European Journal of Plant Pathology

Published by Springer Verlag
Online ISSN: 1573-8469
Publications
Article
In the past the root rot pathogen Roesleria subterranea (Ascomycota) was generally considered as a minor parasite, a view with which we were often confronted during field work in German wine-growing regions where this ascomycete recently caused serious problems in established vineyards and at replant sites. To irrevocably demonstrate that R. subterranea is not a minor, but a primary pathogen of grapevines (and fruit trees) a pest risk analysis was carried out according to the guidelines defined by EPPO standard series PM 5, which defines the information needed, and contains standardised, detailed key questions and a decision support scheme for risk analysis. Following the provided decision scheme, it becomes apparent that R. subterranea must be considered as a serious, primary pathogen for grapevines and fruit trees that can cause massive economic losses. Based on the literature, the pathogen seems to be ubiquitous in wine growing regions in cool climates of the northern hemisphere. It is likely that because of its growth below ground, the small fruiting bodies, and ambiguous symptoms above ground, R. subterranea has been overlooked in the past and therefore, has not been considered as primary pathogen for grapevine. Available published information together with experience from field trials was implemented into a diagnostic decision scheme which will, together with the comprehensive literature provided, be the basis (a) to implement quick and efficient diagnosis of this pathogen in the field and (b) to conduct risk analysis and management in areas where R. subterranea has not established yet.
 
Article
The inhibitory effects of Chinese leek(Allium tuberosum) on Fusarium oxysporum f. sp. cubense (Foc) and on Fusarium wilt incidence were studied in order to identify a potential efficient way to control the disease. Adopting the rotation system of Chinese leek-banana reduced the Fusarium wilt incidence and disease severity index by 88 %-97 % and 91 %-96 %, respectively, improved the crop value by 36 %-86 %, in an area heavily infested by Foc between 2007 and 2009. As a result of inoculation in the greenhouse, Chinese leek treatment reduced disease incidence and the disease severity index by 58 % and 62 %, respectively in the variety Baxi (AAA) and by 79 % and 81 %, respectively in the variety Guangfen NO.1 (ABB). Crude extracts of Chinese leek completely inhibited the growth of Foc race 4 on Petri dishes, suppressed the proliferation of the spores by 91 % and caused 87 % spore mortality. The findings of this study suggest that Chinese leek has the potential to inhibit Foc growth and Fusarium wilt incidence. This potential may be developed into an environmentally friendly treatment to control Fusarium wilt of banana.
 
Article
Rice bacterial blight (BB), caused by Xanthomonas oryzae pv. Oryzae (Xoo), is a serious disease in rice production worldwide. Rice cv. Zhenhui 084, a newly developed strong indica restorer line, exhibits high resistance to most of the Philippine races of BB and has been widely used in rice hybrids in China; however, the resistance gene has not yet been cloned. Here, we show that the resistance of Zhenhui 084 to Xoo strains is similar to that of IRBB7 containing Xa7, a durable and broad resistance dominant gene for BB. To map the resistance gene in Zhenhui 084, a F2 population with 331 highly susceptible individuals derived from a cross between Chenghui 448 and Zhenhui 084 was built. We finely mapped the target R gene to a region between two proximal markers RM20576 and MY4 in rice chromosome 6. A marker-based physical map of chromosome six was used to construct the contig covering the genomic region between two markers RM20576 and MY4. The target gene was assumed to be in an interval of approximate 200kb, in which 16 candidate genes were predicted. Our findings will greatly facilitate the isolation and characterisation of the target R gene allelic to Xa7. Additionally, two PCR-based markers, tightly linked to the target R gene locus, will be a useful tool for the marker-assisted selection of the target R gene allelic to Xa7 in breeding programmes.
 
Article
The compounds referred to in the title have been investigated for fungicidal, insecticidal and acaricidal activities in laboratory and greenhouse tests. Several representatives of this class of compounds were active against powdery mildew on apple, cucumber, and barley, and against aphids and spider mites, both when applied to the leaves and when added to the nutrient solutions of test plants. Treatment of leaf halves resulted in protection of the entire leaves. A striking difference in pesticidal activity was observed between two series of isomers. Representatives of the series with the phosphoryl group in the 1-position showed much greater pesticidal activities than their corresponding isomers with the phosphoryl group in the 2-position. The optimum activity within the two homologous series (R-H, CH3 ... C6H13) was determined: generally the lower homologues (R-H, CH3, C2H5 and i-C3H7) showed the greatest pesticidal activity in the systemic tests. After leaf-application the influence of the length of R was less pronounced or even reversed. © 1968 Koninklijke Nederlandse Planteziektenkundige Vereniging.
 
Article
In this study, the biocontrol ability of seven grapevine-associated bacteria, previously reported as efficient against Botrytis cinerea under in vitro conditions, was evaluated in two vineyard orchards with the susceptible cv. Chardonnay during four consecutive years (2002–2005). It was shown that the severity of disease on grapevine leaves and berries was reduced to different levels, depending on the bacterial strain and inoculation method. Drenching the plant soil with these bacteria revealed a systemic resistance to B. cinerea, even without renewal of treatment. Accordingly, this resistance was associated with a stimulation of some plant defense responses such as chitinase and β-1,3-glucanase activities in both leaves and berries. In leaves, chitinase activity increased before veraison (end-July) while β-1,3-glucanase reached its maximum activity at ripening (September). Reverse patterns were observed in berries, with β-1,3-glucanase peaking at full veraison (end-August) and chitinase at a later development stage. Highest activities were observed with Acinetobacter lwoffii PTA-113 and Pseudomonas fluorescens PTA-CT2 in leaves, and with A. lwoffii PTA-113 and Pantoea agglomerans PTA-AF1 in berries. These results have demonstrated an induced protection of grapevine against B. cinerea by selected bacteria under field conditions, and suggest that induced resistance could be related to a stimulation of plant defense reactions in a successive manner.
 
Article
Differential resistance of pearl millet cultivars to downy mildew disease was correlated with the levels of -1,3-glucanase in their seeds. Higher activity of the enzyme in highly resistant cultivars and lower activity in the highly susceptible ones suggested the possible use of -1,3-glucanase as a biochemical marker for screening pearl millet cultivars for downy mildew disease. Inoculation of seedlings with the downy mildew pathogen Sclerospora graminicola resulted in increased enzyme levels in resistant cultivars. Mesocotyl and shoot regions of seedlings recorded higher levels of enzyme than the root. Isoelectric focusing revealed four basic isoforms with pI 9.6, 9.0, 8.9 and 8.2 and two acidic isoforms with pI 4.9 and 6.2 of -1,3-glucanase in pearl millet. The pI 9.6 isoform was a major isoform of the enzyme in the pearl millet seedlings with a probable developmental function. Isoforms pI 6.2 and pI 8.2 appeared to be involved in resistance and pI 4.9 isoform seemed to be involved in pathogenesis of pearl millet-downy mildew.
 
Article
There were indications that endo-1,3--glucanase (1,3-(1,3;1,4)--D-Glucan 3(4)-glucanohydrolase (EC 3.2.1.6)) and cellulase (1,4-(1,3;1,4)--D-Glucan 4-glucanohydrolase (EC 3.2.1.4)) activity of Trichoderma harzianum Rifai isolate T3 were induced in sphagnum peat moss cultivations and dual culture experiments by the presence of Pythium ultimum. Further, P. ultimum stimulated the germination of Trichoderma conidia. Endo-1,3--glucanase and cellulase were purified from T. harzianum isolate T3, known to control Pythium damping-off of cucumber seedlings. The enzymes were purified from the culture filtrate of the fungus by gel filtration and isoelectric focusing. The purified endo-1,3--glucanase was a small protein with a molecular mass of 17 kilodaltons and a pI of 5.0. Two cellulases were purified to homogeneity and had molecular masses of 40 and 45 kilodaltons respectively, and pI's of 6.4 and 7.6 respectively. Germination of encysted zoospores and elongation of germ tubes of a plant pathogenic Pythium isolate were inhibited by low concentrations of the purified enzymes. A strong synergistic effect was observed on the inhibition of cyst germination by a combination of the endo-1,3--glucanase and the fungicide Fongarid. Finally, a time-course study of colonization of the rhizosphere of cucumber seedlings showed that the active fungal mycelial biomass of a GUS-transformant of T. harzianum isolate T3 increased over four weeks. Trichoderma appeared to colonize healthy roots only superficially, whereas the mucilage of the root hairs and of distal parts of wounded areas or broken parts of the roots, were extensively colonized.
 
Article
Genes encoding an acidic wheat class IV chitinase (383), an acidic wheat β 1,3-glucanase (638) and a rice cationic peroxidase (POC1) were introduced into ‘Nantes Coreless’ carrot (Daucus carota) by Agrobacterium-mediated transformation. The genes were introduced singly or in various combinations followed by selection imposed by the herbicide phosphinothricin. Regenerated plantlets were screened for presence and expression of the three transgenes using PCR, Southern and Northern hybridisations. Eighteen transgenic lines expressing a single transgene and 2 lines each co-expressing 638/383 and 383/POC1 were assessed for resistance to the necrotrophic fungal pathogens Botrytis cinerea and Sclerotinia sclerotiorum. Percentage leaf area diseased was measured 4 and 7days after inoculation (dai) and compared to non-transformed control plants. Six lines expressing β-1,3-glucanase 638 alone had no enhanced resistance to B. cinerea at 4dai and only slight resistance to S. sclerotiorum; there was no effect at 7dai. Two out of the six lines expressing 383 alone had enhanced tolerance to both pathogens with a 20–50% reduction in disease development at 7dai. Two lines co-expressing 638/383 had slight reductions in disease by (10–20%) similar to that of the lines expressing chitinase 383 alone. Highest levels of disease resistance were seen in transgenic lines expressing POC1, alone or in combination with chitinase 383. Disease symptoms were slower to develop and symptoms were reduced by up to 90% for B. cinerea and 70% for S. sclerotiorum. The 383/POC1 co-expressing plants developed disease at levels similar to that of POC1 alone. Petioles of plants over-expressing POC1 had higher levels of lignin accumulation constitutively compared to control plants, which was greatly enhanced following inoculation with S. sclerotiorum. These results indicate that peroxidase over-expression can lead to significant disease reduction against necrotrophic pathogens in transgenic carrot plants.
 
Putative sources and functions of reactive oxygen species (ROS) in host–pathogen interactions of biotrophic and necrotrophic organisms
Accumulation of H2O2 as seen by DAB-staining (Thordal-Christensen et al. 1997) in the barley–B. graminis f.sp. hordei interaction (a, b) and the wheat–S. tritici interaction (c, d). a shows barley isoline P-01 inoculated with isolate c15. A cell is undergoing HR as a response to penetration and is completely stained with DAB. b shows barley isoline P-02 inoculated with isolate c15, 2 days after inoculation. Note red–brown staining in the papillae and that the papilla in the cell containing an haustorium is not stained with DAB whereas the other papillae are stained. c shows wheat cv. Stakado inoculated with isolate IPO323 of S. tritici (incompatible interaction) at 5 days after inoculation. H2O2 is accumulating in the apoplast of the substomatal cavity of a stoma penetrated by the pathogen. d shows wheat cv. Sevin inoculated with isolate IPO323 of S. tritici (compatible interaction) at 15 days after inoculation. H2O2 is accumulating throughout the tissue in which fungal sporulation occurs
Article
The production of reactive oxygen species (ROS) by the consumption of molecular oxygen during host–pathogen interactions is termed the oxidative burst. The most important ROS are singlet oxygen (1O2), the hydroxyperoxyl radical (HO2·), the superoxide anion ( \textO\text2 - )\left( {{\text{O}}_{\text{2}} ^ - } \right), hydrogen peroxide (H2O2), the hydroxyl radical (OH-) and the closely related reactive nitrogen species, nitric oxide (NO). These ROS are highly reactive, and therefore toxic, and participate in several important processes related to defence and infection. Furthermore, ROS also play important roles in plant biology both as toxic by-products of aerobic metabolism and as key regulators of growth, development and defence pathways. In this review, we will assess the different roles of ROS in host–pathogen interactions with special emphasis on fungal and Oomycete pathogens.
 
Article
This review describes the naturally occurring mechanisms in cereals that lead to a reduction of Fusarium trichothecene mycotoxin accumulation in grains. A reduction in mycotoxin contamination in grains could also limit fungal infection, as trichothecenes have been reported to act as virulence factors. The mechanisms explaining the low toxin accumulation trait, generally referred to as type V resistance to Fusarium, can be subdivided into two classes. Class 1 includes mechanisms by which the plants chemically transform the trichothecenes, leading to their degradation or detoxification. Among the detoxification strategies, glycosylation of trichothecenes is a natural process already reported in wheat. According to the structure and the toxicity of trichothecenes, two other detoxification processes, acetylation and de-epoxidation, can be expressed, at least in transgenic plants. Class 2 comprises mechanisms that lead to reduced mycotoxin accumulation by inhibition of their biosynthesis through the action of plant endogenous compounds. These include both grain constitutive compounds and compounds induced in response to pathogen infection. There are already many compounds with antioxidant properties, like phenolic compounds, peptides or carotenoids, and with prooxidant properties, like hydrogen peroxide or linoleic acid-derived hydroperoxides, that have been described as ‘modulators’ of mycotoxin biosynthesis. This review addresses for the first time different studies reporting specific in vitro effects of such compounds on the biosynthesis of Fusarium mycotoxins. A better understanding of the natural processes limiting accumulation of trichothecenes in the plant will open the way to the development of novel breeding varieties with reduced ‘mycotoxin risk’.
 
(continued)
List of the symptomatic ash samples tested in this study and results following isolation and real-time PCR assays targeting C. fraxinea ITS and 18S rDNA region Sample Origin Tissue analysed C. fraxinea isolation RT-PCR C. fraxinea a RT-PCR DNA control ab
Article
Chalara fraxinea is a fungus currently threatening ash trees (Fraxinus excelsior) in several European countries. This emerging pathogen was assigned to the EPPO’s alert list and therefore accurate detection and identification tools are needed. Because of its slow growth rate on agar media and the frequent presence of fast-growing saprotrophic fungi within the host tissue, classical isolation techniques are time-consuming and sometimes inefficient. In this study, we used species-specific polymorphisms observed within the internal transcribed spacer region to design a primer pair and a dual-labelled probe to be used in a real-time PCR assay for the detection of C. fraxinea. The test proved to be specific, based on in silico and in vitro assessments, and could detect as little as 20fg of C. fraxinea DNA. A protocol was developed in order to detect the pathogen directly in plant tissue and proved to be more efficient and rapid than isolation on agar plates. This new tool should be useful both for monitoring and to conduct epidemiology research on this emerging pathogen.
 
Family means (and range of variation) of early performance and susceptibility variables of 39 Pinus pinaster open pollinated families and one unimproved seed source (TC)
Pearson correlation matrix among early performance and susceptibility variables in 40 Pinus pinaster open pollinated families
Article
Results of a greenhouse Armillaria ostoyae inoculation experiment, designed for screening resistant Pinus pinaster genotypes and for exploring the role of different phenotypic traits in seedling susceptibility, are reported. The experiment included 39 open-pollinated pine families that comprised a random subset of the breeding population of P. pinaster in Galicia (NW Spain). We employed a non-parametric survival-time analysis to analyze patterns of survival times during 14months after inoculation with a local A. ostoyae strain. Results indicate (i) a significant correlation between seed weight and tree susceptibility, with seedlings originating from large seeds being more susceptible, (ii) a positive family mean correlation between secondary root weight and size and median life expectancy, and (iii) genetic variation of tree tolerance to A. ostoyae, with some families surviving significantly longer than others. Less susceptible families could be used in breeding programmes or directly in forest plantations to reduce the losses caused by A. ostoyae. Large within-family variation in tolerance to the disease was also observed, suggesting that non additive genetic variance was also important. Although being infected, 32 out of the 1200 inoculated trees survived the fungus infection. These tolerant genotypes comprise an attractive collection to further investigate genetic, phenotypic and environmental factors affecting pine susceptibility to Armillaria root rot. KeywordsTree resistance–Pine–Screening–White root rot–Root density
 
Article
Cereal eyespot fungi Tapesia acuformis and Tapesia yallundae are closely related species which show different behaviours upon treatment with sterol 14-demethylase inhibitors (DMIs). T. acuformis is naturally resistant to DMIs belonging to the triazole family and susceptible to the imidazole ones, whilst T. yallundae is sensitive to both inhibitors. Cloning of the target enzyme gene, CYP51, from the two species revealed an important polymorphism between them. Further sequencing of CYP51 from sixteen T. acuformis and eleven T. yallundae strains with different phenotypes with regards to resistance to DMIs confirmed that at least eleven variations are species related. Among them, a conserved phenylalanine residue at position 180, found both in T. yallundae and in all known CYP51 proteins from filamentous fungi and yeast, was replaced in T. acuformis by a leucine. Therefore, a leucine at 180 could be possibly involved in natural resistance of T. acuformis to triazoles. Other mutations were observed in some resistant strains, sometimes simultaneously, but in contrast to what was reported for other filamentous fungi, where a mutation at the 136 position of the CYP51 gene product seemed to correlate with resistance to DMIs, we did not find a clear relationship between a given mutation and a particular phenotype. This result suggests that resistance to DMIs could have a polygenic nature in Tapesia. We took advantage of species-related variations to develop a PCR-based assay allowing rapid and easy discrimination between field strains of the two species.
 
Article
Eight different strains of TMV were used to inoculate tomato plants when the first truss was in flower. The proportion of the seeds infected by TMV was highest with the enation strain followed by tomato and winter necrosis strains. The other strains, viz. yellow ringspot, yellow mosaic, crusty fruit and tobacco strains and the symptomless mutant MII-16, either resulted in a low proportion of seeds with TMV or none at all. MII-16-inoculated plants consistently gave the lowest proportion of TMV-infected seeds. The possibility of using this strain to produce virus-free seeds is discussed.
 
Article
De bruikbaarheid van een door inwerking van salpeterigzuur verkregen, symptoomloze mutant van het tabaksmozaïekvirus (TMV) is gebleken uit een volledige bescherming van planten tegen een infectie met andere stammen van het virus en uit bevredigende proefresultaten onder praktijkomstandigheden. Het probleem doet zich voor dat de mutant in feite deel uitmaakt van een stammenmengsel, waarbinnen de verhoudingen echter ten gunste van de mutant zijn te beïnvloeden. © 1972 Koninklijke Nederlandse Planteziektenkundige Vereniging.
 
Representative multiplex PCR results in surveys for R. solanacearum in potato seed samples. Lanes 1-8, DNA of various potato seed samples; lane 9, DNA of potato extracts mixed with C. michiganensis subsp. sepedonicus cells (2 × 10 5 ); lane 10, DNA of potato extracts mixed with R. solanacearum (NCPPB 1331) cells (2×10 5 ); lane 11, genomic DNA of R. solanacearum (NCPPB 1331); lane 12, negative control; lanes M, DNA size marker (100 bp ladder, Life Technologies, Germany).
Bacterial strains used in this study
Restriction analysis of multiplex PCR products digested with Bsm I (Boehringer Mannheim, Germany). Lanes 1 and 2, undigested and digested R. solanacearum division 2-specific PCR products respectively; lanes 3 and 4, undigested and digested multiplex PCR products of a R. solanacearumpositive potato sample; lanes 5 and 6, undigested and digested plant-specific universal PCR product; lanes M, DNA size marker (100 bp ladder, Life Technologies, Germany).
Primer sequences and sizes of amplified DNA-fragments
Article
Polymerase chain reaction (PCR) methods for detection and differentiation of Ralstonia solanacearum strains were compared. The 16S–23S rRNA gene ITS sequence data revealed the two main sequence clusters (divisions I and II) of R. solanacearum and further subclusters of division II. Based on this sequence data, primers were designed which differentiated divisions I and II. Furthermore, to improve reliability of the PCR assay for routine detection of R. solanacearum in host plants, a novel multiplex PCR assay was developed in which the pathogen-specific sequences are coamplified with host plant DNA as an internal PCR control (IPC). The assay was validated during routine testing of potato samples submitted in official surveys. Of 4300 samples from 143 cultivars, 13 tested positive in both multiplex PCR and immunofluorescence (IF) assays and could be confirmed by bioassay in tomato seedlings and reisolation of the pathogen. The IPC was successfully amplified from all samples tested. A further 12 samples gave positive IF results which were not confirmed by either the multiplex PCR or tomato bioassay, indicating a greater specificity of the latter two assays.
 
Sequence homology among 16S rDNA from ArAWB phytoplasma and strains from groups 16SrVII (EriWB, Ash1, Ash3, Ash5, LWB); 16SrV (EY1, ULW) and unidentified mollicute (BLL) 
Symptomatic alfalfa plant (Medicago sativa) affected by ArAWB phytoplasma. Severely reduced leaf size as well as shoot shortness can be seen in diseased plants.  
RFLP analysis of 1.8-kb PCR product (P1/P7 primers) of AshY1 Reference Strain (RS), San Martı´nMartı´n ArAWB isolate (SM) and Pocito ArAWB isolate (P) were digested with AluI, HinfI, HhaI, RsaI, and TaqI restriction enzymes. M: 100 bp DNA ladder (New England Biolabs Inc.) (100, 200, 300, 400, 500, 517, 600, 700, 800, 900, 1000, 1200 and 1517 bp).  
Similarity coefficients derived from putative RFLP analysis of 16S rDNA of ArAWB phytoplasma and the most closely related phytoplasmas belonging to groups 16SrVII (EriWB, Ash1, Ash3, Ash5, LWB); 16SrV (EY1, ULW) and unidentified mollicute (BLL)
Phylogenetic tree constructed by parsimony of 16S rRNA gene sequences from 13 phytoplasmas and Acholeplasma palmae as the outgroup. The numbers on the branches are bootstrap (confidence) values. The strains used in the analysis are the following: 'Ca. P. fraxini' LWB3 (Lilac witches¢-broom;); 'Ca. P. fraxini' AshY1 (Ash yellows 1); 'Ca. P. fraxini' AshY3 (Ash yellows 3); 'Ca. P. fraxini'' AshY5 (Ash yellows 5); ArAWB (argentinean alfalfa witches¢-broom); EriWB (erigeron witches¢-broom); BLL (brinjal little leaf); CP (clover proliferation); EY1 (elm yellows;); ULW (elm yellows); FD (flavescence doree); ALY (alder yellows ) and RuS (rubus stunt).  
Article
A phytoplasma infecting alfalfa crops was detected and characterised in Argentina, the Argentinean Alfalfa witches′-broom (ArAWB) phytoplasma. Typical witches′-broom symptoms were observed in diseased alfalfa plants from fields of the ‘Cuyo’ region in the Andean midwest. Pleomorphic bodies were observed by electron microscopy in sieve tubes of the diseased plants. The results obtained from the sequence homology, similarity coefficients derived from RFLP of the 16S rDNA and phylogenetic analysis led us to include this phytoplasma in the 16Sr VII (Ash Yellows) group. However, the ArAWB phytoplasma showed several differences when compared to other members of group 16Sr VII. The RFLP analysis of partial 16S rRNA gene of two ArAWB isolates, digested with 16 restriction enzymes, showed differences between the ArAWB and the reference strain (AshY1T) in six enzyme patterns. Restriction patterns unique for the group and an exclusive HinfI restriction site were found in the ArAWB phytoplasma rDNA. Moreover, the similarity coefficients (0.92–0.86) were lower than those obtained among other group members. The significant differences detected suggested that this phytoplasma belonged to a subgroup different from those described so far. We propose therefore, that the ArAWB phytoplasma should be included in a new VII-C subgroup, closely related to the EriWB phytoplasma (VII-B) described in Brazil.
 
Article
New Xanthomonas isolates causing citrus bacterial canker in Korea were differentiated primarily on the basis of host range by comparison with reference strains. The new isolates were pathogenic to Citrus sinensis, C. paradisi, C. limon and C. unshiu and formed crater-like canker on the plants; this indicated that they were X. axonopodis (X.a.) pv. citri A types. Molecular characterization using rep-PCR fingerprinting and 16S rDNA sequence analysis was also performed. Cluster analysis by combining the band patterns of ERIC-, BOX- and REP-PCR clearly separated one group including only X. a. pv. citrumelo and the other group including X. a. pv. citri and X. a. pv. aurantifolii strains. There was a clear separation between X. a. pv. citri Asiatic types and X. a. pv. aurantifolii B, C types in the second group. Partial sequence analysis of 16S rDNA revealed that all strains of X. a. pv. aurantifolii B and C type, and X. a. pv. citrumelo formed a distinct cluster with a similarity of 99%. Our results indicate that the isolates causing citrus canker in Korea belong to the A type of X. a. pv. citri.
 
Reactions of MAb Cmm1 with surface antigens of Cmm cells (a and b) and microcolonies (c). Electron micro- graphs of Cmm strain CM761 incubated with colloidal gold-labelled MAb Cmm1 (a and b) and immunofluorescence colony staining of Cmm microcolonies using FITC-conjugated MAb Cmm1 (c). 
Titration curves for MAb Cmm1. Data for Cmm strains CM761 (s), A518-1 (h) and B100 (d), Cms strain ATCC 9850 (n), Curtobacterium flaccumfaciens strain ATCC 6887 (D), Pantoea herbicola strain Eh-1 (m) and an unidentified, non-pathogenic seed saprophyte A518-8A (+) were generated using formalinized cells in an indirect ELISA.
Seed lots tested for Cmm infestation
Characterization of 236 geographically diverse Cmm strains by ELISA and bioassays on tomato (cv. Kewalo)
Article
Specificity of a monoclonal antibody (MAb), Cmm1, to geographically diverse strains of the seed-borne tomato pathogen, Clavibacter michiganensis subsp. michiganensis (Cmm), was assessed and the MAb was tested for its usefulness as a tool to separate the pathogen from saprophytes in naturally infested tomato seed. Of the 236 international Cmm strains tested, 99% reacted with MAb Cmm1. MAb Cmm1 was also strongly reactive with an additional 32 strains isolated from seed that were later identified as Cmm by the Biolog MicroLog™ microbial identification system (Biolog, Inc., Hayward, CA) and 16S rDNA sequence analysis. It correctly differentiated these strains from 12 MAb Cmm1-negative seed strains that possessed similar colony morphology but were later identified as other Gram-positive genera and species. The specificity of MAb Cmm1 to the pathogen and the near universality of the MAb Cmm1-reactive antigen among diverse Cmm strains make this antibody a useful detection and identification tool. The finding that a large proportion of the Cmm strains associated with naturally infested tomato seed were putatively hypovirulent or non-virulent indicates that such populations cannot be ignored and points to a need for studies to determine their significance in host-pathogen interactions.
 
Symptoms of HLB disease on indicator plants (22 weeks after grafting): a Healthy ponkan. b Small-sized yellow leaves caused by Gd-ltc. c Yellow leaves with narrow blades typically caused by Cq-tk. d Symptoms resembling nutritional deficiency caused by Hn-bjnm. e Leaf yellowing caused by Cq-qj. f Blotchy mottling caused by Jx-gc  
Agarose gel electrophoresis of 16S rDNA digested with restriction enzyme XbaI. M,100 bp DNA ladder marker VII (SD015-2, Dingguo); lane 1, Gd-pg; lane 2, Gd-hp; lane 3, Gxsty ; lane 4, Gx-nn; lane 5, Hn-bjnm; lane 6, Fj-nhe; lane 7, Cqtk ; lane 8, Hn-ng; lane 9, Jx-gcF. Blotchy mottling caused by Jx-gc  
Article
Phylogenetic analysis of Chinese isolates of the citrus Huanglongbing (HLB) bacterium based on the 16S rDNA and 16S/23S rDNA intergenic regions sequences was carried out. Nine HLB samples collected from different hosts with different symptoms in seven Chinese provinces, were subjected to PCR for amplifying and sequencing the 16S rDNA. The identity level among Chinese isolates was 98.5% to 100% and was the same with the Indian HLB isolate ‘Poona’ (GenBank accession number: L22532). By contrast, identity values were 97.5% to 97.8% with Candidatus Liberibacter africanus strain ‘Nelspruit’ (L22533), 96.3% to 97.3% with Ca. L. africanus subsp. ‘Capensis’ (AF137368), 95.3% to 96.5% with the Ca. Liberibacter sp. ‘LSg2’ (AY919312), and 94.9% to 96.0% with a strain of Ca. L. americanus from Brazil (São Paulo State; AY742824). A phylogenetic tree constructed with 16S rDNA sequences showed that all Chinese isolates belong to Ca. L. asiaticum. Analysis of the 16S/23S rDNA intergenic region was conducted on 18 HLB-diseased citrus samples with different symptoms, collected in seven provinces. These isolates showed no obvious variation and had an identity level >99.0% with one another. Sequence analysis of 16S/23S rDNA intergenic region and the relative phylogenetic tree showed that the Chinese isolates are very close to Ca. L. asiaticus, and distinct from Ca. L. africanus and Ca. L. americanus. These results suggest that the Chinese HLB isolates belong to the species Candidatus Liberibacter asiaticus. This is the first report on the classification of HLB isolates from China based on molecular investigations.
 
GenBank accession numbers of phytoplasmal 16S rRNA gene sequences used in this study
Analysis of putative restriction sites in cloned DNA sequences from ribosomal RNA operons rrnA and rrnB of dandelion virescence phytoplasma DanVir and of cirsium whiteleaf phytoplasma CirWL. The sequences from DanVir phytoplasma are comprised of most of the 16S rRNA gene, the 16S-23S rRNA spacer region, and the 5-end of the 23S rRNA gene. The sequences from CirWL phytoplasma are 16S rRNA gene sequences. Arrows indicate restriction sites by which operons rrnA and rrnB of each phytoplasma may be distinguished. The solid bar represents the sequence amplified in PCR primed by oligonucleotide pair F2n/R2; phytoplasma classification into 16S rDNA groups and subgroups is based upon restriction sites in this sequence.
Article
Previously undescribed phytoplasmas were detected in diseased plants of dandelion (Taraxacum officinale) exhibiting virescence of flowers, thistle (Cirsium arvense) exhibiting symptoms of white leaf, and a Gaillardia sp. exhibiting symptoms of stunting and phyllody in Lithuania. On the basis of restriction fragment length polymorphism (RFLP) analysis of 16S rDNA amplified in PCR, the dandelion virescence (DanVir), cirsium whiteleaf (CirWL), and gaillardia phyllody (GaiPh) phytoplasmas were classified in phylogenetic group 16SrIII (X-disease phytoplasma group), new subgroups III-P and III-R and subgroup III-B, respectively. RFLP and nucleotide sequence analyses revealed 16S rRNA interoperon sequence heterogeneity in the two rRNA operons, rrnA and rrnB, of both DanVir and CirWL. Results from phylogenetic analysis based on nucleotide sequences of 16S rDNA were consistent with recognition of the two new subgroups as representatives of distinct new lineages within the group 16SrIII phytoplasma subclade. The branching order of rrnA and rrnB sequences in the phylogenetic tree supported this interpretation and indicated recent common ancestry of the two rRNA operons in each of the phytoplasmas exhibiting interoperon heterogeneity.
 
Phytoplasma strains employed in molecular analyses
Phylogenetic tree constructed by the neighbour-joining method of 16S rRNA gene sequences from 28 phytoplasma taxa and employing culturable Acholeplasma palmae as the out group. Bootstrap values are shown on the branch. Ash yellows (ASHY); Almond witches' broom (AWB); Black alder witches' broom (BaWB); Bermuda grass white leaf (BGWL); Brinjal little leaf (BLL); Coconut lethal yellowing (CLY); 'Candidatus Phytoplasma brasiliense' (Pbras); Centaurea solstitialis virescence (CSV); Clover proliferation (CP); Epilobium phyllody phytoplasma (EpP); Elm yellows (EY); European stone fruit yellows (ESFY); Erigeron witches' broom (EWB); Faba bean phyllody (FBP); Flavescence dorée (FD); Fragaria multicipita (FM); Illinois elm yellows (ILEY); Loofah witches' broom (LfWB); Mexican periwinkle virescence (MPV); Picris echioides phyllody (PEP); Picris echioides yellows (PiEP); Peanut witches' broom (PWB); Rice yellows dwarf (RYD); Sugarcane white leaf (SCWL); Stolbur (STOL); Spartium witches' broom (SWB); Tomato big bud (TBB); Walnut witches' broom (WWB). The homology (%), obtained using CLUSTALW program by comparison to CSV 16S and all considered phytoplasma sequences, is reported at the extremities of the corresponding branch.
Article
In the United States, yellow starthistle (Centaurea solstitialis) is an annual invasive weed with Mediterranean origins. Malformed plants displaying witches' broom, fasciations, abortion of buds and flower virescence symptoms were observed in central Italy. Attempts to transmit the causal agent from the natural yellow starthistle host to periwinkle by grafting, resulted in typical symptoms of a phytoplasma, i.e. yellowing and shortening of internodes. The detection of phytoplasmas was obtained from both symptomatic yellow starthistle and periwinkle by the specific amplification of their 16S-23S rRNA genes. PCR amplification of extracted DNA from symptomatic plant samples gave a product of expected size. Asymptomatic plants did not give positive results. An amplicon obtained by direct PCR with universal primers P1/P7 was cloned and sequenced. The homology search using CLUSTALW program showed more than 99% similarity with Illinois elm yellows (ILEY) phytoplasma from Illinois (United States) and 97% with Brinjal little leaf (BLL) phytoplasma from India. Digestion of the nested-PCR products with restriction enzymes led to restriction fragment length polymorphism patterns referable to those described for phytoplasmas belonging to the clover proliferation (16S-VI) group. Since this is a previously undescribed disease, the name Centaurea solstitialis virescence has been tentatively assigned to it. This is a new phytoplasma with closest relationships to ILEY and BLL, but distinguishable from them on the basis of 16S rDNA homology, the different associated plant hosts and their geographical origin.
 
ClustalW alignment of the amino-acid sequences encoded by the ERG27 genes from S. cerevisiae, C. albicans, the B. cinerea putative ERG27 gene and the human 17β-HSD7 gene (http://www2.ebi.ac.uk/clustalw). Shaded areas indicate regions of sequence identity. Similar residues when found at least in the human enzyme and in one of other sequences or alternatively in the three fungal sequences are shown in boldface. Human exons boundaries are indicated by vertical bars, note that the unique B. cinerea exon boundary is located at the same position as the first human one (yeasts ERG27 genes are devoided of intron). NADPH cofactor binding sites, NAGI motif and putative transmembrane domain are underlined. The two residues involved in active site, i.e., Y and K (consensus sequence YXXXK) are indicated by arrowsheads. Primers used in this study are namely indicated by horizontal arrows under the B. cinerea sequence.
Response of the various phenotypes of B. cinerea towards two fungicides: fenhexamid and prochloraz
Primers designed for this study
Erg27p like protein polymorphism among the different B. cinerea Hyd phenotypes (between amino-acid positions 70 and 500). Mutations in the B. cinerea Erg27p like protein sequences are shown in shaded boxes and the corresponding phenotypes are indicated in the left column. The NAGI motif (also found in mammalian 17β-HSD7) and the reductase active site are shown in boxes, the putative transmembrane helix is delimited by arrowheads.
Article
Botrytis cinerea (anamorph of Botryotinia fuckeliana) is a filamentous ascomycete that causes grey mould on grapevine. We had previously described two distinct populations, named HydR1 and non-HydR1, that comprise two distinct genetic entities based on genetic polymorphism, natural resistance towards the fungicide hydroxyanilide fenhexamid, and vegetative incompatibility between them. Here, we used PCR to isolate the 3-keto reductase gene ERG27 by virtue of sequence homology with Saccharomyces cerevisiae ERG27. The gene product was longer than the yeast''s enzyme but possessed the main characteristic features of reductases. It displayed striking homology with mammalian 17-HSD7, therefore confirming the hypothesis of a common function between Erg27p like protein and 17-HSD7 in sterol biosynthesis (i.e. cholesterol, ergosterol). On the other hand, we analysed the polymorphism of the B. cinerea gene product and found a dozen of amino-acid differences between strains of HydR1 and non-HydR1 types that could underlie HydR1 natural resistance to fenhexamid. First, this polymorphism analysis showed that HydR1 strains form a homogeneous group distinct from the non-HydR1 group of strains. These results support our hypothesis that HydR1 and non-HydR1 strains constitute two different species. Second, Erg27p like protein sequence analysis showed that a high resistant phenotype to fenhexamid, HydR3, found in treated populations of non-HydR1 strains, had two mutations (usually found in mammalian 17-HSD7) that could be useful as population markers.
 
Article
From 18 tobacco mosaic virus isolates from tomato, which could be divided into 3 pathogenicity groups, the buoyant density, the S value, the base composition, the amino acid composition, and the behaviour of their tryptic peptides in thin-layer chromatography were compared. There were no differences in buoyant densities and S values. With respect to the other characteristics only small individual differences could be detected. Pathogenicity of the isolates was not correlated with the chemical and physical properties.Van 18 tabaksmozaekvirusisolaten van tomaat, die konden worden onderscheiden in 3 pathogeniteitsgroepen, werden de zweefdichtheid, de sedimentatiecofficint, de basesamenstelling, de aminozuursamenstelling en het gedrag van peptiden van het manteleiwit in dunne-laagchromatografie vergeleken. Er was geen verschil in zweefdichtheid en sedimentatiecofficint. Met betrekking tot de andere kenmerken konden alleen individuele verschillen worden aangetoond. Er kon geen verband worden gevonden tussen de pathogeniteit van de isolaten en hun chemische en fysische eigenschappen.
 
Article
The Tijdschrift over Planteziekten, 1895–1963 (Netherlands Journal of Plant Pathology, 1963 on) was analysed to assess the development of plant pathology in the Netherlands. The approach to phytopathological problems is becoming more and more specialized and field work has given way to experimentation in the laboratory.De publikaties in het Tijdschrift over Planterziekten (Netherlands Journal of Plant Pathology) over de afgelopen tachtig jaar werden vijfjaarlijks geanalyseerd. De geconstateerde tendensen zijn een verschuiving van onderzoek te velde naar onderzoek in het laboratorium, een toenenmende specialisatie binnen het vakgebied en een overgang van observatie naar experimentatie. De resultaten van dit literatuuronderzoek geven duidelijke tendensen aan, maar bieden geen volledig beeld van de Nederlandse planteziektenkunde.
 
Article
Samples of heavily infested crop residues were incorporated in static compost heaps (2.5–4.6 m3) of the Indore type. Temperature increased to 50–70°C within 6 days depending on the type of crop residues used and the location within the heap. The heat phase (>40 °C) lasted 2–3 weeks and was followed by a c. 5-months maturation phase (<40 °C). Among the 17 pathogens tested, onlyOlpidium brassicae and one of the four formae speciales ofFusarium oxysporum that were tested survived composting, but also their inoculum was greatly reduced. Survival during specific phases of composting was studied by incorporation and retrieval of samples at various stages of the process.F. oxysporum f. sp.melonis was completely inactivated andO. brassicae andPlasmodiophora brassicae were almost completely inactivated during the short heat phase. The three pathogens survived the long-lasting maturation phase without loss of viability. Heat evolved during composting was found to be the most important factor involved with sanitation of crop residues. The possible involvement of fungitoxic conversion products and microbial antagonism is discussed.
 
Article
Onderzoekingen zijn gedaan over de omvang, die de loodglansziekte heeft aangenomen bij een aantal pruimenrassen in de Betuwe, gedurende de jaren 1941 tot en met 1946.Het is gebleken, dat de ziekte gedurende die tijd is toegenomen bij Victoria, Early Laxton, Belle de Louvain, Monsieur htif en Eldense Blauwe, en afgenomen bij Doyenn, Reine Claude d'Althann en Jefferson. Bij Reine Claude d'Oullins is de omvang ongeveer gelijk gebleven, bij Czar bereikte de ziekte in 1943 een maximum, en nam daarna weer af.Berekend is, welke kans er bestaat voor de bomen van de verschillende rassen om loodglansziek te worden, en welke kans de aangetaste bomen hebben om weer te genezen.Bij Victoria bleken struiken en hoogstammen in gelijke mate door de ziekte te zijn aangetast.Er is enige aanwijzing dat de loodglansziekte op verschillende percelen niet in gelijke mate optreedt.Investigations have been made on the severity of the silver-leaf disease in a number of varieties of plum grown in the Betuwe during the years 1941 to 1946 (Tab. 1).It appeared that over this period the disease increased in Victoria, Early Laxton, Belle de Louvain, Early Orleans and Early Rivers, and decreased in Doyenn, Reine Claude d'Althann and Jefferson. In Reine Claude d'Oullins the disease remained nearly at the same level. In Czar it reached a very pronounced maximum in 1943 and then decreased (Fig. 1 and 2 and Tab. 2 and 3).The susceptibility of the different varieties has been compared and expressed numerically. Calculations have been made to show what the chances are that the trees of the different varieties will become diseased, and also, what the chances are that the diseased trees will recover (Tab. 4 and 5).Bush-trees and standard trees of the Victoria plum proved to be equally attacked (Tab. 6).There is a certain amount of evidence that the severity of the disease is not the same in all orchards (Tab. 7).The results are important for practical fruit-growing and also for the further investigations on the silver-leaf disease; it is pointed out that recovery after a treatment is only significant in varieties in which very little natural recovery occurs.As it appeared that the severity of the disease may change suddenly, as in Czar, this investigation must be continued.
 
Article
Heterodera cruciferae is found in the Netherlands in five different locations, living on cabbage, rape and rapeseed, whereas beets are not attacked. ThisHeterodera is distinguished from nearly all otherHeterodera's known in Europe by its small, red brown, roundish lemon-shaped cysts and its short, thick larvae (Fig. 1, 2, 3, 5). The only exception isHeterodera humuli, which has however a thinner cyst wall of a lighter colour with a conspicuous, coarse, irregular punctation and larva stylets with distinctly forward-pointing knobs (Fig. 7, 8). The males are redescribed; they have 5–7 lip annules and three teeth on each spiculum tip (Fig. 4). Population density and type of damage with culture of rape seem to be about the same as with beet sickness caused byH. schachtii (Fig. 6). In the most important cabbage areaH. schachtii plays a more important role thanH. cruciferae. With both eelworms, an advisory service based on soil sample examinations would probably be useful for the culture of cruciferous crops.
 
Article
Op vele bedrijven, waar een sterke rotatie van granen in het bouwplan is opgenomen, kan het havercystenaaltjes veelvuldig moeheidsverschijnselen in haver veroorzaken. Ook op bedrijven, waar dit gewas geen afwijkingen in de groei vertoont, komt het aaltje, zij het in geringe concentraties, algemeen voor. Tussen de besmettingsgraad van de grond en de schade aan het gewas bestaat een zeker verband. Dit verbank kan sterk beïnvloed worden door verschillende bijkomende factoren, waaronder de watervoorziening van der planten een belangrijke rol speelt. Het is nog niet duidelijk in hoeverre de techniek van het grondmonsteronderzoek gewijzigd dient te worden om te voorkomen, dat de levende inhoud van de cysten terugloopt.
 
Article
Observations on the occurrence of diseases of pea,Pisum sativum, in five European countries in 1957 are reported. Areas visited, numbers of fields studied, and appropriate dates are indicated. The pea diseases found, together with estimates of the amount of infection by each are given. No accuracy of relative economic importance of the diseases is claimed but significance is attached to the finding of certain pea diseases for the first time in several of the countries visited. In 1957 bezocht de schrijver erwtevelden in Nederland, Zwitserland, West-Duitsland, Engeland en Zweden en noteerde de mate, waarin de desbetreffende gewassen door een aantal ziekten waren aangetast. In de waarnemingen waren de volgende ziekten betrokken: bacterieziekte, vlekkenziekte, Amerikaanse vaatziekte, Fusarium wortelrot, valse meeldauw, „enation”-mozaïek, mozaïek, strepenziekte („streak”), dwergziekte („stunt”), topvergeling, aaltjes en waterophoping in de intercellulairen („water congestion”). De mate van aantasting werd geschat en als volgt uitgedrukt: spoor, minder dan 1% van de planten ziek; licht, 1–4% aantasting; matig, 5–10% aantasting; sterk, 11–25% aantasting; zeer sterk, meer dan 25% aangetast. Tabel 1 geeft een overzicht van deze waarnemingen. Enige ziekten werden in sommige landen voor de eerste keer gevonden. Het betreft in Nederland de dwergziekte, waarvan het virus ook in klaver werd aangetroffen; in Zwitserland „enation”-mozaïek, mozaïek, strepenziekte, dwergziekte, topvergeling en waterophoping in de intercellulairen; in Engeland dwergziekte en topvergeling; in Zweden „enation”-mozaïek, mozaïek, strepenziekte, dwergziekte en ophoping van water in de intercellulairen.
 
Article
Some observations have been made on lucerne wilt disease during the growing season in 1957, and in experimental inoculation tests in a glasshouse in 1958. In the province of Zeeland the disease does harm to the crop and prevents many farmers from keeping their crops longer than two years.In a survey data have been collected on soil type, preceding crops, green manuring and manuring with stable dung, pH, structure and weeds. No correlations between these factors and the degree of attack by the disease could be proved, except that on heavy soils the disease was less severe than on lighter soils (as a mean of all observations).Development of the disease is facilitated by damage caused by mechanical equipment to the crop. Damage to the crown of the plants should be avoided as much as possible. The disease is distributed extensively after frequent mowing. On attacked leaves left behind on the mowed stalks, and on decayed leaves dropped to the soil, masses of spores ofVerticillium albo-atrum are produced, which form a potential source of infection in a weakened crop.It seems that the disease is more air-borne than soil-borne, since one year old crops are seldom attacked.From attacked lucerne plants in the field the following fungi have been isolated:Verticillium albo-atrum Reinke & Berth.,Gliocladium roseum Bain andFusarium avenaceum (Fr.) Sacc. (table 1).Isolations have been made from 50 different species of weeds, out of which the following fungi were obtained:Verticillium albo-atrum Reinke & Berth. fromCapsella bursa-pastoris Med. andPlantago major L.,V. dahliae Kleb. fromPrunella vulgaris L.,Capsella bursa-pastoris Med. andThlaspi arvense L., andV. lecanii (Zimm.) Viegas fromPlantago major L.In inoculation experiments with all these isolates, in roots, stalks and on cut plants of lucerne, onlyV. albo-atrum, both from lucerne and weeds, andV. lecanii proved to be able to cause wilting of leaves and stalks. WithGliocladium, Fusarium andVerticillium dahliae no such symptoms could be obtained. The results were the same whatever method of inoculation was used.
 
Article
Een beschrijving wordt gegeven van de levenswijze van de groene, rode of gele bladluisMasonaphis lambersi, die in Nederland en Engeland bladhoudende en bladverliezende, buitengroeiende rhododendrons aantast. Aan aangetaste scheuten van bladhoudendeRododendron ponticum hybriden blijven den bladen klein, en er worden geen bloemknoppen aangelegd. Vervellingshuidjes en dode luizen blijven meestal maandenlang aan dedaardoor grijsgroene bladeren vastkleven.R. molle hybriden vertonen bij ernstige aantasting onregelmatig gewelfd blad en verdrogingsverschijnselen, maar maken normaal bloemknoppen.R. ferrugineum andR. praecos werden niet aangetast. De bladluis was slechts uit de Westelijke kuststaten van de Verenigde Staten bekend, en werd, na signalering vanuit Nederland, ook in Engeland gevonden. De kleverige jonge scheuten en bladeren vanR. ponticum hybriden werken als lijmstokken voor bladluisparasieten en ook voor andere bladluissoorten. Inhemse roofvjanden worden op eendere wijze in hun verplaatsing belemmered. Op bladverliezende rhododendron vond evenmin parasitering en nagenoeg geen predatie plaats. Invoer van eventuele, aangepaste natuurlijke vijanden uit Ameika wordt wenselijk geacht. Op bladhoudende rhododendrons zou bestrijding gewenst kunnen zijn, mar de schade valt pas op als de luizen door verouderen van het blad uitsterven. De overwintering op bladhoudende vormen lijkt uitgesloten.
 
Article
Johan Dekker, born 26 november 1925, in's Heerenhoek (on the island Zuid Beveland in the southwest of the Netherlands), grew up in a rural environment and was initiated in all farming practices. He went to grammar school (gymnasium β) during the turbulent years of the Second World War and graduated in 1945. He continued his education at the Wageningen Agricultural University, where he chose Tropical Agronomy as a major and Phytopathology as a minor. The academic studies were interrupted to do military service (1947-1950; reserve officer), which in the unstable post-war period required many years. The then mature student apparently became fascinated with phytopathology, as testifies his undergraduate thesis on Rhabdospora ramealis (purple blotch, now R. ruborum) as the causal agent of a blueberry disease, but he did not forget about his major, vide the literature review on rubber mildew (Oidium heveae) which would have fit in the Annual Review of Phytopathology as to thoroughness and number of references. Did his student work already indicate Dekker's abilities as an editor and review writer? © 1989 Koninklijke Nederlandse Planteziektenkundige Vereniging.
 
Article
The plant–parasitic nematode Longidorus poessneckensis from the Czech Republic was morphologically and molecularly characterised. Molecular analyses were carried out using mitochondrial DNA (cytochrome c oxidase subunit 1—cox1) and ribosomal DNA (ITS2—second internal transcribed spacer, 18S gene and D2/D3 expansion segments of the 28S gene), which were amplified and sequenced. Phylogenetic relationship of L. poessneckensis with three morphologically closely related species, i.e. L. macrosoma, L. helveticus and L. uroshis, was inferred by using maximum likelihood and maximum parsimony methods, with a female of Xiphinema diversicaudatum and a bivulval female of X. vuittenezi as outgroups. All multiple alignments yielded similar basic trees supporting the uniqueness of L. poessneckensis and the validity of the four Longidorus species identified using morphological characters. Phylogenetic analyses revealed that L. poessneckensis is more closely related to L. macrosoma and L. helveticus than to L. uroshis. High inter-population diversity (19%) was observed across the cox1 gene between two populations of L. poessneckensis.
 
Article
During 1974–86, systematic annual surveys of diseases and pests in winter wheat were conducted. In a series of papers the occurrence of diseases and pests will be reported in relation to weather and cropping practices. In this paper, an introduction to the series of papers, the weather and the the changing winter wheat cropping practices are described. Grain yields and pesticide use in the surveyed fields are reported.Wintertarwe werd systematisch genventariseerd op ziekten en plagen in de jaren 1974–86. In een serie artikelen zal het optreden van ziekten en plagen worden besproken in relatie tot het weer en cultuurmaatregelen. Dit artikel is daarop een inleiding. Het jaarlijkse weer werd gekarakteriseerd door de gemiddelde maandtemperaturen en de totale hoeveelheid neerslag in een maand. De teelt van wintertarwe gedurende 1974–86 wordt kort besproken. De behaalde opbrengsten en het gebruik van chemische bestrijdingsmiddelen in de genventariseerde percelen wordt gerapporteerd.
 
Article
Mildew epidemics in 1980 on winter wheat cv. Sadovo 1 near Sofia, Bulgaria, were studied in detail. Half of the experimental plots were artificially inoculated, whereas the others were naturally infected. Fungicide treatments on all plots consisted of from nil to three applications of triadimefon. On four days, mildew severity, plant height and the yield components ear length, number of kernels, and grain weight per ear were determined. Mildew incidence showed to be a simple and reliable predictor of yield loss. It is suggested that mildew incidence can be used for decision making in the supervised control of wheat mildew in Bulgaria.Sofia, Bulgarije, in detail bestudeerd. Van 32 veldjes van 1 m2 groot, in vier blokken van acht veldjes verdeeld over een groot tarweperceel, werd de helft kunstmatig genfecteerd met meeldauw, terwijl de andere helft aan natuurlijke infectie werd blootgesteld. De bespuitingen varierden van een tot drie bespuitingen met triadimenfon, alsmede een onbespoten controle. Op drie dagen werden aantastingsgraad en incidentie van meeldauw bepaald aan de drie bovenste bladlagen. Een aantal relaties werd berekend tussen incidentie, aantastingsgraad en opbrengstvariabelen (planthoogte, aarlengte, aantal korrels per aar, korrelgewicht per aar). In ontwikkelingsstadium F 10.1 bleek meeldauw-incidentie een eenvoudige en betrouwbare maat te zijn voor toekomstige opbrengstderving. Meeldauw-incidentie kan als maat gebruikt worden bij de geleide bestrijding van meeldauw in Bulgarije, maar er zullen nog veel proeven nodig zijn om dit doel te bereiken.
 
Article
Cereal aphids on a wheat crop were sampled through the winter of 1982/1983 using both fixed and random quadrats.Sitobion avenae overwintered successfully anholocyclically although there was a substantial decline in the population of this species. No evidence for successful anholocyclic overwintering in other aphid species was found, althoughRhopalosiphum padi was seen to colonise the crop in early winter and was found until the end of December. Eggs ofR. padi onPrunus padus were observed through the winter. A steady decline in their numbers occurred. The overall survival rate of the 5385 eggs was c.30%. Eggs ofMetopolophium dirhodum onRosa spp. were also monitored. They also showed a steady decline in numbers through the winter. The overall survival rate of the 1360 eggs was c.34%. Egg hatch in bothR. padi andM. dirhodum was closely synchronised with bud burst of their host plant. For the latter species this resulted in egg hatch starting in January.
 
Article
Ninety-five isolates ofPhytophthora infestans collected throughout Poland during 1985–1991 and characterized for multilocus genotypes based on mating type, allozymes and DNA fingerprint, were analyzed for specific virulence to differential potato cultivars carrying ten major resistance genes. The multilocus analysis led to three groupings. The first group contained 22 isolates of a clonal lineage (PO-1) that is postulated to have been present in Europe during most of the twentieth century, but PO-1 isolates were recovered in Poland only during 1985–1988. This group contained, on average, virulence to 5.5 specific resistance genes per isolate. The second group consisted of 30 isolates in a clonal lineage (PO-4) that had not been detected before 1988. PO-4 isolates had virulence to a mean of 6.5 resistance genes per isolate. The third group was composed of 43 isolates representing 38 multilocus genotypes also not detected before 1988. These diverse genotypes had virulence to an average of 6.7 specific resistance genes per isolate. More than half (53%) of the PO-4 isolates shared a single pathotype. The group of 43 isolates was dominated by two pathotypes: the most common one (47% of the isolates) was the same pathotype that dominated PO-4 isolates; the next most common one (21%) differed from the most common one by the absence of virulence to resistance gene R5. The recent immigrant isolates (not detected before 1988) generally had virulence to a greater number of specific resistance genes than did isolates in the previous population [detected before 1988 (PO-1)]. Recent immigrant populations were dominated by one or two pathotypes, so their pathotypic diversity values were somewhat less than that of the previous population.
 
Article
In 1993–1996, the virulence of regional populations of the wheat powdery mildew pathogen (Erysiphe graminis DC f. sp. tritici Marchal) from the Czech Republic, Austria, Hungary and Slovakia against 13 resistance genes was investigated. The populations differed mainly at the regional level. Populations from the Czech Republic, mainly from the western regions, showed higher values of virulence against the Pm4b gene. Lower frequency of virulence against Pm4b was found in Austria, and the lowest value was observed in Hungary. The differences in frequencies of virulence against Pm4a and Pm4b showed a similar geographic pattern across the four countries: a continuous decline from west to east and from north to south. Virulence against Pm2 decreased in all countries considered; virulence to pm5, Pm6, Pm8 and Mli was high throughout. Genes and gene combinations that can ensure a relatively effective biological protection against this pathogen across Central Europe at present are Pm3b, Pm2+Mld and Pm1+2+9. Czech and Slovak populations were the most complex: virulence complexity reached a maximum in Slovakia in 1994. A similar evolution, though less significant, was observed in the Czech Republic. Data on complexity of isolates suggest that Central European populations of wheat powdery mildew tend to reach an intermediate level representing the optimal number of virulence genes. This process is probably a consequence of stabilizing selection.
 
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Aziz Aziz
  • Université de Reims Champagne-Ardenne
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  • Université de Reims Champagne-Ardenne
Carla Nunes
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Michel Couderchet
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Sami Michereff
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