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Bij de teelt van komkommer, tomaat en aubergine in uiteen lopende glastuinbouwgebieden in Nederland worden planten waargenomen in de teelt waarbij het wortelgestel een overmatige productie aan wortels laat zien. Het fenomeen dat daarom ook ‘overmatige wortelgroei’ wordt genoemd, uit zich door het ontstaan van veel extra wortels aan het grond- of steenwoloppervlak. De oorzaak van deze overmatige wortelgroei is de bacterie Agrobacterium rhizogenes. Deze bacterie wordt ook wel Agrobacterium radiobacter genoemd . In dit experiment zijn verschillende methoden of middelen onderzocht die de aanwezigheid en infectie van wortels met de Ri-plasmide afkomstig uit Agrobacterium rhizogenes in een kas kunnen voorkomen of verspreiding ervan kunnen inperken. De uitgevoerde proeven hebben als doel: Het ontwikkelen en testen van effectieve maatregelen die de aanwezigheid en verspreiding van overmatige wortelgroei in vruchtgroentegewassen kunnen beperken.

Mutations causing antibiotic resistance are often associated with a cost in the absence of antibiotics. Surprisingly, a new study found that bacteria adapting to increased temperature became resistant to rifampicin. By studying the consequences of the involved mutations in different conditions and genetic backgrounds, the authors illustrate how knowledge of two fundamental genetic properties, pleiotropy and epistasis, may help to predict the evolution of antibiotic resistance

Van 2009 tot 2011 werden kasproeven uitgevoerd om de kolonisatie van tomatenplanten met Clavibacter michiganensis subsp. michiganensis (Cmm) vanuit besmet zaad en de secundaire verspreiding van Cmm in een gewas te bestuderen.

For a quantitative understanding of the process of adaptation, we need to understand its “raw material,” that is, the frequency and fitness effects of beneficial mutations. At present, most empirical evidence suggests an exponential distribution of fitness effects of beneficial mutations, as predicted for Gumbel-domain distributions by extreme value theory. Here, we study the distribution of mutation effects on cefotaxime (Ctx) resistance and fitness of 48 unique beneficial mutations in the bacterial enzyme TEM-1 ß-lactamase, which were obtained by screening the products of random mutagenesis for increased Ctx resistance. Our contributions are threefold. First, based on the frequency of unique mutations among more than 300 sequenced isolates and correcting for mutation bias, we conservatively estimate that the total number of first-step mutations that increase Ctx resistance in this enzyme is 87 [95% CI 75–189], or 3.4% of all 2,583 possible base-pair substitutions. Of the 48 mutations, 10 are synonymous and the majority of the 38 non-synonymous mutations occur in the pocket surrounding the catalytic site. Second, we estimate the effects of the mutations on Ctx resistance by determining survival at various Ctx concentrations, and we derive their fitness effects by modeling reproduction and survival as a branching process. Third, we find that the distribution of both measures follows a Fréchet-type distribution characterized by a broad tail of a few exceptionally fit mutants. Such distributions have fundamental evolutionary implications, including an increased predictability of evolution, and may provide a partial explanation for recent observations of striking parallel evolution of antibiotic resistance

Phalaenopsis growers suffer from mayor losses up to 20% due to bacterial spot. This bacterial infection in caused by the Acidovorax avenae subsp. cattleyae. In practice this bacterial disease is also known as Pseudomonas. This bacterium is causing black leaf spots with a yellow border. Pseudomonas cattleyae is very contagious and is promoted by high temperatures en moist conditions. In this project Groen Agro Control laboratory (Delfgauw) has developed a molecular analysis method to detect Pseudomonas cattleyae in different matrices. The influence of the relative humidity on the development of Pseudomonas cattleyae is investigated during this research. The results show that a relative humidity of 90% strongly promotes infection of the bacteria. A relative humidity of 75% shows no extra dispersion of Pseudomonas cattleyae compared to a greenhouse compartment with a continuous relative humidity of 60%. This knowledge offers the opportunity to safe energy in the cultivation of Phalaenopsis. During this research the effects of water treatments on the dispersion of Pseudomonas cattleyae have been investigated. The results show that a treatment with hydrogen peroxide (20 ppm) offers the best reduction of dispersion. This treatment turns out to be better than the control and all other treatments. This research has led to new insights about the dispersal and optimal growing conditions of this bacteria, but leads to new questions. Questions, about other different dosages and the effects of other water treatments, but also about the optimal level to promote plant growth and reduce bacterial infections, have to be investigated in new research., Referaat Telers van Phalaenopsis hebben vooral in de opkweekfase last van infecties met de bacterie Acidovorax avenae subsp. cattleyae. In de praktijk spreekt men nog vaak over Pseudomonas. De bacterie veroorzaakt bladvlekken die bestaan uit zwarte ingezonken plek met een gele rand. In sommige gevallen kan de uitval oplopen tot wel 20%. De bacterieziekte is zeer besmettelijk en wordt door hoge temperaturen en veel vocht in de hand gewerkt. Groen Agro Control heeft in dit project een analysemethode ontwikkeld om de bacteriën met behulp van DNA technieken te detecteren. Tijdens het onderzoek is gekeken naar de invloed van relatieve luchtvochtigheid op de ontwikkeling van Pseudomonas cattleyae. Uit de resultaten blijkt dat een relatieve luchtvochtigheid van 90% de bacterieverspreiding enorm stimuleert en dat de mate van de aantasting ook veel ernstiger is dan bij lagere relatieve luchtvochtigheden. Een relatieve luchtvochtigheid van 75% toont geen extra verspreiding van Pseudomonas cattleyae ten opzichte van de verspreiding in een kascompartiment waar een relatieve luchtvochtigheid van continu 60% wordt gerealiseerd. Met deze kennis kan bij de teelt Phalaenopsis een energiebesparing worden gerealiseerd. In dit onderzoek zijn ook de effecten van gietwaterbehandelingen op de verspreiding van Pseudomonas cattleyae bekeken. Uit de resultaten komt een behandeling met waterstofperoxide van 20 ppm als beste naar voren. Deze behandeling is beter dan de onbehandelde controle en de andere behandelingen. Dit onderzoek heeft geleid tot nieuwe inzichten in de verspreiding en optimale groeicondities van de bacterie, maar geeft ook weer aanleiding tot het stellen van nieuwe vragen. Vragen over andere doseringen en nieuwe gietbehandelingen, maar ook over de uiterste grens voor de relatieve luchtvochtigheid waarbij geen extra verspreiding optreedt zullen in een vervolgonderzoek moeten worden onderzocht. Abstract Phalaenopsis growers suffer from mayor losses up to 20% due to bacterial s

Pollen of the European and Asian white birch (Betula pendula and B. platyphylla) causes hay fever in humans. The allergenic potency of other birch species is largely unknown. To identify birch trees with a reduced allergenicity, we assessed the immunochemical characteristics of 15 species and two hybrids, representing four subgenera within the genus Betula, while focusing on the major pollen allergen Bet v 1. Antigenic and allergenic profiles of pollen extracts from these species were evaluated by SDS-PAGE and Western blot using pooled sera of birch-allergic individuals. Tryptic digests of the Bet v 1 bands were analyzed by LC-MSE to determine the abundance of various Bet v 1 isoforms. Bet v 1 was the most abundant pollen protein across all birch species. LC-MSE confirmed that pollen of all species contained a mixture of multiple Bet v 1 isoforms. Considerable differences in Bet v 1 isoform composition exist between birch species. However, isoforms that are predicted to have a high IgE-reactivity prevailed in pollen of all species. Immunoblotting confirmed that all pollen extracts were similar in immune-reactivity, implying that pollen of all birch species is likely to evoke strong allergic reactions.

The development of genetically modified (GM) foods with benefits for consumers may be more acceptable than GM foods with benefits that accrue to industry or producers. The Santana apple is a novel hypoallergenic product suitable for many apple allergic consumers with mild symptomology. The Santana also needs fewer pesticides to be applied in production. A survey was conducted among consumers who bought the Santana in a large-scale “sales pilot”. The Santana was perceived to be beneficial by many apple allergic consumers. Non-allergic consumers were less positive about genetically modified hypoallergenic apples. Overall, traditional breeding was the preferred production strategy, although acceptance of genetic modification as a process did increase with increasing perceived personal benefit associated with products, in particular those which were “medically-related”, or perceived to reduce allergic reactions. Consumer preferences for reduced pesticide usage were also found, although this was more contingent on type of production processes applied.

Background: Epidemiologic studies reveal a dramatic increase in allergies in the last decades. Air pollution is considered to be one of the factors responsible for this augmentation. The aim of this study was to analyze the impact of urbanization on birch pollen. The birch pollen proteome was investigated in order to identify differences in protein abundance between pollen from rural and urban areas. The allergenicity of birch pollen from both areas was evaluated by assessing its chemotactic potency as well as its protein and allergen contents. Methods: Difference gel electrophoresis (DIGE) was used to analyze the pollen proteome. The chemotactic activity of aqueous pollen extracts was determined by migration assays of human neutrophils. Results: DIGE revealed 26 differences in protein spot intensity between pollen from urban and rural areas. One of these proteins was identified by de novo sequencing as the 14-3-3 protein, which resembles a stress-induced factor in other plant species. Furthermore, extracts from pollen collected in urban areas had higher chemotactic activity on human neutrophils compared to pollen from rural sites. Conclusions: The present study points to an impact of air pollution on allergen carrier proteome and release of chemotactic substances. The increment in proinflammatory substances such as pollen-associated lipid mediators might contribute to the described urban-rural gradient of allergy prevalence. Furthermore, our study suggests that allergenicity is determined by more than the sole allergen content.

Pepinomozaïkvirus is een mechanisch overdraagbaar virus. Het tegengaan van besmettingen met dit virus blijkt in de praktijk bijzonder lastig. Naast het aanhouden van strikte hygiëne vormt de toepassing van cross-protectie een alternatieve strategie. Daarbij veronderstelt met dan besmetting met zwakke virusisolaten (zwakke stammen) de gevolgen van een besmetting met agressieve isolaten onderdrukt. In 2005 en 2006 is in kasproeven aangetoond dat cross-protectie met de isolaten V1 of 1066 werkt tegen isolaten van de Europese (EU) stam van pepinomozaïkvirus. Kleinschalige preoven uit 2008 suggereerden echt dat de zwakke isolaten V1 en 1066 niet in staat zijn om beschrming met nieuwe varianten die tot de Chili-2 stam (CH-2) behoorden, waren doorbraakverschijnselen zichtbaar. Een zwak isolaat da behoorde tot deze Ch-2 stam bood wel bescherming onder deze omstandigheden, maar was minder zwak in zijn symptomen dan V1 en 1066. In de proeven uit 2008 is vanwege de looptijd van de proef alleen gekeken naar het optreden van bladsymptomen.

Pepinomozaïekvirus (PepMV) heeft zich sinds de eerste verschijning sterk verspreid en zorgt nu al een decennium voor flinke problemen in de tomatenteelt. In de loop der tijd zijn diverse onderzoeken uitgevoerd naar dit virus. Op dit moment is de toepassing van strikte hygiënemaatregelen de enige optie waarvan met zekerheid vaststaat dat het helpt om dit virus in te perken. Cross-protectie blijkt slechts onder bepaalde omstandigheden te werken

De laatste jaren nemen de problemen en economische schade door het tomatenbronsvlekkenvirus (TSWV) toe binnen de paprikateelt. De Californische trips is in Nederland waarschijnlijk de voornaamste vector van dit virus. In 2005 veroorzaakte TSWV problemen op meerdere paprikabedrijven, terwijl in 2007 enkele zeer ernstige besmettingen optraden. De vraag is welke factoren deze recente toename veroorzaken en hoe men besmetting kan voorkomen

Binnen de Hortensiateelt worden planten aangetroffen met ziekteverschijnselen die wijzen op besmetting met een fytoplasma. Aangetaste Hortensia's hebben groene bloemen, er ontstaan scheuten vanuit de bloemdelen en de planten blijven achter in groei zodra de vegetatieve fase van de plant inzet. Doel van het in dit rapport beschreven onderzoek was om vast te stellen op welke schaal besmetting met fytoplasma in Hortensia optreedt in Nederland en om aanknopingspunten te vinden om besmetting te voorkomen of in te perken.

Bij een zevental tomatentelers die absoluut vrij wilden blijven van een besmetting met het pepinomozaïekvirus is de teelt gevolgd en begeleid. Deze telers namen tevens deel aan een praktijknetwerk waarin ervaringen werden uitgewisseld.

Het Pepinomozaïekvirus (PepMV) is een mechanisch overdraagbaar virus. Het tegengaan van besmetting is in de praktijk zeer lastig. Naast het aanhouden van strikte hygiëne is de toepassing van cross-protectie een alternatieve strategie. Daarbij veronderstelt men dat besmetting met milde virusvarianten (zwakke stammen) de gevolgen van een besmetting met agressieve isolaten ondedrukt. Eerder is aangetoond dat cross-protectie met V1 of 1066 tegen de Europese tomatenstam van PepMV werkt. De doelstelling van dit onderzoek was om te bepalen of zwakke stammen in staat zijn om te beschermen tegen nieuwe agressievere isolaten van PepMV.

Recent is een nieuw hygiëneprotocol voor komkommer verschenen waarin de belangrijkste virussen zijn weergegeven. Daarnaast is ook een tipkaart verschenen wat een verkorte versie is van dit protocol. In het protocol neemt komkommerbontvirus een prominente plaats in. Per teeltfase staan allerlei maatregelen om de kas tijdens de teeltwisseling grondig te reinigen. Belangrijk is om al het organisch materiaal uit de kas te verwijderen en daarna goed schoon te maken. Voorkom dat het virus van buitenaf het bedrijf binnen komt door bijvoorbeeld aanneemploegen of loonwerkers

In 2008 waren er weinig problemen met trips in paprika en bleven de problemen door tomatenbronsvlekkenvirus beperkt door toepassing van hygiënemaatregelen tijdens de teeltwisseling, de inzet van biologische bestrijders en het consequent verwijderen van virusplanten. Het onderzoek geeft nog geen uitsluitsel over de ernst van de problemen in jaren met veel trips. Daarbij spelen virusbronnen buiten de kas mogelijk een rol. Komende jaren kan dit virus dus opnieuw op grotere schaal opduiken

Background - Bet v 1 is an important cause of hay fever in northern Europe. Bet v 1 isoforms from the European white birch (Betula pendula) have been investigated extensively, but the allergenic potency of other birch species is unknown. The presence of Bet v 1 and closely related PR-10 genes in the genome was established by amplification and sequencing of alleles from eight birch species that represent the four subgenera within the genus Betula. Q-TOF LC-MSE was applied to identify which PR-10/Bet v 1 genes are actually expressed in pollen and to determine the relative abundances of individual isoforms in the pollen proteome. Results - All examined birch species contained several PR-10 genes. In total, 134 unique sequences were recovered. Sequences were attributed to different genes or pseudogenes that were, in turn, ordered into seven subfamilies. Five subfamilies were common to all birch species. Genes of two subfamilies were expressed in pollen, while each birch species expressed a mixture of isoforms with at least four different isoforms. Isoforms that were similar to isoforms with a high IgE-reactivity (Bet v 1a =PR-10.01A01) were abundant in all species except B. lenta, while the hypoallergenic isoform Bet v 1d (=PR-10.01B01) was only found in B. pendula and its closest relatives. Conclusions - Q-TOF LC-MSE allows efficient screening of Bet v 1 isoforms by determining the presence and relative abundance of these isoforms in pollen. B. pendula contains a Bet v 1-mixture in which isoforms with a high and low IgE-reactivity are both abundant. With the possible exception of B. lenta, isoforms identical or very similar to those with a high IgE-reactivity were found in the pollen proteome of all examined birch species. Consequently, these species are also predicted to be allergenic with regard to Bet v 1 related allergies

In dit rapport wordt ingegaan op de probleemanalyse van virussen in komkommer, de herkenning van komkommerbontvirus, komkommermozaïekvirus, tabaksnecrosevirus, meloenennecrosevirus, pseudo-slavergelingsvirus, courgettegeelmozaïekvirus, watermeloenenmozaïekvirus en komkommerblekevruchtenviroïde en de te treffen hygiënemaatregelen

Nederland had twee jaar geleden de primeur: Santana, een hyperallergeen appelras voor mensen met appelallergie. Wageningen UR heeft de ervaringen van de consumenten over 2006 en 2007 onderzocht. De vermindering van de allergische reactie is ongeveer volgens verwachting en de tevredenheid blijkt hoog te zijn

Allergic diseases, such as hay fever and food allergy, affect an increasing part of the population in Westernized countries and have a negative impact on the patient's quality of life. Allergy prevention measures that focus on reducing the allergenic load are currently developed, and these may include the use of genetic modification of allergenic plants. Such developments should take societal concerns about genetic modification into account. We examined the attitude of allergic and non-allergic respondents towards applications of genetic modification for allergy prevention in one food allergy application (apple) and two hay fever applications (birch, grass). Attitude towards genetic modification was described in terms of 'benefits' and 'rejection factors.' We found that respondents suffering from self-reported allergy perceived greater benefits associated with the birch application as compared to non-sufferers. The perceived benefits increased with an increasing impact of allergic complaints on quality of life. No differences were found between sufferers and non-sufferers for the food allergy application. The impact of perceived benefits on acceptance was larger than that of rejection factors. This supports the idea that acceptance of genetic modification is primarily a function of perceived personal benefit. Novel genetically modified products that are perceived to be beneficial by some consumers may consequently experience an increased consumer acceptance

The genus Betula comprises various species in boreal and temperate climate zones of the Northern Hemisphere. The taxonomy of Betula is controversial and complicated by parallel evolution of morphological traits, polyploidization events, and extensive hybridization and introgression among species. Multilocus molecular data from AFLPs were used to provide phylogenetic information. A large number of polymorphic markers (321 variable bands) were produced in 107 Betula accessions from 23 species and 11 hybrids. The AFLP results were largely congruent with the results from previously examined nuclear DNA markers. Four distinct subgenera were identified within the genus Betula. These subgenera were partly in disagreement with the traditional (but disputed) division of the genus. In addition, the results indicated several groups of conspecific taxa. The majority of the species fell within subgenus Betula and shared a high degree of similarity with B. pendula. All hybrids were associated with this group, and the AFLP data contained signals on putative parents for some of the interspecific hybrids. Subgenus Chamaebetula and part of the Neurobetula species should be merged with Betula. The subgenera Betulenta, Betulaster, and the remaining part of Neurobetula are distinct and well supported. Although our results indicate that four major taxonomic groups can be recognized within the genus Betula, the relationship between them remains unclear. This may be due to the occurrence of hybridization and introgression, which would have a homogenizing effect on the relationships between species. Naturally occurring Betula species of hybrid origin may explain the low bootstrap values within the Betula clade.

Background - Bread wheat (Triticum aestivum) is an important staple food. However, wheat gluten proteins cause celiac disease (CD) in 0.5 to 1% of the general population. Among these proteins, the a-gliadins contain several peptides that are associated to the disease. Results - We obtained 230 distinct a-gliadin gene sequences from severaldiploid wheat species representing the ancestral A, B, and D genomes of the hexaploid bread wheat. The large majority of these sequences (87%) contained an internal stop codon. All a-gliadin sequences could be distinguished according to the genome of origin on the basis of sequence similarity, of the average length of the polyglutamine repeats, and of the differences in the presence of four peptides that have been identified as T cell stimulatory epitopes in CD patients through binding to HLA-DQ2/8. By sequence similarity, a-gliadins from the public database of hexaploid T. aestivum could be assigned directly to chromosome 6A, 6B, or 6D. T. monococcum (A genome) sequences, as well as those from chromosome 6A of bread wheat, almost invariably contained epitope glia-a9 and glia-a20, but never the intact epitopes glia-a and glia-a2. A number of sequences from T. speltoides, as well as a number of sequences fromchromosome 6B of bread wheat, did not contain any of the four T cell epitopes screened for. The sequences from T. tauschii (D genome), as well as those from chromosome 6D of bread wheat, were found to contain all of these T cell epitopes in variable combinations per gene. The differences in epitope composition resulted mainly from point mutations. These substitutions appeared to be genome specific. Conclusion - Our analysis shows that a-gliadin sequences from the three genomes of bread wheat form distinct groups. The four known T cell stimulatory epitopes are distributed non-randomly across the sequences, indicating that the three genomes contribute differently to epitope content. A systematic analysis of all known epitopes in g

Seasonal allergic rhinitis is a widespread disorder in westernized countries. It has a strong negative impact on the patient¿s health-related quality of life and is accompanied by considerable medical and economic costs. Currently, the socioeconomic interest in prevention is growing. Reducing or avoiding allergen exposure may result in a significant reduction of sensitization and mitigation of allergic complaints, and this reduction is in addition to existing medical prevention strategies. It will require good communication to (potential) patients on the importance and possibilities for reducing the contact with allergenic pollen. Longterm pollen monitoring and forecasts of the flowering period of allergenic plants are important tools in this respect. Reducing the allergenic load may prove an alternative prevention strategy. Pollen sources are heterogeneously distributed throughout the landscape and may be avoided or selectively removed. The use of selection, conventional breeding strategies or genetic modification may reduce the allergenicity of the pollen sources. Strategies that involve genetic modification are, however, likely to raise some public concern and acceptability of these strategies has to be considered. Keywords: seasonal allergic rhinitis; allergy prevention; pollen allergens; crossreactivity; phenology; allergenicity; risk analysis; public concern

Background: Pollen of the European white birch (Betula pendula, syn. B. verrucosa) is an important cause of hay fever. The main allergen is Bet v 1, member of the pathogenesis-related class 10 (PR-10) multigene family. To establish the number of PR-10/Bet v 1 genes and the isoform diversity within a single tree, PCR amplification, cloning and sequencing of PR-10 genes was performed on two diploid B. pendula cultivars and one interspecific tetraploid Betula hybrid. Sequences were attributed to putative genes based on sequence identity and intron length. Information on transcription was derived by comparison with homologous cDNA sequences available in GenBank/EMBL/DDJB. PCR-cloning of multigene families is accompanied by a high risk for the occurrence of PCR recombination artifacts. We screened for and excluded these artifacts, and also detected putative artifact sequences among database sequences. Results: Forty-four different PR-10 sequences were recovered from B. pendula and assigned to thirteen putative genes. Sequence homology suggests that three genes were transcribed in somatic tissue and seven genes in pollen. The transcription of three other genes remains unknown. In total, fourteen different Bet v 1-type isoforms were identified in the three cultivars, of which nine isoforms were entirely new. Isoforms with high and low IgE-reactivity are encoded by different genes and one birch pollen grain has the genetic background to produce a mixture of isoforms with varying IgE-reactivity. Allergen diversity is even higher in the interspecific tetraploid hybrid, consistent with the presence of two genomes. Conclusions: Isoforms of the major birch allergen Bet v 1 are encoded by multiple genes, and we propose to name them accordingly. The present characterization of the Bet v 1 genes provides a framework for the screening of specific Bet v 1 genes among other B. pendula cultivars or Betula species, and for future breeding for trees with a reduced allergenicity. Investig