diets were formulated, each containing a different primary fat source: FO, linseed oil (LO), and a mixture of Schizochytrium and LO. The substitution of FO with the mixture of Schizochytrium and LO did not cause a difference in growth. However, there was an 8% reduction in weight gain in fish fed dietary LO, indicating that juvenile jade perch do require a minimal concentration of dietary n-3 highly unsaturated fatty acids (HUFA). Fish fed the Schizochytrium diet stored more efficient n-3 HUFA and in particular DHA in their flesh, and retained a higher fillet recovery compared to fish fed FO. In addition, we demonstrated that jade perch are able to produce both n-3 HUFA and n-6 HUFA when dietary PUFA are present. Fish fed the LO diet for 10 weeks contained the lowest amount of n-3 HUFA in fillets among dietary treatment groups. However, feeding these fish the Schizochytrium diet for an additional 4 weeks increased the n-3 HUFA content towards the same concentration of n-3 HUFA found in the flesh of fish fed FO, without affecting the sensory properties of the fillets. In contrary, feeding the Schizochytrium diet for a continuous period of 14 weeks lowered overall sensory property scores. © 2016 John Wiley & Sons Ltd. Source