|Plantweerbaarheid in snij Hortensia
Noort, F.R. van; Jacobs, G. ; Dijkstra, T. ; Marwijk, D. van - \ 2013
Wageningen : DLV Plant/LTO Groeiservice/Flora Holland/Wur Glastuinbouw - 44 p.
Relatie tussen microklimaat en vaasleven bij roos
Weel, P.A. van; Eveleens, B.A. ; Keim, E. ; Jacobs, G. - \ 2013
Bleiswijk : Wageningen UR Glastuinbouw (Rapporten WUR GTB 1253) - 40
rozen - rosaceae - microklimaat - vaasleven - meting - bloementeelt - teelt onder bescherming - nederland - roses - rosaceae - microclimate - vase life - measurement - floriculture - protected cultivation - netherlands
Bij snijrozen is getracht een beeld te krijgen van het microklimaat in het gewas met sensoren die de temperatuur van knop en blad meten, aangevuld met metingen van RV en temperatuur van de omringende lucht. Gelijktijdig is bij 2 cultivars, ‘Passion’ en ‘Avalanche Peach’, en op twee plekken in de kas het vaasleven bepaald. Op die manier werd gehoopt een indicatie te vinden voor de invloed van het microklimaat op het optreden van met name botrytis. De meting bleek niet in staat om een direct verband aan te tonen tussen microklimaat en botrytis. Wel werd duidelijk dat de meest waarschijnlijke oorzaak gezocht moet worden in perioden dat niet belicht wordt in koude luchtstromen in de kas als gevolg van kieren in het scherm en van uitstraling van de knoppen naar een koude hemel. Meten van de temperaturen van knop en blad bleek door de kwetsbaarheid van het thermokoppel moeilijk uitvoerbaar, maar kan eenvoudig vervangen worden door een thermische camera. Aanvullend zal er echter een meetmethode ontwikkeld moeten worden om de RV in de grenslaag rondom knop of blad betrouwbaar te kunnen meten voordat een meting van het microklimaat praktische waarde kan hebben bij het voorspellen van de kans op natslag.
Symbiotic bacteria (Erwinia sp.) in the gut of Frankliniella occidentalis (Thysanoptera: Thripidae) do not affect its ability to transmit tospovirus
Vries, E.J. de; Wetering, F. van de; Hoek, M.M. van der; Jacobs, G. ; Breeuwer, J.A.J. - \ 2012
European Journal of Entomology 109 (2012)2. - ISSN 1210-5759 - p. 261 - 266.
western flower thrips - spotted wilt virus - insect vector - protein - tabaci
Tomato spotted wilt virus (TSWV) is one of the most harmful plant viruses and one of its most important vectors is the western flower thrips [Frankliniella occidentalis Pergande (Thysanoptera: Thripidae)]. Recently, we reported the close association of Erwinia sp. gut bacteria with this species of thrips. The first instar larvae acquire these bacteria from their food source. A high proportion of adult western flower thrips transmit TSWV after acquiring the virus during the first larval stage when there are no bacteria in their gut. A considerably lower proportion of adults that acquire the virus early in the second instar transmit virus and none of those exposed to virus late on in the second instar do so. The highest prevalence and total number of symbiotic bacteria are recorded in the guts of second instar thrips. This leads to the hypothesis that the build up of bacteria in the gut reduces the acquisition of TSWV, resulting in a lower capacity to transmit the virus. To test this hypothesis, the transmission of this virus by symbiotic and aposymbiotic adult thrips of the NL3 population was studied. Comparison of virus transmission by adult thrips, the larvae of which either had or lacked gut bacteria and were exposed to virus in either the first or second instar, revealed no difference in the ability of symbiotic and aposymbiotic adults to transmit this virus. We conclude that virus transmission is not affected by the number of the symbiotic bacteria Erwinia sp. present in the gut of thrips larvae
Lack of evidence for western flower thrips biotypes base don intra and inter-strain variation in gut bacteria
Vries, E.J. de; Jacobs, G. ; Kogel, W.J. de; Hoek, M. van der; Breeuwer, J.A.J. - \ 2010
In: Symbiosis of thrips and gutbacteria, PhD thesis van E.J. de Vries Amsterdam : Universiteit van Amsterdam, Faculty of Science - ISBN 9789076894850 - p. 110 - 124.
Western flower thrips is a polyphagous insect, which during the last 30 years has become a world wide pest. It was found earlier that these thrips are associated with a type of Erwinia species gut bacteria. In this study we examine the variation of bacteria within and between thrips individuals and try to find evidence for biotypes in western flower thrips regarding the type of gut bacteria. The existence of biotypes in this thrips species has been suggested by different authors. For example, thrips populations have been found that differ in resistance against pesticides and in their ability to transmit plant viruses. With biotypes we mean groups of individuals (strains, populations, lines) of a species which differ in one or more traits with other groups of that species. The gut bacteria of thrips are acquired by young thrips larvae via the host plant and have a beneficial effect on thrips development and oviposition. We studied thrips strains from different countries and host plants, and the isofemale lines that were created from them, on bean plant leaves. All thrips lines that we studied contained Erwinia species gut bacteria. Morphological and biochemical characteristics of gut bacteria from the thrips isofemale lines were similar to the Erwinia type strain from the reference, a thrips strain cultured on chrysanthemum in Amsterdam (TAC 93.XII.8). Per isofemale line we studied five thrips individuals and per thrips we studied four bacterial colonies, with RAPD markers. The genetic variation between bacteria isolated from thrips was as large among isofemale lines as within isofemale lines. No evidence for thrips biotypes was found. Bacteria within one thrips individual show a stronger degree of similarity than bacteria from different thrips individuals within a single rearing. This is probably due to a bottleneck caused by the limited number of successful infections of bacteria into the gut of the thrips
Onion thrips, Thrips tabaci, have gut bacteria that are closely related to the symbionts of the western flower thrips, Frankliniella occidentalis
Vries, E.J. de; Wurff, A.W.G. van der; Jacobs, G. ; Breeuwer, J.A.J. - \ 2008
Journal of Insect Science 8 (2008). - ISSN 1536-2442 - p. 1 - 11.
microbial ecology - thysanoptera - transmission - insects - growth - evolutionary - association - resistance - wolbachia - termites
It has been shown that many insects have Enterobacteriaceae bacteria in their gut system. The western flower thrips, Frankliniella occidentalis Pergande [Thysanoptera: Thripidae], has a symbiotic relation with Erwinia species gut bacteria. To determine if other Thripidae species have similar bacterial symbionts, the onion thrips, Thrips tabaci, was studied because, like F. occidentalis, it is phytophagous. Contrary to F. occidentalis, T. tabaci is endemic in Europe and biotypes have been described. Bacteria were isolated from the majority of populations and biotypes of T. tabaci examined. Bacteria were present in high numbers in most individuals of the populations studied. Like F. occidentalis, T. tabaci contained one type of bacterium that clearly outnumbered all other types present in the gut. This bacterium was identified as an Erwinia species, as was also the case for F. occidentalis. However, its biochemical characteristics and 16S rDNA sequence differed from the bacteria present in F. occidentalis.
The CALUX bioassay: current status of its application to screening food and feed
Hoogenboom, L.A.P. ; Goeyens, L. ; Carbonnelle, S. ; Loco, J. van; Beernaert, H. ; Baeyens, W. ; Traag, W.A. ; Bovee, T.F.H. ; Jacobs, G. ; Schoeters, G. - \ 2006
TrAC : Trends in Analytical Chemistry 25 (2006)4. - ISSN 0165-9936 - p. 410 - 420.
gene-expression calux - dioxin-like compounds - ah receptor - international validation - blood-plasma - pcbs - samples - milk - contamination - activation
The CALUX bioassay is at present the best screening method for dioxins and dioxin-like (dl) polychlorinated biphenyls (PCBs) in food and feed, and the only assay used in routine monitoring and during larger incidents. Furthermore, the use of bioassays in addition to chemical reference methods allows the discovery of novel contaminants with potentially adverse effects on human health. The CALUX bioassay shows a clear dose-related response both with dioxin standards and contaminated samples, but requires a clear strategy with respect to decision limits, necessary to deal with the many different action and tolerance limits in European Union (EU) legislation. In future, the CALUX bioassay will profit from further optimization, especially with respect to the clean-up procedure. As demonstrated in the limited number of interlaboratory studies performed so far, this should lead to an even more robust assay that can be easily introduced into less experienced laboratories. The present article discusses the different issues, based on some practical examples from the EU-DIFFERENCE project and gives recommendations for future studies.