Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Synergy in efficacy of fungal entomopathogens and permethrin against West African insecticide-resistant Anopheles gambiae mosquitoes
    Farenhorst, M. ; Knols, B.G.J. ; Thomas, M.B. ; Howard, A.F.V. ; Takken, W. ; Rowland, M. ; N'Guessan, R. - \ 2010
    PLoS ONE 5 (2010)8. - ISSN 1932-6203 - 10 p.
    metarhizium-anisopliae - culex-quinquefasciatus - malaria mosquitos - pyrethroid resistance - infection - vectors - deuteromycotina - biopesticides - coleoptera - knockdown
    Background Increasing incidences of insecticide resistance in malaria vectors are threatening the sustainable use of contemporary chemical vector control measures. Fungal entomopathogens provide a possible additional tool for the control of insecticide-resistant malaria mosquitoes. This study investigated the compatibility of the pyrethroid insecticide permethrin and two mosquito-pathogenic fungi, Beauveria bassiana and Metarhizium anisopliae, against a laboratory colony and field population of West African insecticide-resistant Anopheles gambiae s.s. mosquitoes. Methodology/Findings A range of fungus-insecticide combinations was used to test effects of timing and sequence of exposure. Both the laboratory-reared and field-collected mosquitoes were highly resistant to permethrin but susceptible to B. bassiana and M. anisopliae infection, inducing 100% mortality within nine days. Combinations of insecticide and fungus showed synergistic effects on mosquito survival. Fungal infection increased permethrin-induced mortality rates in wild An. gambiae s.s. mosquitoes and reciprocally, exposure to permethrin increased subsequent fungal-induced mortality rates in both colonies. Simultaneous co-exposure induced the highest mortality; up to 70.3±2% for a combined Beauveria and permethrin exposure within a time range of one gonotrophic cycle (4 days). Conclusions/Significance Combining fungi and permethrin induced a higher impact on mosquito survival than the use of these control agents alone. The observed synergism in efficacy shows the potential for integrated fungus-insecticide control measures to dramatically reduce malaria transmission and enable control at more moderate levels of coverage even in areas where insecticide resistance has rendered pyrethroids essentially ineffective.
    Telers willen nog meer kennis van Botrytis : Discussie
    Bezemer, Jos ; Wageningen UR Glastuinbouw, - \ 2010
    Onder Glas 7 (2010)3. - p. 25 - 27.
    tuinbouwbedrijven - teeltsystemen - botrytis - deuteromycotina - plantenziekteverwekkende schimmels - bestrijdingsmethoden - schimmelbestrijding - groenteteelt - tomaten - solanum lycopersicum - glastuinbouw - kennisoverdracht - groenten - market gardens - cropping systems - botrytis - deuteromycotina - plant pathogenic fungi - control methods - fungus control - vegetable growing - tomatoes - solanum lycopersicum - greenhouse horticulture - knowledge transfer - vegetables
    Botrytis is een lastige klant. Over met name de financiële kant van de maatregelen tegen deze schimmel, de samenhang met bladrandjes en de tegenstelling tussen lagere energiekosten en het grotere risico op Botrytis als gevolg daarvan is nog onvoldoende bekend. Meer kennis van deze onderwerpen zal telers helpen deze schimmel effectiever aan te pakken. Dat bleek in een discussie tussen telers, beleidsmakers, onderzoekers en dienstverleners.
    Teler staat niet met lege handen tegenover Botrytis (interview met Leo Marcelis en Jantine Hofland)
    Bezemer, J. ; Marcelis, L.F.M. ; Hofland-Zijlstra, J.D. - \ 2010
    Onder Glas 7 (2010)2. - p. 36 - 37.
    tuinbouw - botrytis - deuteromycotina - microklimaat - omgevingstemperatuur - schimmelziekten - groenteteelt - vochtgehalte - luchtstroming - antagonisten - schimmelantagonisten - glastuinbouw - sierteelt - groenten - horticulture - botrytis - deuteromycotina - microclimate - environmental temperature - fungal diseases - vegetable growing - moisture content - air flow - antagonists - fungal antagonists - greenhouse horticulture - ornamental horticulture - vegetables
    Botrytis kan in heel wat gewassen fikse problemen veroorzaken. Omdat de sporen in een vochtige omgeving gaan kiemen, is een droog microklimaat de beste remedie. Maar het droogstoken van een hele kas is kostbaar. Met buitenluchtaanzuiging is een betere en energiezuinigere vochtbeheersing te realiseren. Het gewas voldoende open houden, blad snijden en luchtcirculatie zijn manieren om het gewenste microklimaat te bereiken. Antagonisten kunnen Botrytis preventief tegengaan en zijn een alernatief voor chemische middelen, terwijk bestuiving met oxidatieve zoeten of bestrlaing met UV-C-licht met namen in de na-oogst effectief kunnen zijn
    Vluchtige stoffen als instrument voor monitoring gewas
    Jansen, R.M.C. ; Heuvelink, E. ; Kierkels, T. - \ 2010
    Onder Glas 7 (2010)2. - p. 10 - 11.
    vruchtgroenten - solanum lycopersicum - tomaten - geurstoffen - botrytis - deuteromycotina - monitoring - glastuinbouw - groenten - fruit vegetables - solanum lycopersicum - tomatoes - odours - botrytis - deuteromycotina - monitoring - greenhouse horticulture - vegetables
    Planten stoten een groot aantal verschillende vluchtige stoffen uit. Die zeggen iets over de toestand van de plant. Met sensoren zijn ze te meten. In de toekomst kun je daarop wellicht monitoren. Wageningen UR Glastuinbouw is erin geslaagd aan de hand van zo’n vluchtige stof een botrytisaantasting in een tomatengewas te detecteren, voordat die zichtbaar is. Het is de bedoeling de methode op te schalen tot praktijkniveau
    Botrytis in tomaat: wat aanpakken en hoe?
    Meijer, Rob - \ 2009
    market gardens - vegetable growing - tomatoes - fruit vegetables - botrytis - deuteromycotina - pest control - infections - disease prevention - genetic control - pesticides - greenhouse horticulture
    Preventive and curative control of Botrytis stem infestation in tomato using chemical and non-chemical measures
    Hofland-Zijlstra, J.D. ; Köhl, J. ; Böhne, S. - \ 2009
    Gewasbescherming 40 (2009)5. - ISSN 0166-6495 - p. 261 - 261.
    tuinbouw - teelt onder bescherming - kassen - botrytis - deuteromycotina - aantasting - tomaten - plantenziekteverwekkende schimmels - gewasbescherming - glastuinbouw - horticulture - protected cultivation - greenhouses - botrytis - deuteromycotina - infestation - tomatoes - plant pathogenic fungi - plant protection - greenhouse horticulture
    Every year, Botrytis stem infestation is responsible for considerable crop losses in greenhouse tomatoes. Wounds produced by the common practice of pulling of old leaves frequently are the main infection site for the fungus. No effective control agents for curing infected plants are available. In 2008, WUR Greenhouse horticulture performed field tests on a mature tomato crop with two synthetic fungicides (imazalil and enapyrim), two fungal antagonists (Trichoderma harzianum and Gliocladium catenulatum) and the enzymatic product Enzicur (lactoperoxidase activity)
    Beheersing dode bloemknoppen bij peer binnen bereik
    Wenneker, M. ; Anbergen, R.H.N. ; Joosten, N.N. - \ 2008
    De Fruitteelt 98 (2008)19. - ISSN 0016-2302 - p. 9 - 9.
    boomgaarden - fruitteelt - fruitgewassen - peren - alternaria - deuteromycotina - plantenziekteverwekkende schimmels - bestrijdingsmethoden - spuiten - gewasbescherming - toelating van bestrijdingsmiddelen - orchards - fruit growing - fruit crops - pears - plant pathogenic fungi - control methods - spraying - plant protection - authorisation of pesticides
    Uit PPO-onderzoek blijkt dat Alternaria de primaire veroorzaker is van dode bloemknoppen bij peer. De mate van aantasting verschilt per perceel en per jaar. Met de toelating van Switch is een directe bestrijding van Alternaria mogelijk geworden
    Comparative analysis of genetic incompatibility in Aspergillus niger and Podospora anserina
    Pal, K. - \ 2007
    Wageningen University. Promotor(en): Rolf Hoekstra, co-promotor(en): Fons Debets. - [S.l.] : S.n. - ISBN 9789085046554 - 135
    aspergillus niger - deuteromycotina - pezizomycotina - incompatibiliteit - genetische analyse - aspergillus niger - deuteromycotina - pezizomycotina - incompatibility - genetic analysis
    Reproduction is of crucial importance for living organisms, from bacteria to humans. Except for mammals and birds, both sexual and asexual reproduction is known almost at every level of thephylogenetictree. A special case of asexual reproduction in filamentous fungi is the so calledparasexualcycle, whenhyphaeof different individuals fuse and the genetic material of different origin can be mixed. The black mouldAspergillusniger is a versatile organism used in industry and sometimes found as opportunistic pathogen. This is an asexual species, and most of the natural isolates are unable to undergo theparasexualcycle, in other words strains are (vegetatively) incompatible. Unlike the A.niger thePodosporaanserina is a strictly sexual species and used as a model organism for studying features ofparasexualcycle. In this study the genetic background of vegetative incompatibility and remnants of presumed ancient sexual stage of A.niger and features of vegetative incompatibility in P.anserina were investigated and compared.
    Omvallers bij pioen effectief te bestrijden
    Wubben, J.P. ; Slootweg, G. ; Janse, J. - \ 2006
    Gewasnieuws Zomerbloemen 9 (2006)1. - p. 3 - 3.
    paeonia - overblijvende planten - plantenziekteverwekkende schimmels - botrytis - deuteromycotina - pesticiden - toepassing - toepassingsdatum - paeonia - perennials - plant pathogenic fungi - botrytis - deuteromycotina - pesticides - application - application date
    Omvallers in pioenroos door botrytis zijn goed te voorkomen, blijkt uit onderzoek van PPO Glastuinbouw. Daarvoor is de effectiviteit van een aantal middelen onderzocht en het tijdstip van toediening
    Phylogeny and taxonomy of Phaeoacremonium and its relatives
    Mostert, L. - \ 2006
    Wageningen University. Promotor(en): Pedro Crous, co-promotor(en): E.C.A. Abeln. - [S.l.] : S.n. - ISBN 9789085044604 - 249
    diaporthales - pezizomycotina - deuteromycotina - fylogenie - taxonomie - phaeohyphomycose - humane ziekten - medische mycologie - determinatietabellen - plantenziekteverwekkende schimmels - diaporthales - pezizomycotina - deuteromycotina - phylogeny - taxonomy - keys - phaeohyphomycosis - human diseases - medical mycology - plant pathogenic fungi
    Species of Phaeoacremonium are known vascular plant pathogens causing wilt and dieback of woody hosts.  The most prominent diseases in which they are involved are Petri disease and esca, which occur on grapevines and are caused by a complex of fungi, including Phaeomoniella chlamydospora and several species of Phaeoacremonium . Various Phaeoacremonium species are also opportunistic on humans, where they are known to cause phaeohyphomycosis. 

    The genus Togninia was confirmed as the teleomorph of Phaeoacremonium by means of morphology, sexual compatibility, and DNA phylogeny. Subsequently, the genus Togninia was monographed along with its Phaeoacremonium anamorphs. Ten species of Togninia and 22 species of Phaeoacremonium were treated. Several new species of Togninia were found during the course of the study, namely T. argentinensis , T. austroafricana , T. krajdenii , T.parasitica , T.rubrigena and T. viticola . New species of Phaeoacremonium includePm. alvesii, Pm. amstelodamense,Pm. argentinense ,Pm. australiense,Pm. austroafricanum, Pm. griseorubrum,Pm.krajdenii,Pm. novae-zealandiae , Pm . iranianum ,Pm. scolyti, Pm. sphinctrophorum,Pm.subulatum,Pm. tardicrescens,Pm . theobromatisandPm. venezuelense . Species were identified based on their cultural and morphological characters, supported by DNA data derived from partial sequences of the actin and β-tubulin genes. Phylogenies of the SSU and LSU rRNA genes were used to determine whether Togninia has more affinity with the Calosphaeriales or the Diaporthales . These results confirmed that Togninia had a higher affinity to the Diaporthales than the Calosphaeriales . Examination of type specimens revealed that T.cornicola , T.vasculosa , T . rhododendri, T . minima var. timidula and T.villosa , were not members of Togninia . New combinations such as Calosphaeria cornicola,Calosphaeriarhododendri , Calosphaeriatransversa , Calosphaeriatumidula,Calosphaeriavasculosa and Jattaeavillosawere therefore proposed to accommodate these species.

    The correct and rapid identification of Phaeoacremonium species is important tofacilitate the understanding of their involvementin plant as well as human disease. A rapid identification method was developed for the 22 species of Phaeoacremonium currently recognised. It involved the use of 23 species-specific primers, including 20 primers targeting the β-tubulin gene and three targeting the actin gene. These primers can be used in 14 multiplex reactions. Additionally a multiple-entry electronic key based on morphological, cultural andb-tubulin sequence data was developed to facilitate routine species identification. This database can be accessed online athttp://www.cbs.knaw.nl/phaeoacremonium.htm. With this identification tool phenotypic and sequence data can be used to identify the different Phaeoacremonium species. Separate dichotomous keys were provided for the identification of the Togninia and Phaeoacremonium species based on phenotypic characters. Additionally, keys for the identification of Phaeoacremonium -like fungi and the genera related to Togninia were also provided. 

    The mating strategy of several Togninia species was investigated with ascospores obtained from fertile perithecia produced in vitro . Togninia argentinensis and T.novae-zealandiae have homothallic mating systems, whereas T. austroafricana , T. krajdenii , T. minima , T.parasitica , T. rubrigena and T. viticola are heterothallic. The species predominantly isolated from diseased grapevines are Pm. aleophilum , Pm. parasiticum and Pm. viticola . Perithecia of two of these species, T. minima and T. viticola , have been found on grapevines in the field, indicating that these species recombine in vineyards. 

    The genetic diversity among isolates ofPa.chlamydospora on grapevines was investigated by means of Amplified Fragment Length Polymorphisms (AFLPs). Phaeomoniellachlamydospora isolates were collected from different positions on the same vine, different vines within a vineyard and different vineyards withinSouth Africa. Selected isolates from various grape producing countries, namelyAustralia,France,Italy,Iran,New Zealand,SloveniaandU.S.A.were also included. The overall low level of genetic variation confirmed asexual reproduction to be dominantin the field. Different genotypes were found among isolates ofPa.chlamydospora within the same grapevine, suggesting multiple infections from different inoculum sources. Isolates from different countries had a high percentage of similarity and clustered together, indicating the absence of genotype-geographic structure. The presence of the same genotype in different vineyards and production areas suggests that long-range dispersal through aerial inoculum or infected plant material played an important role in genotype distribution. 

    Seven species of Togninia and 15 species of Phaeoacremonium were newly described during the course of this study. The data obtained in this study, as well as the newly developed dichotomous and online polyphasic keys will enable scientists to correctly identify all the known species and also provide a reference database to which new species can be added in future. The newly reported host ranges and distributions, together with pathogenicity data, will enable scientists to identify species of possible quarantine concern.

    Valse meeldauw bij komkommer
    Gaag, D.J. van der - \ 2004
    vruchtgroenten - komkommerfamilie groenten - cucumis - komkommers - bestrijdingsmethoden - pseudoperonospora cubensis - rassen (planten) - deuteromycotina - klimaatregeling - glastuinbouw - fruit vegetables - cucurbit vegetables - cucumis - cucumbers - control methods - pseudoperonospora cubensis - varieties - deuteromycotina - air conditioning - greenhouse horticulture
    Valse meeldauw wordt veroorzaakt door de schimmel Pseudoperonospora cubensis. Deze schimmel dringt de bladeren binnen waarna hoekige vlekken ontstaan begrensd door de bladnerven. De vlekken zijn eerst licht chlorotisch, vervolgens geel en daarna bruin. Bij hoge luchtvochtigheid worden sporen gevormd aan de onderkant van het blad dat zichtbaar is als een paars pluis. De schimmel heeft levend plantmateriaal nodig om te groeien. Korte perioden zonder komkommerplanten kan de schimmel overleven via sporen die aan de onderkant van zieke bladeren worden gevormd (de “sporangia”)
    Biological control of Botrytis spp. by Ulocladium atrum : an ecological analysis
    Kessel, G. - \ 1999
    Agricultural University. Promotor(en): R. Rabbinge; J. Koehl; W. van der Werf. - S.l. : [s.n.] - ISBN 9789058081490 - 155
    botrytis cinerea - plantenziekteverwekkende schimmels - biologische bestrijding - deuteromycotina - mycelium - dematiaceae - botrytis cinerea - plant pathogenic fungi - biological control - deuteromycotina - mycelium - dematiaceae

    Plant pathogenic fungi from the genus Botrytis cause economically important diseases in a wide range of crops during the production phase as well as post harvest phase. Control is based on the frequent use of fungicides. Alternative approaches for control are studied because of the development of fungicide resistance in the pathogen and environmental concerns.

    The fungal saprophytic antagonist Ulocladium atrum is an effective biological control agent of B. cinerea in cyclamen. U. atrum may also be effective against B. cinerea in other crops and against other Botrytis spp. The biocontrol effect of U. atrum is based on a competitive interaction with B. cinerea in plant tissue. An immuno-histological technique was developed to visualize the interaction between the mycelia of Botrytis spp. and U. atrum in plant tissue and quantify colonization levels. Nutrient competition was found to be the dominant antagonistic mechanism between the species and pre-emptive colonization of plant tissue by U. atrum was identified as the most promising biocontrol strategy. Necrotic plant tissue is the primary target for U. atrum applications, since this is the (only) niche available to both Botrytis spp. and U. atrum .

    Pre-emptive colonization of naturally necrotic tissue by U. atrum was highly effective against B. cinerea in cyclamen, whereas U. atrum applications against B. elliptica in lily were ineffective. A comparison of both pathosystems suggests three criteria that govern the potential success of U. atrum as a biocontrol agent. 1) There must be a niche in which U. atrum competes with the pathogen; 2) The competitive ability of U. atrum in this niche has to be sufficient to allow for competitive exclusion of the pathogen. 3) The niche from which the pathogen can be excluded has to be essential for disease development. Colonies of U. atrum have lower radial growth rates than those of the Botrytis spp. studied. In practical biocontrol, this competitive disadvantage of the antagonist can be overcome by applying a high density of its conidia in a uniform distribution on the target tissue.

    Public health aspects of Fusarium mycotoxins in food in The Netherlands : a risk assessment
    Nijs, M. de - \ 1998
    Agricultural University. Promotor(en): F.M. Rombouts; S.H.W. Notermans. - S.l. : De Nijs - ISBN 9789054858072 - 140
    volksgezondheid - gezondheidszorg - mycotoxinen - aflatoxinen - deuteromycotina - nederland - tuberculariaceae - public health - health care - mycotoxins - aflatoxins - deuteromycotina - netherlands - tuberculariaceae

    Plant pathogenic Fusarium moulds occur world-wide and cereals can become infected during the growing period. Fusarium was detected in 83 % of 69 cereal samples of batches intended for food or feed production and harvested in The Netherlands in 1993. A considerable genotypic and phenotypic variation was observed within two of the most frequently isolated Fusarium species. Mycotoxins can be excreted in the crop by the fungus after the plant becomes infected. A literature review revealed 137 secondary metabolites that could be, produced by Fusarium species which were isolated from food raw materials. Twelve of those secondary metabolites were identified as mycotoxins based on toxicity observed in test animals. Six of those twelve have possibly been involved in human disease outbreaks (T-2 toxin, nivalenol, deoxynivalenol, acetyldeoxynivalenol, fumonisin B1 and zearalenone). Most of the mycotoxins are stable under process conditions used for food production and can be detected in food. Cereals harvested in The Netherlands in 1993 were contaminated with deoxynivalenol (food poisoning and immunotoxic), 3 %, or zearalenone (oestrogen), 1 %. Fumonisin B 1 (carcinogenic, related to human oesophageal cancer) was detected in 98 % of samples of maize from batches imported in The Netherlands and intended for food production. A 28-day toxicity study on the effects of fumonisin B 1 in rats revealed dose-response related apoptosis in the kidney. The lowest observed effect level was at 0.19 mg fumonisin B 1 kg -1rat body weight. The data on fumonisin B 1 toxicity were used to estimate a tolerable daily intake (TDI) of 500 ng fumonisin B 1 kg -1human body weight. The probability of being daily exposed to fumonisin B 1 at a level corresponding to this TDI was 12 % for the people in The Netherlands consuming the average amount of maize, 55 % for people belonging to the group of 'eaters only' and 78 % for people with gluten intolerance. The health of the consumers in The Netherlands might, in the current situation, be challenged by Fusarium mycotoxins present in food. Deoxynivalenol, which has immunotoxic characteristics, can potentially be present in food and feed and might increase human exposure to infectious diseases, especially to those from zoonotic origin.

    Rhizoctonia disease of tulip : characterization and dynamics of the pathogens
    Schneider, J.H.M. - \ 1998
    Agricultural University. Promotor(en): J.C. Zadoks; N.J. Fokkema. - S.l. : Schneider - ISBN 9789054858522 - 173
    plantenziekteverwekkende schimmels - deuteromycotina - bloembollen - plantenziektekunde - plantenfysiologie - tulipa - tulpen - rhizoctonia - plantenziekten - moniliaceae - tulipa - tulips - rhizoctonia - plant pathogenic fungi - deuteromycotina - ornamental bulbs - plant pathology - plant physiology - plant diseases - moniliaceae

    Rhizoctonia disease causes severe losses during the production cycle of tulip. The complex nature of the disease requires a precise characterization of the causal pathogens. Typical bare patches are caused by R. solani AG 2-t. Bulb rot symptoms are, apart from AG 2-t isolates, caused by R. solani AG 5. AG 4 isolates seem of little importance in field-grown tulips.

    Anastomosis behaviour showed AG 2-t to be a homogeneous group, closely related to the heterogeneous group of AG 2-1 isolates. Pectic enzyme patterns discriminated tulip infecting AG 2-t isolates from AG 2 isolates not pathogenic to tulip. Geographically separated AG 2-t and AG 2-1 isolates, both pathogenic to tulip, differ in nucleotide number and sequence of ITS rDNA.

    Differential interaction between AG 2-t isolates and tulip cultivars was highly influenced by experimental conditions. According to geostatistical analysis field sampling intensity could be reduced down to 10% and still provided adequate disease severity maps. Bare patches due to natural and artificial infestation declined during successive croppings of bulbs, whereas bulb rot tended to increase. Temporal niche differentiation is one explanation for the decline phenomenon.

    The AVR9 elicitor peptide of the tomato pathogen Cladosporium fulvum : molecular aspects of recognition
    Kooman - Gersmann, M. - \ 1998
    Agricultural University. Promotor(en): P.J.G.M. de Wit; G.J.E.M. Honee. - S.l. : Kooman-Gersmann - ISBN 9789054857938 - 117
    tomaten - passalora fulva - deuteromycotina - solanum lycopersicum - fysiologie - gastheer parasiet relaties - moleculaire biologie - plantenziektekunde - ziekteresistentie - genen - genomen - dematiaceae - tomatoes - passalora fulva - deuteromycotina - solanum lycopersicum - physiology - host parasite relationships - molecular biology - plant pathology - disease resistance - genes - genomes - dematiaceae

    The interaction between the fungal pathogen Cladosporium fulvum and tomato has been used as a model system to study the molecular basis of gene-for-gene relationships. C. fulvum is a specialized, biotrophic pathogen, which causes leaf mold on tomato. Under humid conditions conidia of C. fulvum germinate and form runner hyphae on the lower side of the leaf. If no resistance genes of the plant match any of the avirulence genes of the fungus, the interaction is compatible and infection will proceed. However, when both a resistance gene and its matching avirulence gene are present, the plant recognizes the fungus and the interaction is incompatible. In an incompatible interaction active defense responses, including the hypersensitive response (HR) are initiated, which inhibit fungal growth effectively. Avirulence genes encode lace-specific elicitors, which are present in intercellular washing fluids obtained from compatible interactions of C. fulvum and tomato (De Wit and Spikman, 1982). Injection of these intercellular washing fluids in tomato plants resistant to the C. fulvum strain from which the washing fluids were obtained, results in specific necrosis at the site of injection. The race-specific elicitor AVR9 was isolated and purified (Scholtens-Toma and de Wit, 1988). AVR9 specifically induces necrosis on tomato genotypes carrying the Cf-9 resistance gene. The encoding AVR9 gene was isolated, and it was shown that this gene specifically determines avirulence of C. fulvum on tomato plants carrying the Cf-9 resistance gene (Van den Ackerveken et al., 1992; Marmeisse et al., 1993). The Avr9 gene encodes a 63-amino acid pre-proprotein containing one potential glycosylation site (Van den Ackerveken et al., 1993). Different forms of the AVR9 elicitor were found, of which the mature AVR9 elicitor of 28 amino acids is predominantly present in C. fulvum-infected tomato plants (Van den Ackerveken et al., 1993). The global structure of the AVR9 peptide shows 3 antiparallel β-sheets and 3 disulfide bonds that are arranged in a cystine knot (Vervoort et al., 1997).

    In the research project described in this thesis, we studied AVR9 elicitor perception in tomato plants that carry the Cf-9 resistance gene and compared the results to those obtained with tomato plants lacking this gene. Previously, several research groups had shown that elicitors are recognized through plants receptors, which are localized on the plasma membrane (summarized in chapter 1). To find and characterize the receptor for AVR9, the peptide was labeled with iodine-125 and binding to tomato membranes was studied, as presented in chapter 2. 125 I-AVR9 showed specific, saturable, and reversible
    binding to plasma membranes isolated from leaves of the tomato cultivar Moneymaker without Cf resistance genes (MM-Cf0) and to membranes from a near-isogenic genotype containing the Cf-9 resistance gene (MM-Cf9). Binding of AVR9 is characterized by high affinity and low receptor concentration, and thus fulfills several criteria expected for functional receptors (Hulme and Birdsall, 1992). The dissociation constant was determined at 0.07 nM, and the receptor concentration was determined at 0.8 pmol/mg microsomal membrane protein. Binding is highly influenced by pH and ionic strength of the binding buffer and by temperature, indicating the involvement of both electrostatic and hydrophobic interactions. Surprisingly, binding kinetics and binding capacity were identical for membranes of the MM-Cf0 and MM-Cf9 tomato genotype, indicating that the Cf-9 resistance gene is not required for binding of AVR9. By that time, the Cf-9 resistance gene was isolated (Jones et al., 1994). Cf-9 belongs to a gene family and homologues of the Cf-9 resistance gene are present in both resistant and susceptible tomato genotypes. Two new hypotheses were developed of which the first predicts that not only the Cf-9 resistance gene, but also homologues of the Cf-9 gene, encode the high-affinity binding site for AVR9. Only the protein encoded by Cf-9 itself, designated CF-9, would subsequently initiate the signal transduction cascade resulting in HR. The second hypothesis predicts that the AVR9 binding site is neither CF- 9 nor a homologue of CF-9. The binding site proposed in the second hypothesis would bind AVR9 and subsequently recruit the CF-9 protein to initiate HR.

    As described in chapters 3, 4, and 5, experiments were performed to prove or reject one of these two hypotheses. To determine whether the high-affinity binding site for AVR9 is indeed a functional receptor, we studied the correlation between binding affinity and necrosis-inducing activity of mutant AVR9 peptides. We determined structure-activity relationships of the AVR9 peptide by independently substituting each amino acid of AVR9 by alanine, using a site-directed mutagenesis approach. In addition, surfaceexposed amino acid residues of AVR9 were substituted by other amino acids. Activity of mutant Avr9 constructs was studied by expressing the constructs in MM-Cf9 tomato plants using the potato virus X (PVX) expression system, and assessing the severity of necrosis induced by each PVX::Avr9 construct. This allowed direct identification of amino acid residues of AVR9 that are essential for elicitor activity. We identified amino acid substitutions resulting in AVR9 mutants with higher, similar or lower elicitor activity compared to the wild-type AVR9 peptide. Mutants of the amino acid residues Phe21 and Leu24 had completely lost elicitor activity. Necrosis-inducing activity of isolated AVR9 peptides correlated well with the necrosis induced by the corresponding PVX::Avr9 constructs. It was concluded the PVX expression system is ideally suited to analyze necrosis-inducing activity of AVR9 peptides. We analyzed whether there is a correlation between elicitor activity of the mutant AVR9 peptides and their affinity to the binding site in membranes of tomato. Therefore, Nicotiana clevelandii plants were inoculated with a selection of PVX::Avr9 constructs and mutant AVR9 peptides were purified from these plants. In addition, some AVR9 peptides were chemically synthesized. Characterization by Electrospray Mass Spectrometry, Circular Dichroism-, and 'H-NMR- spectroscopy revealed that both the in planta produced and the synthetic mutant peptides were correctly folded. AVR9 peptides purified from PVX::Avr9-infected N. clevelandii contained one N-acetylglucosamine, although small amounts of non- glycosylated AVR9 peptides were also detected. The glycosylated AVR9 peptides showed lower affinity to the binding site than the non-glycosylated AVR9 peptides, whereas they did not differ significantly in necrosis-inducing activity. For both the non- glycosylated and glycosylated mutant AVR9 peptides, a positive correlation between their affinity to the membranelocalized binding site and their necrosis-inducing activity in MM-Cf9 tomato was found, i.e. peptides with higher affinity to the binding site showed higher necrosis-inducing activity. This correlation suggested that the characterized high-affinity binding site for AVR9 is indeed a functional receptor that initiates the AVR9- CF-9-dependent HR in MM-Cf9 plants.

    In chapter 5, we studied whether the Cf-9 resistance gene or (one of) its homologues code for an AVR9 binding site. We tested binding of AVR9 to microsomal membranes of a variety of solanaceous and non-solanaceous plant species and analyzed these species for the presence of Cf-9-homologues. All solanaceous species tested contain homologues of the Cf-9 resistance gene and membranes of these plants contain a highaffinity binding site for AVR9. However, a high affinity binding site for AVR9 is also present on membranes of the non-solanaceous plant species cucumber, barley and oat, which do not contain homologues of the Cf-9 resistance gene. Membranes of tobacco, transgenic for the Cf-9 resistance gene, showed no change in the number of AVR9 binding sites. Arabidopsis does not have a binding site for AVR9 and membranes of Arabidopsis, transgenic: for the Cf-9 resistance gene, also showed no AVR9 binding. From this we concluded that not only the Cf-9 resistance gene, but also its homologues are not required for high-affinity binding of AVR9. Based on the presented data, we have developed a model, explaining recognition of AVR9 in MM-Cf-9 tomato (chapter 6). This model predicts that the high-affinity binding protein either 'presents' the AVR9 elicitor to the Cf-9-encoded protein or that binding of AVR9 induces a conformational change of the high-affinity binding protein. The latter results in recruitment of Cf-9 into the AVR9- receptor complex. Subsequently, signal cascade(s) resulting in HR will be initiated.

    On ecology and control of Mycocentrospora acerina in caraway (Carum carvi)
    Evenhuis, A. - \ 1998
    Agricultural University. Promotor(en): J.C. Zadoks. - S.l. : Evenhuis - ISBN 9789054858515 - 193
    plantenziekteverwekkende schimmels - deuteromycotina - carum carvi - karwij - gewasbescherming - plagenbestrijding - ziektebestrijding - mycocentrospora acerina - plant pathogenic fungi - deuteromycotina - carum carvi - caraway - plant protection - pest control - disease control - mycocentrospora acerina

    This thesis describes aspects of the biology of Mycocentrospora acerina (Hart.) Deighton and their implications for caraway ( Carum carvi L.) cultivation. The biology of M. acerina under field conditions was not yet described satisfactorily. More is known of M. acerina as the causal agent of liquorice rot, a post-harvest disease in carrots. Various studies in caraway were performed in the period from 1990 until 1995 with the aim to obtain information on M. acerina and to generate a set of crop protection methods based on this information. Chapter 1 provides an introductory overview.

    Chapter 2 reports on the dispersal of conidia of M. acerina in caraway field trials. A Burkard spore trap, rotorods, inverted Petri dishes containing sucrose agar and rain gauges were used to trap conidia of M.acerina . Sporulation was stimulated by rainfall (≥2 mm) and moderate temperatures (around 15°C). Solar radiation had a negative effect on sporulation. Hardly any conidia were found in the spore traps on rainless days. Short distance (≤9 m) spread of M.acerina was mainly caused by splash dispersal of its conidia. Trap plants at 0 to 4 m from the inoculum source were readily infected under moist conditions. Beyond 9 m from an inoculum source no infection of caraway trap plants was found. Trap plants at 9 m from an inoculum source were infected in one out of three seasons only. Long distance (> 9 m) spread could not be demonstrated by the techniques used in this study. The results suggest that, usually, a caraway field is infected by inoculum sources within that field.

    Chapter 3 deals with the effect of mechanical injury on disease incidence, incubation period and lesion development rate on caraway roots following infection by M. acerina . After inoculation with M. acerina , disease incidence of injured roots was significantly higher than of non-injured roots under laboratory conditions. The incubation period of M. acerina was significantly shorter on injured roots than on non-injured roots. The incubation period shortened with increasing root injury level. Younger injured roots tended to be more resistant to M. acerina infection than older injured roots, as expressed by longer incubation periods. The lesion development rate was, on average, higher on heavily injured roots than on non-injured or slightly injured roots. The lesion development rate remained fairly constant after the first appearance of the symptoms on the caraway root, until the whole root was colonized. Caraway roots carefully dug up in autumn frequently showed injuries enabling M. acerina to penetrate the roots. However, the correlation between root injury and root rot after cold storage was weak. Injury of roots had a stimulating effect on infection by and development of M. acerina , but roots without wounds could be infected too.

    Seed transmission of M. acerina in caraway is demonstrated in Chapter 4. Seed transmission efficiency varied between 27 and 62%. Methods to quantify M. acerina seed infection in caraway are presented and discussed. Seed infection levels were usually less than 3%, but infection levels up to 50% were found. M. acerina remained viable in caraway seeds for at least three years. Results suggest that infected caraway seed can be an inoculum source for the development of anthracnose in caraway crops. The importance of seed infection for long distance dissemination and for the onset of an epidemic is discussed.

    The effect of seed infection of caraway by M. acerina on crop establishment and yield was studied in field experiments described in Chapter 5. High seed infection levels hampered crop establishment of caraway and limited the number of plants producing a root diameter large enough to permit flowering in the next year.

    Chapter 6 reports on the search for inoculum sources of M. acerina on caraway. Obvious suspects are cover crops of biennial caraway and preceding crops of annual caraway. Other suspects are weeds in or alongside the field. Finally, survival structures of the fungus, chlamydospore chains, packed in plant debris or naked, are suspected. M. acerina is able to infect many plant species, including cover crops of caraway such as spinach for seed production and peas. However, the agronomical suitability of a crop to serve as a cover crop of biennial caraway proved to be a more important factor in determining caraway yield than the susceptibility of the cover crop to M. acerina . This finding was corroborated by the fact that spinach and peas as preceding crops had no significant effects on M. acerina development in spring caraway sown the next year. Dill, barley and four weed species were found as new hosts of M. acerina . The role of weed hosts, susceptible crops and plant debris in the survival of the fungus in years without caraway is discussed. Caraway sown on soil containing infested caraway straw, infested debris of other plant species or chlamydospores grown in pure culture, became infected by M. acerina . Only high inoculum densities of chlamydospores in the soil caused severe damping-off of caraway seedlings. The opportunity for disease management by agronomical means is quite limited.

    Chapter 7 describes the effect of some cultivation measures on anthracnose development in caraway. A reduction of leaf wetness duration was positively correlated with a decrease of disease severity. Lodging and higher plant density prolonged leaf wetness duration. Disease incidence and severity of anthracnose were reduced by crop management activities minimizing leaf wetness duration. Reduction of nitrogen levels reduced the risk of anthracnose development in spring and biennial caraway. Decreasing the sowing rate from 8 to 4 kg ha -1resulted in a lower disease severity and an increase of seed yield in spring caraway, but not in biennial caraway. In biennial caraway disease severity decreased with wider row spacing. A damage threshold between 6% and 12% disease severity is proposed. Positive financial results of crop management activities are indicated.

    Relationships between scientific aspects described in the previous chapters and the applied research described elsewhere are discussed in Chapter 8. Problems with anthracnose of caraway occur after long periods of rainfall. The disease cannot be prevented by any single crop protection measure. However, some measures reduce the occurrence of M. acerina. Reducing the risk of yield loss due to this pathogen should begin with 1) a disease-free start to delay the build-up of inoculum (disease-free seeds, choice of an uncontaminated field), 2) slowing down the epidemic in spring by taking measures to avoid lodging and to limit leaf wetness duration in a crop (reduction of sowing rate, intermediate row spacing and reduction of nitrogen fertilization), and 3) seed dressing can retard the early infection of seedlings, but it is illegal in the Netherlands. Fungicides against white mould ( Sclerotinia sclerotiorum ) sometimes reduce anthracnose in caraway, but results cannot be guaranteed.

    Fusarium head blight resistance in wheat : using the in vitro androgenic approach
    Bruins, M.B.M. - \ 1998
    Agricultural University. Promotor(en): E. Jacobsen; C.H.A. Snijders. - S.l. : Bruins - ISBN 9789054858638 - 130
    plantenveredeling - ziekteresistentie - plaagresistentie - plantenziekteverwekkende schimmels - deuteromycotina - triticum aestivum - tarwe - hexaploïdie - tuberculariaceae - plant breeding - disease resistance - pest resistance - plant pathogenic fungi - deuteromycotina - triticum aestivum - wheat - hexaploidy - tuberculariaceae

    Wheat ( Triticum aestivum L.) belongs to the three most important food crops in the world. In certain years, the crop can suffer considerable damage as a result of Fusarium Head Blight (FHB), especially as no chemical control is effective against this disease. This disease is mainly caused by the fungi Fusarium culmorum and F. graminearum but in the cooler regions of North-Western Europe, F. culmorum predominates. The pathogen causes a wide range of different damage, of which toxin contamination of the seeds is among the most threatening. These toxins, of which deoxynivalenol (DON), nivalenol (NIV) and acetyldeoxynivalenol (ADON), with the isomers 3-ADON and 15-ADON are most notorious, are capable of inhibiting protein synthesis and are, therefore, extremely hazardous to man and animal. For economic and environmental reasons, host plant resistance is the most appropriate and sustainable disease control method and should be given a high priority in any wheat breeding programme.

    Androgenesis is the outgrowth of the male reproductive cell into a haploid plant. Up until now, for more than 250 plant species haploid plants have been produced via in vitro androgenesis. However, when using the in vitro androgenesis technique there are still specific problems to be solved for the individual crops. The applications and advantages of in vitro androgenesis are for example rapid production of haploid plants evoking a shorter breeding regime, easier genetic analyses both at crossings and at the DNA level and possibilities for genetic modification and in vitro selection. In vitro selection has been used efficiently to find agronomically altered traits and to produce new cultivars. With the use of toxins as selective agent new resistances have been found in wheat, e.g. against Pseudomonas syringae pv. syringae or Helminthosporium sativum . A general overview on Fusarium Head Blight (FHB), on toxicity of the toxins produced by this pathogen, on in vitro androgenesis and in vitro selection is presented in Chapter 1.

    In Chapter 2, the results of a 7x7 full diallel on the inheritance of androgenic ability in wheat anther culture are presented. Seven parental cultivars, differing in both androgenic response and FHB-resistance, together with the 42 F 1 -combinations of the complete diallel were evaluated for several androgenic traits in five replicates. In total 130,000 anthers were cultured, of which 14% responded. Diallel data were analysed by the model of Gardner and Eberhart and it appeared that most of the genetic variation could be explained by additive genetic effects. A total of 17,819 embryos were transferred to MS regeneration medium, of which on average 30% regenerated into plantlets. Of them 11% was green. Except for two combinations, green plants were recovered from all 42 F 1 -combinations. Significant genetic differences were found and genetic effects explained 38%, 48% and 21% of the total variation for the percentage of green regenerants, the percentage of albino regenerants and the percentage of embryos that formed only roots, respectively. Additive effects explained 30%, 65% and 37% of the genetic variation and narrow sense heritabilities were 0.11, 0.32 and 0.08, respectively. Replicate effects were highly significant for the factors percentage albino regenerants and percentage embryos with only root formation. No significant General Combining Ability (GCA) effects were found. Variety heterosis was only significant for the percentage green regenerants and specific heterosis was significant for percentage green- and percentage albino regenerants. No reciprocal effects were found. Large significant differences in Specific Combining Ability (SCA) values were observed, with 13.5% of the F 1 -combinations outyielding the best parent.

    About 2,000 plants were doubled with colchicine and 84% of the doubled haploid (DH) plants could be grown to seed set. For seed set, genetic effects explained 78% of the total variation, but additive effects where responsible for only 4% of the genetic variation and, therefore, the narrow sense heritability was low (0.01). According to heritabilities, for embryo production progress can be rapid, for green plant regeneration it will be important to choose the parents very carefully and for seed set, progress is more hard to make. No correlation between embryo production, plant regeneration or seed set could be found. Over 200,000 seeds were formed on the DH-genotypes.

    A low green plant regeneration is considered to be one of the main bottlenecks for efficient use of the in vitro androgenesis technique in wheat. To study the inheritance of anther culture response and green plant regeneration more specifically, reciprocal crosses were made between the wheat cultivars Ringo Sztar, Ciano 067 and Benoist H77022, each of which had both a good response in anther culture and a high frequency of green plant regeneration (Chapter 3). It was found that, averaged for all genotypes, 23.0% of the anthers responded and a callus induction frequency of 77.8% was observed.

    Furthermore it appeared that of all the embryos, 43.0% developed into plantlets, 25.6% of the regenerants being green, resulting in 3.3 green plants per 100 anthers. It was also found that genotypic effects accounted for 57.7%, 86.3% and 77.5% of the total variance of anther culture response, callus induction frequency and embryo induction frequency, respectively. Additive and dominant gene actions were detected for all androgenesis and regeneration characteristics and no reciprocal differences were found, indicating the absence of cytoplasmic effects. It was concluded that embryo production was primarily correlated with anther culture response and not with the number of embryos produced per plated anther or per responding anther.

    Advantages of in vitro selection compared to in vivo selection are that a larger number of genotypes can be screened under controlled conditions and that a limited amount of space is needed to screen all genotypes. For wheat, resistance against several diseases was reported through in vitro selection with the help of toxins as selective agent. In order to elucidate the phytotoxicity of FHB-produced toxins, effects were studied on four types of wheat plant material i.e. seedlings, coleoptile segments, anther derived callus and anther derived embryos, using different concentrations of DON and 3-ADON (Chapter 4). It appeared that DON inhibited growth of all types of plant material and that the seedling growth response to 4´10 -5M DON of a large set of genotypes did not differentiate between tolerant and sensitive genotypes according to the observed FHB-resistance level in the field. In general, coleoptile segments showed a growth reduction at 10 -5M DON, whereas a concentration of 10 -4M DON appeared to be the optimum concentration to differentiate between haploid wheat calli for DON-tolerance. However, growth analysis data of 40 callus clones did not show any correlation with the known FHB-resistance levels of the original donor genotypes and populations. Regeneration of the anther derived embryos in the embryo selection experiment was decreased 100-fold on DON-containing medium. Averaged across the callus and embryo selection experiments, green plant regeneration showed a decrease of approximately 20-fold on medium containing the toxin.

    Most of the resistance genes against FHB that are known up to now, are located in for European standards considered exotic wheat genotypes and introduction of these genes into varieties requires extensive backcrossing. A haploid step could accelerate the transfer of the genes to cultivars. The final aim of our research was selection for high FHB-resistance in the field and, therefore, crosses were made between resistant and susceptible genotypes for four consecutive years (Chapter 5). Parents, F 1 - or F 2 -populations were used as donor material for anther culture and were, together with the anther culture derived doubled haploid (DH) wheat lines, tested in the field for their FHB-resistance. Percentage infection was measured three and four weeks after artificial inoculation.

    Besides infection, also date of flowering and, during two years, straw length was scored. The observed plant traits within the various DH-lines were stable, homogeneous and no visible segregation occurred. In most cases, the F 1 -, F 2 -populations and the DH-lines were for infection level intermediate between the two parental infection levels, indicating an additive inheritance. However, the infection levels of some of the doubled haploids were significantly lower than the levels of the most resistant parent. In cases where the F 2 -populations were significantly more resistant than the two parents, it was concluded that accumulation of resistance genes of the partially resistant parents had occurred. In cases where the DH-lines, derived from cultivars were significantly more resistant than the cultivars, it was attributed to gametoclonal variation. No evidence was found that a longer callus phase might lead to a higher level of variation. In 1994 infection levels were substantially higher than in the three previous years, probably due to higher maximum temperatures in the inoculation period.

    Microspore culture has several advantages over anther culture, e.g. for in vitro selection experiments, single cells are preferred to multicellular structures as a more uniform selection pressure is secured. The possibility of using isolated microspore culture of wheat for in vitro selection experiments are described in Chapter 6. Experiments were carried out to optimise the isolation and culture of isolated microspores of this recalcitrant crop. It was found that the viability of the microspores was better when co-cultured with wheat ovaries from one cultivar as compared to co-culture with a mixture of wheat ovaries from four cultivars. Furthermore it appeared that co-culture of the microspores with ovaries in culture plate inserts had no significant effect on viability of the microspores, but had, in comparison with culture in agarose rings, a large positive effect on the percentage of swollen microspores. A significant correlation between the number of swollen microspores and the number of multicellular structures was found.

    For future research it will be necessary to analyse the progenies of the diallel-derived DH-regenerants for their FHB-resistance for several generations. It has to be elucidated whether or not the resistance levels of the highly resistant DH-genotypes will also be found in their offspring. Because in some DH-lines accumulation of resistance genes appears to have occurred, these lines will be very useful in breeding for introgression of this trait into commercial varieties.

    Wheat and maize, two of the three most important food crops in the world, are affected by Fusarium head blight. Research on FHB resistance and resistant cultivars are of the utmost importance to ensure an adequate food supply around the world.

    Early decline of asparagus in the Netherlands : etiology, epidemiology and management
    Blok, W.J. - \ 1997
    Agricultural University. Promotor(en): M.J. Jeger; G.J. Bollen. - S.l. : Blok - ISBN 9789054857778 - 177
    asparagus - deuteromycotina - plantenplagen - plantenziekten - epidemiologie - distributie - bestrijdingsmethoden - geïntegreerde plagenbestrijding - geïntegreerde bestrijding - fusarium oxysporum - tuberculariaceae - asparagus - deuteromycotina - plant pests - plant diseases - epidemiology - distribution - control methods - integrated pest management - integrated control - fusarium oxysporum - tuberculariaceae

    Asparagus plants on fields cropped with asparagus before establish well but economic life of the crop is only half of that on fresh land. Fusarium oxysporum f.sp. asparagi was identified as the main cause of this early decline. Autotoxic compounds were detected in residues of asparagus roots even 11 years after the crop was finished but evidence for a role of these compounds in the etiology of the disease was not obtained. The pathogen was found on asparagus seed, on one-year-old crowns used as planting material and was isolated from soil, frequently even from fields without an asparagus history. In inoculation experiments, the pathogen caused severe root rot in asparagus, mild root rot occasionally in pea and lupin, and it colonized the roots of many plant species that did not show symptoms. Twenty-four isolates of the pathogen were assigned to 18 vegetative compatibility groups indicating the large genetical diversity of the population in the Netherlands. The potential of nonpathogenic isolates of F. oxysporum to reduce severity of Fusarium root rot was shown in growth chamber and greenhouse tests but not when plants were grown in the field for one year. A new method for reducing soil infestation with Fusarium oxysporum f.sp. asparagi and other soilborne pathogens was developed. It is based on induction of fermentative soil conditions. When fresh broccoli or grass was incorporated into soil that was subsequently irrigated and covered with plastic mulch, oxygen in soil was rapidly depleted and redox potential (Eh) reached values as low as -200 mV. After 15 weeks, populations of F. oxysporum f.sp. asparagi , Rhizoctonia solani , Verticillium dahliae , and Globodera pallida were strongly reduced in inoculum samples buried in soil demonstrating the potential of this approach to control a range of soilborne pathogens.
    Rhizoctonia solani in tulp en iris : eindverslag van het project 'Rhizoctonia solani in tulp en iris in relatie tot de bodemreceptiviteit'
    Schneider, J.H.M. ; Dijst, G. ; Schilder, M.T. - \ 1996
    Wageningen : IPO-DLO (Urgentieprogramma bollenziekte- en veredelingsonderzoek ) - 26
    deuteromycotina - nederland - bloembollen - plantenziekteverwekkende schimmels - tulipa - iris - moniliaceae - deuteromycotina - netherlands - ornamental bulbs - plant pathogenic fungi - tulipa - iris - moniliaceae
    Afweermechanismen bij lelie tegen aantasting door Fusarium oxysporum : eindverslag van het project 'Afweermechanismen in lelie en gladiool tegen aantasting door Fusarium oxysporum'
    Baayen, R.P. ; Foerch, M.G. ; Dreven, F. van - \ 1996
    Wageningen : IPO-DLO (Urgentieprogramma bollenziekte- en veredelingsonderzoek ) - 33
    deuteromycotina - ziekteresistentie - nederland - bloembollen - plaagresistentie - plantenziekteverwekkende schimmels - planten - lilium - tuberculariaceae - deuteromycotina - disease resistance - netherlands - ornamental bulbs - pest resistance - plant pathogenic fungi - plants - lilium - tuberculariaceae
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