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.

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Ilyonectria palmarum sp. nov. causing dry basal stem rot of Arecaceae
Aiello, D. ; Guarnaccia, V. ; Vitale, A. ; Cirvilleri, G. ; Granata, G. ; Epifani, F. ; Perrone, G. ; Polizzi, G. ; Groenewald, J.Z. ; Crous, P.W. - \ 2014
European Journal of Plant Pathology 138 (2014)2. - ISSN 0929-1873 - p. 347 - 359.
black foot disease - 1st report - root-rot - cylindrocarpon-macrodidymum - phylogenetic trees - multigene analysis - united-states - trunk rot - grapevine - phytophthora
During surveys conducted in 2010–2013, a complete breakage or bending of the trunk and a dry basal stem rot were observed on containerised Brahea armata, B. edulis, Howea forsteriana and Trachycarpus princeps plants in different nurseries located in eastern Sicily (southern Italy). A cylindrocarpon-like species was consistently obtained from diseased palm tissues, while known pathogens of these hosts such as Ganoderma, Phytophthora and Thielaviopsis were not found associated with symptomatic tissues or isolated on standard or selective media. A total of 40 cylindrocarpon-like isolates were collected and characterised based on morphology and DNA phylogeny. Multigene analyses based on the ß-tubulin, histone H3, translation elongation factor 1-a, and the internal transcribed spacers (ITS1, 5.8S, ITS2) genes facilitated the identification of a new species, described here as Ilyonectria palmarum. The pathogenicity of one representative isolate collected from each palm species was tested on plants cultivated under nursery conditions and in a growth chamber. All isolates were pathogenic to B. armata, B. edulis, H. forsteriana, and T. princeps and symptoms identical to that observed in nurseries were reproduced. Dry basal stem rot and stem bending caused by Ilyonectria palmarum represents a potentially serious problem for nurseries cultivating containerised palms
Calonectria diseases on ornamental plants in Europe and the Mediterranean Basion: an overview
Vitale, A. ; Crous, P.W. ; Lombard, L. ; Polizzi, G. - \ 2013
Journal of plant pathology - Formerly Rivista di patologia vegetale 95 (2013)3. - ISSN 1125-4653 - p. 463 - 476.
cylindrocladium-crotalariae microsclerotia - forest tree nurseries - 1st report - root-rot - leaf-spot - crown rot - feijoa-sellowiana - soil-temperature - mastic tree - damping-off
Species of Calonectria and their cylindrocladium-like asexual morphs are important plant pathogens of agronomic and forestry crops, especially in the tropical and subtropical regions of the world. Calonectria species have been associated with a wide range of disease symptoms on a large number of plant hosts. On horticultural crops, most records of Calonectria species come from the Northern Hemisphere, where they occur mainly in gardens and ornamental nurseries. In Europe and the Mediterranean basin, several species are widespread in nurseries and cause extensive damage to ornamental plants. In the past, identification of species was based on phenotypic characters and sexual compatibility using standardised media. More recently, morphological characteristics, phylogenetic studies (DNA sequence data of the ß-tubulin, histone H3 and translation elongation factor-1a gene regions) and mating studies have revealed the presence of several cryptic species complexes that were formerly treated as single Calonectria species. These studies resulted in the introduction of several new species. Other studies aimed at understanding environmental sustainability focused attention on soil solarisation and biological control as means for controlling these pathogens. The potential use of biological control agents (BCAs) and chemicals for controlling Calonectria-induced diseases has recently been addressed. In this review we discuss the Calonectria species detected in Europe and the Mediterranean basin, and the disease management strategies. In view of the mandatory implementation of integrated pest management (IPM) for all European countries by 2014, this paper provides basic information as a platform for the adaptation of more sustainable integrated measures to control Calonectria diseases in European nurseries.
Genome-wide identification of Phytophthora sojae SNARE genes and functional characterization of the conserved SNARE PsYKT6
Zhao, W. ; Dong, S. ; Ye, W. ; Hua, C. ; Meijer, H.J.G. ; Dou, X. ; Govers, F. ; Wang, Y. - \ 2011
Fungal Genetics and Biology 48 (2011)3. - ISSN 1087-1845 - p. 241 - 251.
pathogen phytophthora - systematic analysis - root-rot - fusion - proteins - infestans - complex - localization - eukaryotes - mechanisms
Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) are central components of the machinery mediating membrane fusion and key factors for vesicular trafficking in all eukaryotic cells. Taking advantage of the available whole genome sequence of the oomycete plant pathogen Phytophthora sojae, 35 genes encoding putative SNARE proteins were identified in the genome of this organism. PsYKT6, one of the most conserved SNARE proteins, was functionally characterized by homology-dependent gene silencing. The phenotype analysis showed that PsYKT6 is important for proper asexual development, sexual reproduction, and pathogenesis on host soybean cultivars.
Effects of compost amendment and the biocontrol agent Clonostachys rosea on the development of charcoal rot (Macrophomina phaseolina) on cowpea
Ndiaye, M. ; Termorshuizen, A.J. ; Bruggen, A.H.C. van - \ 2010
Journal of plant pathology - Formerly Rivista di patologia vegetale 92 (2010)1. - ISSN 1125-4653 - p. 173 - 180.
soil microbial communities - organic amendments - biological-control - root-rot - sclerotia - survival - solarization - suppression - management - pathogens
Macrophomina phaseolina is a destructive pathogen causing charcoal rot of cowpea and other crops in the semi- arid areas of the Sahel (north-west Africa). Chemical management is not feasible in conditions of subsistence farming, and the plurivorous nature of the fungus limits the effectiveness of some cultural methods. This study aimed at identifying the effects of composting on the survival of M. phaseolina and of soil application of compost alone or in combination with the biocontrol agent Clonostachys rosea on inoculum density of M. phaseolina and on cowpea production. Inside the compost heap with diseased cowpea residues, the temperature reached 52 to 60°C and completely destroyed M. phaseolina microsclerotia. Addition of compost to planting holes significantly suppressed charcoal rot disease. Among the doses tested 6 tonnes of compost alone or supplemented with 50 kg NPK ha-1 resulted in 28-45% lower Area-Under- the-Disease-Progress-Curves (AUDPC) and 43-66% higher cowpea production. The addition of compost combined with C. rosea in the planting holes reduced the AUDPC up to 4-fold and increased the grain yield 2-5- fold. The best treatment was a mixture of two C. rosea isolates and the compost.
Daily changes of infections by Pythium ultimum after a nutrient impulse in organic versus conventional soils
He, M. ; Ma, W. ; Tian, G. ; Blok, W.J. ; Khodzaeva, A. ; Zelenev, V.V. ; Semenov, A.M. ; Bruggen, A.H.C. van - \ 2010
Phytopathology 100 (2010)6. - ISSN 0031-949X - p. 593 - 600.
damping-off - bacterial-populations - root-rot - pseudomonas-fluorescens - biological indicators - microbial communities - disease suppression - plant-pathogens - wheat roots - compost
Bacterial populations (CFU) have been shown to oscillate in wavelike patterns after nutrient impulses in previous studies. The amplitudes and periods of oscillations could possibly be used as indicators of soil health analogous to the stability and resilience of biological populations widely accepted as indicators for ecosystem health. Limited plant and animal disease outbreaks can also be viewed as a manifestation of a healthy soil ecosystem. Two pot experiments were carried out to verify whether damping-off of beet seedlings by Pythium ultimum, measured as area under the disease progress curve (AUDPC), fluctuated over time after incorporation of organic materials into organic versus conventional soils, and to investigate whether daily dynamics of AUDPCs were linked to the dynamics of microbial populations and chemical parameters. AUDPCs oscillated significantly over time when Pythium bioassays were initiated daily after addition of ground grass and clover shoots (GC) into unplanted soils. Similar oscillations with significant harmonics of AUDPC were also observed in composted manure (CM)-amended soils but with smaller amplitudes than in GC-amended soils. The AUDPC harmonics in amended soils had periods similar to those of CFU of copiotrophic bacteria. Cross-correlation analysis demonstrated that periodic fluctuations of P. ultimum infections (AUDPCs) did not coincide with those of copiotrophic CFU but were shifted in phase. It appears that competition or antagonism from some fast-growing bacteria influenced pathogen infections, because these bacterial populations were growing and dying. Soil chemical variables, including pH, dissolved organic carbon, and NO(3)(-)-N, and NH(4)(+)-N contents, changed significantly in the initial 7 days after a nutrient impulse into soils. These changes were cross-correlated with copiotrophic CFU with time lags of approximately 1 to 2 days but were seldom associated with daily changes in AUDPCs. Organically managed soils always had lower AUDPC ratios of amended to nonamended treatments, indicating that organic materials showed stronger suppressive abilities to P. ultimum in organic than in conventional soils. The oscillations in AUDPCs and copiotrophic CFU in amended organic soil also had smaller amplitudes than in amended conventional soil. These results suggested that organically managed soils had a greater resistance and resilience to the disturbance of the amendments and, therefore, could be considered healthier than conventionally managed soils
Species concepts in Calonectria (Cylindrocladium)
Lombard, L. ; Crous, P.W. ; Wingfield, B.D. ; Wingfield, M.J. - \ 2010
Studies in Mycology 66 (2010)1. - ISSN 0166-0616 - p. 1 - 13.
spathiphylli sp-nov - root-rot - 1st record - crown rot - collar rot - beta-tubulin - leaf-spot - microsatellite loci - female fertility - genome sequence
Species of Calonectria and their Cylindrocladium anamorphs are important plant pathogens worldwide. At present 52 Cylindrocladium spp. and 37 Calonectria spp. are recognised based on sexual compatibility, morphology and phylogenetic inference. The polyphasic approach of integrating Biological, Morphological and Phylogenetic Species Concepts has revolutionised the taxonomy of fungi. This review aims to present an overview of published research on the genera Calonectria and Cylindrocladium as they pertain to their taxonomic history. The nomenclature as well as future research necessary for this group of fungi are also briefly discussed
Biological control of Pythium aphanidermatum in cucumber with a combined application of Lysobacter enzymogenes strain 3.1T8 and chitosan
Postma, J. ; Stevens, L.H. ; Wiegers, G.L. ; Davelaar, E. ; Nijhuis, E.H. - \ 2009
Biological Control 48 (2009)3. - ISSN 1049-9644 - p. 301 - 309.
growth-promoting rhizobacteria - damping-off disease - root-rot - bacteria - plants - rhizosphere - suppression - biocontrol - rockwool - pepper
Pythium aphanidermatum (Edson) Fitzp., causing root and crown rot in cucumber, was successfully managed by Lysobacter enzymogenes strain 3.1T8. Greenhouse experiments were performed with cucumber plants grown in rockwool blocks up to 5 weeks with a recirculated nutrient solution. Application of L. enzymogenes 3.1T8 in combination with chitosan (the deacetylated derivative of chitin) reduced the number of diseased plants by 50–100% in four independent experiments relative to the Pythium control. Application of chitosan or the bacterial inoculant alone was not effective. Washed bacterial cells plus chitosan inhibited Pythium-induced disease, but the supernatant without bacterial cells combined with chitosan was not effective. The most effective and convenient type of commercially available chitosan was selected. Chitosan disappeared from the hydroponic system within 24 h after application, which we attribute to enzyme expression of L. enzymogenes 3.1T8 induced by the exposure to chitosan. Plate counts of the nutrient solution on a general bacterial medium showed the dominance of the inoculated strain, and an increased bacterial population growing on chitin and chitosan as single carbon source. The population density of L. enzymogenes 3.1T8 on the cucumber roots was investigated with a strain specific real-time TaqMan PCR. Highest chitosan concentrations applied (0.1 and 0.03 g/plant) resulted in the highest numbers of L. enzymogenes 3.1T8 present on roots; i.e. 108–109 cells/g root. Substantially higher numbers of bacterial cells were observed by scanning electron microscopy after application of chitosan; no morphological or other qualitative differences were found. The results indicate that addition of chitosan enhanced the biocontrol efficacy of L. enzymogenes 3.1T8; either chitosan serves as C- and N-source for the antagonist, induces antagonistic gene expression, or both. Keywords: Biological control; Lysobacter enzymogenes; Chitosan; Synergistic effect; Quantitative PCR; Root colonization
Control of seed-borne pathogens on legumes by microbial and other alternative seed treatments
Tinivella, F. ; Hirata, L.M. ; Celan, M.A. ; Wright, S.A.I. ; Amein, T. ; Schmitt, A. ; Wolf, J.M. van der; Koch, E. ; Groot, S.P.C. - \ 2009
European Journal of Plant Pathology 123 (2009)2. - ISSN 0929-1873 - p. 139 - 151.
colletotrichum lindemuthianum - gewasbescherming - biologische bestrijding - plantextracten - ascochyta - geïntegreerde plagenbestrijding - biologische landbouw - zaadbehandeling - plant protection - biological control - plant extracts - integrated pest management - organic farming - seed treatment - growth-promoting rhizobacteria - systemic resistance - powdery mildew - clonostachys-rosea - fusarium-culmorum - bacillus-subtilis - salicylic-acid - root-rot - biocontrol - diseases
Greenhouse trials were carried out in order to test the efficacy of different seed treatments as alternatives to chemicals against Colletotrichum lindemuthianum cause of anthracnose on bean and Ascochyta spp. cause of Ascochyta blights on pea, respectively. Resistance inducers, commercially formulated microorganisms, non-formulated selected strains of different microorganisms (fungi, bacteria and yeasts) and plant extracts were applied as dry or liquid seed treatments on naturally infested seeds. Seedling emergence and disease incidence and/or severity were recorded. Almost all seed treatments turned out to be ineffective in controlling the Ascochyta infections, which is in line with the literature stating that these pathogens are difficult to control. The only alternative treatments that gave some control of Ascochyta spp. were thyme oil and a strain of Clonostachys rosea. The resistance inducers tested successfully controlled infections of bean by C. lindemuthianum. Among the formulated microorganisms, Bacillus subtilis-based formulations provided the best protection from anthracnose. Some strains of Pseudomonas putida, a disease-suppressive, saprophytic strain of Fusarium oxysporum and the mustard powder-based product Tillecur also proved to be effective against bean anthracnose. However, among the resistance inducers as well as among the other groups, certain agents caused a significant reduction of plant emergence. Different alternative seed treatments can therefore be used for the control of C. lindemuthianum on bean, while on pea only thyme oil and a strain of Clonostachys rosea showed some effectiveness against Ascochyta spp.
Soil suppressiveness and functional diversity of the soil microflora in organic farming systems
Postma, J. ; Schilder, M.T. ; Bloem, J. ; Leeuwen, W.K. van - \ 2008
Soil Biology and Biochemistry 40 (2008)9. - ISSN 0038-0717 - p. 2394 - 2406.
rhizoctonia-solani - microbial communities - disease suppression - plant-pathogens - root-rot - pythium-aphanidermatum - bacterial - streptomyces - biocontrol - management
Arable fields of 10 organic farms from different locations in The Netherlands were sampled in three subsequent years. The soil samples were analysed for disease suppressiveness against Rhizoctonia solani AG2.2IIIB in sugar beet, Streptomyces scabies in radish and Verticillium longisporum in oilseed rape. In addition, a variety of microbial, chemical and physical soil characteristics were assessed. All data were correlated by multiple regression and multivariate analyses with the objective to find correlations between soil suppressiveness and biotic or abiotic soil characteristics. Significant differences in soil suppressiveness were found between the fields for all three diseases. Multiple regression indicated a significant correlation between suppressiveness against Rhizoctonia and the number of antagonistic Lysobacter spp., as well as with % active fungi and bacterial diversity. Grass-clover stimulated Rhizoctonia suppression as well as the presence of antagonistic Lysobacter spp. (mainly L. antibioticus and L. gummosus) in clay soils. Streptomyces suppression correlated with the number of antagonistic Streptomyces spp., % of active fungi and bacterial population size. The presence of antagonistic Streptomyces spp. correlated with a high fungal/bacterial biomass ratio. Verticillium suppression was only measured in 2004 and 2005, due to the inconsistent suppressiveness along the years. Nevertheless, a significant correlation with pH, potential nitrogen mineralization and bacterial biomass was found. Bacterial and fungal PCR-denaturing gel electrophoresis fingerprinting of bacterial and fungal communities, in general, did not significantly correlate with disease suppression. Highly significant explanatory factors of the composition of the dominating bacterial and fungal populations were % lutum, pH, C/N quotient, biomass and growth rate of bacteria. Additionally, the % of organic matter and years of organic farming were explaining significantly the composition of the bacterial population
Genetic variation among Fusarium isolates from onion, and resistance to Fusarium basal rot in related Allium species
Galván, G.A. ; Koning-Boucoiran, C.F.S. ; Koopman, W.J.H. ; Burger-Meijer, K. ; Gonzáles, P.H. ; Waalwijk, C. ; Kik, C. ; Scholten, O.E. - \ 2008
European Journal of Plant Pathology 121 (2008)4. - ISSN 0929-1873 - p. 499 - 512.
ziekteresistentie - fusarium - allium - schimmelziekten - allium cepa - onderzoek - aflp - disease resistance - fungal diseases - research - amplified fragment length polymorphism - f-sp cepae - root-rot - oxysporum - proliferatum - genealogies - cultivars - culmorum - disease - complex
The aim of this research was to study levels of resistance to Fusarium basal rot in onion cultivars and related Allium species, by using genetically different Fusarium isolates. In order to select genetically different isolates for disease testing, a collection of 61 Fusarium isolates, 43 of them from onion (Allium cepa), was analysed using amplified fragment length polymorphism (AFLP) markers. Onion isolates were collected in The Netherlands (15 isolates) and Uruguay (9 isolates), and received from other countries and fungal collections (19 isolates). From these isolates, 29 were identified as F. oxysporum, 10 as F. proliferatum, whereas the remaining four isolates belonged to F. avenaceum and F. culmorum. The taxonomic status of the species was confirmed by morphological examination, by DNA sequencing of the elongation factor 1-¿ gene, and by the use of species-specific primers for Fusarium oxysporum, F. proliferatum, and F. culmorum. Within F. oxysporum, isolates clustered in two clades suggesting different origins of F. oxysporum forms pathogenic to onion. These clades were present in each sampled region. Onion and six related Allium species were screened for resistance to Fusarium basal rot using one F. oxysporum isolate from each clade, and one F. proliferatum isolate. High levels of resistance to each isolate were found in Allium fistulosum and A. schoenoprasum accessions, whereas A. pskemense, A. roylei and A. galanthum showed intermediate levels of resistance. Among five A. cepa cultivars, `Rossa Savonese¿ was also intermediately resistant. Regarding the current feasibility for introgression, A. fistulosum, A. roylei and A. galanthum were identified as potential sources for the transfer of resistance to Fusarium into onion.
Neonectria liriodendri sp. nov., the main causal agent of black foot disease of grapevines
Halleen, F. ; Schroers, H.J. ; Groenewald, J.Z. ; Rego, C. ; Oliveira, H. ; Crous, P.W. - \ 2006
Studies in Mycology 55 (2006). - ISSN 0166-0616 - p. 227 - 234.
root-rot - cylindrocarpon
Black foot disease is a serious disease of grapevine crops in most areas where vines are grown. Mainly two species of Cylindrocarpon, C. destructans and C. macrodidymum, are associated with this disease. Recent studies have revealed a tremendous molecular variation within the former but only slight molecular variation within the latter, indicating that C. destructans presents a complex of several species The present study elucidates the taxonomic status of C. destructans-like isolates associated with black foot disease of grapevines. Grapevine isolates were studied morphologically, subjected to DNA analyses of their ITS and partial P-tubulin genes, and were mated in all combinations in vitro. Cylindrocarpon destructans strains isolated from grapevines in Europe and South Africa appeared morphologically and genetically identical, and had identical ITS and partial beta-tubulin gene sequences. Phylogenetic analyses placed these strains in a clade closely related but clearly distinct from other clades with C. destructans-like anamorphs obtained from various herbaceous or woody hosts. Only the ex-type strain of Cylindrocarpon liriodendri had identical sequences to strains isolated from grapevines, and could also not be distinguished by morphological characters. The grapevine isolates are therefore reidentified here as Cylindrocarpon liriodendri. Cylindrocarpn liriodendri formed perithecia in heterothallic conditions and the holomorph of this species is described as Neonectria liriodendri sp. nov. Neonectria liriodendri is genetically distinct from the ex-type strain of Neonectria radicicola, which originated from Cyclamen in Sweden. Both ex-type strains also differ from at least two other clades comprising additional C. destructans-like strains. Many of these strains originated from Panax sp., which is the host of the type of C. destructans. Our phylogenetic analyses indicate that C. destructans is not the anamorph of N. radicicola and that N. liriodendri, N. radicicola and several C. destructans-like taxa may have evolved independently within the same phylogenetic species complex.
How many species of fungi are there at the tip of Africa?
Crous, P.W. ; Rong, I.H. ; Wood, A. ; Lee, S. ; Glen, H. ; Botha, W. ; Slippers, B. ; Beer, W.Z. de; Wingfield, M.J. ; Hawksworth, D.L. - \ 2006
Studies in Mycology 55 (2006). - ISSN 0166-0616 - p. 13 - 33.
dna-sequence data - eucalyptus leaf fungi - south-africa - sp-nov - root-rot - interesting records - cercosporoid fungi - protea infructescences - lichen genus - rust fungi
Several recent studies have reviewed the extent of fungal biodiversity, and have used these data as basis for revised estimates of species numbers based on known numbers of plants and insects. None of these studies, however, have focused on fungal biodiversity in South Africa. Coinciding with the 100th anniversary of the National Collection of Fungi (PREM) in South Africa in 2005, it is thus timely to reflect on the taxonomic research that has been conducted in South Africa over the past Century. Information is presented on the extent of fungal collections preserved at PREM, and the associated research publications that have largely resulted from this resource. These data are placed in context of the known plant and insect biodiversity, and used as basis to estimate the potential number of fungi that could be expected in South Africa. The conservative estimate is of approximately 200 000 species without taking into account those associated with a substantial insect biodiversity.
Relation between soil health, wave-like fluctuations in microbial populations, and soil-borne plant disease management
Bruggen, A.H.C. van; Semenov, A.M. ; Diepeningen, A.D. van; Vos, O.J. de; Blok, W.J. - \ 2006
European Journal of Plant Pathology 115 (2006)1. - ISSN 0929-1873 - p. 105 - 122.
combining biocontrol agents - organic farming systems - biological-control - bacterial-populations - damping-off - root-rot - species composition - conventional farms - mycorrhizal fungi - wheat roots
A healthy soil is often defined as a stable soil system with high levels of biological diversity and activity, internal nutrient cycling, and resilience to disturbance. This implies that microbial fluctuations after a disturbance would dampen more quickly in a healthy than in a chronically damaged and biologically impoverished soil. Soil could be disturbed by various processes, for example addition of a nutrient source, tillage, or drying-rewetting. As a result of any disturbance, the numbers of heterotrophic bacteria and of individual species start to oscillate, both in time and space. The oscillations appear as moving waves along the path of a moving nutrient source such as a root tip. The phase and period for different trophic groups and species of bacteria may be shifted indicating that succession occurs. DGGE, Biolog and FAME analysis of subsequent populations in oscillation have confirmed that there is a cyclic succession in microbial communities. Microbial diversity oscillates in opposite direction from oscillations in microbial populations. In a healthy soil, the amplitudes of these oscillations will be small, but the background levels of microbial diversity and activity are high, so that soil-borne diseases will face more competitors and antagonists. However, soil-borne pathogens and antagonists alike will fluctuate in time and space as a result of growing plant roots and other disturbances, and the periods and phases of the oscillations may vary. As a consequence, biological control by members of a single trophic group or species may never be complete, as pathogens will encounter varying populations of the biocontrol agent on the root surface. A mixture of different trophic groups may provide more complete biological control because peaks of different trophic groups occur at subsequent locations along a root. Alternatively, regular addition of soil organic matter may increase background levels of microbial activity, increase nutrient cycling, lower the concentrations of easily available nutrient sources, increase microbial diversity, and enhance natural disease suppression.
Characterization of the microbial community involved in the suppression of Pythium aphanidermatum in cucumber grown on rockwool
Postma, J. ; Geraats, B.P.J. ; Pastoor, R. ; Elsas, J.D. van - \ 2005
Phytopathology 95 (2005)7. - ISSN 0031-949X - p. 808 - 818.
gradient gel-electrophoresis - 16s ribosomal-rna - biological-control - root-rot - rhizoctonia-solani - pcr-dgge - soil - rhizobacteria - regimes - plants
The root pathogen Pythium aphanidermatum induced lower levels of disease in cucumber (Cucumis sativus) plants on unsterilized, re-used rockwool slabs than on heat-sterilized, re-used rockwool. Several recolonization treatments of the sterilized rockwool enhanced the suppressiveness of the rockwool. Microbial community structures in the different rockwool treatments were investigated by plate counts on selective media. Disease suppressiveness in the different rockwool treatments showed the highest correlation with the culturable number of filamentous actinomycetes in both experiments (r = 0.79 and 0.94), whereas the numbers of Trichoderma spp. correlated with suppression only in the first experiment (0.86). The numbers of total culturable bacteria, fluorescent pseudomonads, Bacillus spores, and fungi all showed lower correlations with disease suppressiveness. The filamentous actinomycetes enumerated with the plate counts were mainly Streptomyces spp., of which 10% were antagonistic toward P. aphanidermatum in dual culture. The composition of the bacterial and actinomycete populations was studied with polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE). Multivariate analyses of these patterns with canonical correspondence analysis showed significant correlations between the microbial composition and the disease suppressiveness. However, none of the bands in PCR-DGGE patterns occurred exclusively in the treatments that had enhanced disease suppressiveness. Bands extracted from the actinomycete-specific DGGE gels showed closest similarity with members of several actinomycete genera, i.e., Streptomyces, Mycobacterium, Microbacterium, Rhodococcus, Curtobacterium, and Tsukamurella. The possible mechanism of disease suppressiveness in used rockwool slabs, based on the results obtained with culture-dependent and culture-independent detection methods, is discussed. Additional keywords: community profiling, root and crown rot
Production of antifungal compounds by Lysobacter enzymogenes isolate 3.1.T8 under different conditions in relation to its efficacy as a biocontrol agent of Pythium aphanidermatum in cucumber
Folman, L.B. ; Klein, M.J.E.I.M. de; Postma, J. ; Veen, J.A. van - \ 2004
Biological Control 31 (2004)2. - ISSN 1049-9644 - p. 145 - 154.
burkholderia-cepacia ammdr1 - mediated gene-regulation - biological-control - pseudomonas-fluorescens - damping-off - root-rot - oomycete pathogens - plant-pathogens - in-vitro - bacteria
Lysobacter enzymogenes strain 3.1T8 is a potential biocontrol agent of Pythium aphanidermatum (Edson) Fitzp. in cucumber (Cucumis sativa L.). It showed in vitro antagonistic activity, hemolytic activity, and the production of a surface active compound, which decreased in media of increasing strength. One or more low molecular compounds, present in culture filtrates of 3.1T8, caused rapid immobilization of zoospores of P. aphanidermatum and inhibited cyst germination. Bioassays for suppression of root and crown rot were performed with 2-week-old cucumber plants in nutrient solution. Complete disease suppression occurred after addition of a suspension of unwashed cells grown on nutrient-poor R2A, or the filtrate of this suspension, 1 day before inoculation with zoospores. Application of washed cells caused slight suppression in one of two bioassays only. No disease suppression occurred when bacterial inoculum grown on 1/10 TSBA or in 1/10 TSB was used. In two bioassays on cucumber plants grown for 4¿5 weeks in 18-L containers, application of R2A-grown cells of 3.1T8 did not cause disease suppression. Density of 3.1T8, monitored using immunofluorescence colony staining, decreased at least 100-fold during these experiments to approximately log 3¿4 cfu ml¿1 of nutrient solution and log 5¿6 cfu g¿1 roots. Overall, the findings indicated a strong influence of nutritional resources on production of antifungal compounds by strain 3.1T8. The lack of disease suppression in hydroculture containers suggested that in situ production of the compounds was insufficient or absent, although the bacteria persisted in the nutrient solution and on the roots of cucumber
Characterization of Armillaria isolates from tea (Camellia sinensis) in Kenya
Otieno, W. ; Perez Sierra, A. ; Termorshuizen, A.J. - \ 2003
Mycologia 95 (2003)1. - ISSN 0027-5514 - p. 160 - 175.
mellea complex - species delimitation - mitochondrial dnas - genetic diversity - causal agent - black line - root-rot - identification - africa - polymorphisms
Armillaria is a primary root rot pathogen of tea (Camellia sinensis) in Kenya. The main species presently described in this country are A. mellea and A. heimii. A survey covering fourteen districts of Kenya was carried out and forty-seven isolates of Armillaria collected. Cultural morphology, rhizomorph characteristics, somatic incompatibility and features of basidiomata were used to characterize the isolates, together with molecular analysis based on randomly amplified polymorphic DNA (RAPD), inter-simple sequence repeat (ISSR), restriction fragment length polymorphism (RFLP) of the internal transcribed spacer (ITS) and the intergenic spacer (IGS) regions and sequence of the IGS region. It can be concluded that two Armillaria species were present and they were different from A. mellea. The first group was morphologically similar to A. heimii but this was contradicted by the molecular data, suggesting that A. heimii could be a complex of several species. The second group was different from the first and morphological and molecular data strongly suggest that it could be a new Armillaria species.
Inability to Find Consistent Bacterial Biocontrol Agents of Pythium aphanidermatum in Cucumber Using Screens Based on Ecophysiological Traits
Folman, L.B. ; Postma, J. ; Veen, J.A. van - \ 2003
Microbial Ecology 45 (2003)1. - ISSN 0095-3628 - p. 72 - 87.
growth-promoting rhizobacteria - burkholderia-cepacia ammdr1 - biological-control - root-rot - enterobacter-cloacae - oomycete pathogens - induced resistance - damping-off - pseudomonas - soil
A collection of 821 rhizobacteria from cucumber, originating from different root locations and stages of plant development, was screened for potential biocontrol agents of Pythium aphanidermatum (Edson) Fitzp. The screening procedure exploited carbon source utilization profiles and growth rates of bacteria as indicators of a partial niche overlap with the pathogen. The bacteria were tested for growth on nine carbon sources (glucose, fucose, sucrose, maltose, asparagine, alanine, galacturonic acid, succinic acic, and linoleic acid), most of which are reported to be used by the zoospores of P. aphanidermatum in the infection process. The isolates were classified as fast- or slow-growing, depending on their growth rate in 1/10 strength TSB. By nonhierarchical cluster analysis, 20 clusters were generated of bacteria with similar profiles of carbon source utilization. Redundancy analysis showed that the type of root sample explained 47 f the variance found in the relative abundance of bacteria from the clusters. Bacteria from clusters using none or few of the carbon sources, e.g., maltose and linoleic acid, with many slow-growing isolates, showed a preference for plants in the vegetative or generative stage, or for old root regions (root base). Bacteria from clusters with fast-growing isolates, using many carbon sources, were relatively abundant in the seedling stage. A selection of 127 bacteria from the different clusters was tested for disease suppressive capabilities in bioassays on young cucumber plants in nutrient solution, inoculated with zoospores of P. aphanidermatum. Nine of these bacteria produced biosurfactants, and 27 showed antibiosis against mycelial growth in plate assays. For 31 isolates, significant positive effects on plant biomass were shown, as analyzed with a general linear regression model. For most isolates, these effects occurred only in one of two replicate assays and no reductions in the degree of root and crown rot were found. Of the isolates that used many of the tested carbon sources, only four had positive effects on plant biomass. The majority of the isolates that positively affected plant biomass used few to moderate numbers of carbon sources and did not produce antibiotics or biosurfactants. In conclusion, competition for the tested carbon sources with the zoospores did not play a decisive role in disease suppression, and no clear relation was found between ecophysiological traits and disease suppression. Only isolate 3.1T8, isolated from root tips in the generative stage of plant growth, significantly increased plant biomass and suppressed root and crown rot symptoms in five out of six bioassays. The isolate produced an antifungal substance in plate assays and showed biosurfactant production in several (cucumber-derived) media.
A greenhouse test for screening sugar beet (Beta vulgaris) for resistance to Rhizoctonia solani
Scholten, O.E. ; Panella, L. ; Bock, T.S.M. de; Lange, W. - \ 2001
European Journal of Plant Pathology 107 (2001)2. - ISSN 0929-1873 - p. 161 - 166.
anastomosis groups - root-rot - pathogenicity
Rhizoctonia solani Kühn is a serious plant pathogenic fungus, causing various types of damage to sugar beet (Beta vulgaris L.). In Europe, the disease is spreading and becoming a threat for the growing of this crop. Plant resistance seems to be the most practical and economical way to control the disease. Experiments were carried out to optimise a greenhouse procedure to screen plants of sugar beet for resistance to R. solani. In the first experiment, two susceptible accessions were evaluated for root and leaf symptoms, after being grown in seven different soil mixtures and inoculated with R. solani. The fungus infected all plants. It was concluded that leaf symptoms were not reliable for the rating of disease severity. Statistically significant differences between the soil mixtures were observed, and there were no significant differences between the two accessions. The two soil mixtures, showing the most severe disease symptoms, were selected for a second experiment, including both resistant and susceptible accessions. As in the first experiment, root symptoms were recorded using a 1¿7 scale, and a significant expression of resistance was observed. The average severity of the disease in the greenhouse experiment generally was comparable with the infection in field experiments, and the ranking of the accessions was the same in the two types of experiments. It was concluded that evaluation procedures in the greenhouse could be used as a rapid assay to screen sugar beet plants for resistance to R. solani
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