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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.

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.

Wageningen University & Research centre heeft samen met het Universitair Medisch Centrum Utrecht en Universitair Medisch Centrum Groningen een hypoallergene appel geïdentificeerd, de Santana, die sinds 2006 als zodanig verkrijgbaar is in de supermarkt. In 2011 is hier het ras Elise met een ander smaakprofiel en andere bewaareigenschappen als nieuwe hypoallergene appel bijgekomen. Hiermee is het aanbod verbreed. Daarnaast zijn appels genetisch gemodificeerd (GM) om te onderzoeken of de techniek van ‘gene silencing’ geschikt is om het meest voorkomende allergeen in appel, Mal d 1, uit te schakelen. Deze GM-appels zijn niet bestemd voor consumptie. Ten slotte is met een combinatie van DNA-onderzoek en veredelingsonderzoek een mogelijk laagallergene eiwitvariant van Mal d 1 geïdentificeerd die slechts één aminozuur verschilt van een hoogallergene variant. De kennis uit dit onderzoek wordt benut om de ontwikkeling van hypoallergene appelrassen en andere hypoallergene plantaardige producten te versnellen en daarmee de kwaliteit van leven van de allergische consument te verbeteren.

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 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.

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

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.

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

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.

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.

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.

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

Allergic diseases, such as hay fever and food allergy, affect a substantial part of the population in westernized countries. Pollen of the European white birch (Betula pendula) is a considerable cause of hay fever (seasonal allergic rhinitis) in northern and central Europe. The major birch pollen allergen is Bet ν 1, which is the conventional allergen name for the birch pollen proteins of a large group of proteins otherwise known as PR-10 proteins. Individuals that suffer from birch pollen allergy are particularly prone to develop Oral Allergy Syndrome (OAS) due to the occurrence of an IgE-mediated cross-reaction between Bet ν 1 and PR-10 proteins in various plant foods. The high prevalence of apple allergy among hay fever sufferers is a good example of OAS. Allergic diseases can be severe for patients and have considerable medical and economical costs as well. Consequently, prevention of birch pollen allergy and OAS would contribute to an improvement of the quality of life of many patients. This thesis examines the feasibility of strategies that are directed towards development of hypoallergenic (= having a reduced allergenicity) birch trees or plant foods in order to alleviate Bet ν 1 [PR-10]- associated complaints. When the development of hypoallergenic products involves application of genetic modification (GM), societal concerns about this technology should be taken into account. The attitude towards hypoallergenic products developed by GM was examined in the survey that is described in Chapter 2. This study differentiated between patients and non-patients. Attitude towards GM was measured for two applications directed against hay fever (hypoallergenic birch and grass) and one application directed against food allergy (hypoallergenic apple). Attitude was described in terms of two constructs that were labelled as 'benefits' and 'rejection factors'. Hay fever sufferers perceived greater 'benefits' associated with application of GM to develop hypoallergenic birch trees as compared to non-sufferers. The perceived 'benefits' increased with a higher self-reported impact of hay fever on quality of life. No attitudinal differences were observed between sufferers and non-sufferers for the attitudinal construct 'rejection factors'. Furthermore, the impact of perceived 'benefits' on acceptance of GM was larger than the impact of 'rejection factors'. The perceptions of 'benefits' were further explored in Chapter 3. Here, the attitude towards hypoallergenic apples was examined in a survey in which consumers rate a set of apple profiles that varied in the breeding method that was applied during development (GM vs. traditional breeding), in pesticide usage, and in the degree of allergenicity. Acceptance of hypoallergenic apples was high among all consumers, also when GM was involved in their development. Acceptance of hypoallergenic products was higher among consumers with an apple allergy, presumably because they find a personal 'benefit' associated with these products. Novel GM products that are recognised as beneficial by some consumers may consequently experience an increased acceptance. However, both Chapter 2 and 3 indicated a clear consumer preference for traditional breeding over breeding by GM for the development of hypoallergenic birch trees or food products. Approaches which focus on traditional breeding should thus be explored first. Chapter 3 also evaluated appreciation of the hypoallergenic apple cultivar Santana, which was introduced in shops in a large-scale sales pilot labelled as 'suitable for individuals suffering from mild apple allergy' in 2006. A survey among consumers that bought the Santana measured the self-reported response to this apple. Almost half (42%) of the apple allergic consumers had no allergic reaction at all after eating the Santana. Most (96%) consumers who did experience an allergic reaction reported the symptoms as minor. The self-reported severity of the apple allergy, the occurrence of other fruit allergies, and age were associated with the occurrence of an allergic reaction to the Santana. Overall, the Santana was valued positively by the majority of apple allergic consumers, regardless of whether these consumers could eat the apple without experiencing an allergic reaction. Development of hypoallergenic foods such as Santana may therefore contribute to food allergy management, although variation among individual consumers in the allergic response to hypoallergenic products should be taken into account when developing and marketing such products. A prerequisite for designing strategies for selection and breeding of hypoallergenic birch trees is knowledge on diversity of Bet ν 1 genes and on allergenicity of the protein variants (=isoforms) that are encoded by these genes. Chapter 4 describes a study on the variation of Bet ν 1 isoforms in .the most common birch species in Europe, Betula pendula. PR-10 sequences from three B. pendula cultivars were amplified, cloned and sequenced. Forty-four unique PR-10 sequences were recovered from B. pendula and these were assigned to thirteen putative genes based on sequence identity and intron length. Information on gene transcription was inferred from a comparison with existing mRNA sequences and suggested that seven of these genes are transcribed in pollen. Bet ν 1 isoforms are known to vary in IgE-reactivity. The study in Chapter 4 showed that isoforms with high and low IgE-reactivity are encoded by different genes. Thus, one birch pollen grain has the genetic background to produce a mixture of isoforms with varying IgE-reactivity. The sequence of one of the isoforms with a high IgE-reactivity was present in all examined B. pendula trees. The search for hypoallergenic birch trees was, therefore, expanded to other Betula species. The selection of a representative set of species which cover variation among Betula species requires knowledge on phylogenetic relationships within the genus Betula. Chapter 5 describes a study on the reconstruction of the phylogeny of this genus using multilocus data from AFLP markers. The taxonomy of the genus Betula is complicated by the occurrence of parallel evolution of morphological traits, of polyploidisation events, and of extensive hybridisation among species. A large number of polymorphic AFLP markers (321 variable bands) were produced in 107 Betula accessions from 23 species and 11 hybrids. The analysis identified four distinct groups within the genus. These groups are partly in disagreement with the traditional, but disputed, division of the genus. The majority of the species and all hybrids fell within subgenus Betula and are thus closely related to B. pendula. Subgenus Chamaebetula and part of the Neurobetula species should be merged with subgenus Betula. Apart from subgenus Betula, the subgenera Betulenta, Betulaster, and the remaining part of Neurobetula formed distinct and well-supported groups and should thus be maintained. The results from the AFLP study are to a large extent congruent with results from previous studies that made use of molecular (sequence) data. The allergenic potency of Betula species other than B. pendula is described in Chapter 6 in which the PR-10 genes from eight birch species are cloned and sequenced. These species represent the various groups that were previously identified in the genus Betula. In total, 134 unique PR-10 sequences were recovered, including both sequences with a full open reading frame and pseudogenes. Sequences were attributed to putative genes, which could, in turn, be subdivided into seven subfamilies. Five subfamilies were common to all birch species. Q-TOF LC-MSE was applied to detect peptide fragments of Bet ν 1 that are unique for particular isoforms, in order to identify which PR-10 genes are expressed in pollen. The relative abundance of individual isoforms in the pollen proteome was also determined by Q-TOF LC-MSE. Each of the five examined birch species expressed a mixture of isoforms with at least 4-5 different isoforms. Both isoforms with a high and low IgE-reactivity were abundant in the Bet ν 1 mixture of B. pendula. The other birch species lacked Bet ν 1 isoforms that are similar to known isoforms with a low IgE-reactivity, but isoforms that are similar to known isoforms with a high IgE-reactivity were abundant in all species except B. lenta. In Chapter 7, the antigenic and allergenic profiles of pollen extracts from twenty-four different birch trees were determined by SDS-PAGE and Western blotting. Fifteen different Betula species were examined, covering all previously identified subgenera/groups in the genus Betula. The major birch allergen Bet ν 1 was an abundant protein in all examined pollen extracts. Immune-reactivity of the extracts was tested using a pool of sera that were obtained from birch pollen allergic patients. A strong 17 kDa band, representing Bet ν 1, was recognized by the serum pool in all pollen extracts. The degree of immune-reactivity correlated well with the total amount of Bet ν 1 in the extract, which varied from 44% to 61% of the total protein content. Pollen extracts from different birch trees varied in the total protein content, presumably the result of variation in pollen quality due to pollen rupture and varying hydration during the extraction. Bet ν 1 isoforms in the pollen of eleven Betula species were subsequently digested with trypsin and the resulting fragments were analyzed and quantified by Q-TOF LC-MSE. Peptides that contained amino acid residues that are associated with high IgE-reactivity were detected in all examined species, and were abundant as well. Differences between Betula species in the relative presence of these amino acid residues were small. As a consequence, differences in allergenicity between birch trees are probably far too small to have clinical relevance, implying that all examined Betula species will be highly allergenic. The research presented here did not identify any birch trees in which Bet ν 1 variants with a high IgE-reactivity are reduced in abundance or are absent. Development of hypoallergenic birch trees thus must rely on other approaches, such as selection or introduction of male sterility (trees that do not produce male catkins were observed during the study), or the application of RNAi to silence the Bet ν 1 genes in pollen. Also, the conducted research showed that acceptance of hypoallergenic GM products is quite high, particularly for allergic sufferers who were allergic to the product being modified. This supports the hypothesis that consumer attitude towards GM is partly driven by recognition of specific and personally relevant benefits. The hypoallergenic apple cultivar Santana, which was developed by selection and not by GM, was well received by allergic consumers, indicating that there is a market for hypoallergenic products.

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

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

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