Oomycetes form a deep lineage of eukaryotic organisms that includes a large number of plant pathogens which threaten natural and managed ecosystems. We undertook a survey to query the community for their ranking of plant-pathogenic oomycete species based on scientific and economic importance. In total, we received 263 votes from 62 scientists in 15 countries for a total of 33 species. The Top 10 species and their ranking are: (1) Phytophthora infestans; (2, tied) Hyaloperonospora arabidopsidis; (2, tied) Phytophthora ramorum; (4) Phytophthora sojae; (5) Phytophthora capsici; (6) Plasmopara viticola; (7) Phytophthora cinnamomi; (8, tied) Phytophthora parasitica; (8, tied) Pythium ultimum; and (10) Albugo candida. This article provides an introduction to these 10 taxa and a snapshot of current research. We hope that the list will serve as a benchmark for future trends in oomycete research.

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The Top 10 oomycete pathogens in molecular plant pathology

An Improved Grading System For Measuring Plant Diseases Vol-36

In mammals, cadmium is widely considered as a non-genotoxic carcinogen acting through a methylation-dependent epigenetic mechanism. Here, the effects of Cd treatment on the DNA methylation patten are examined together with its effect on chromatin reconfiguration in Posidonia oceanica. DNA methylation level and pattern were analysed in actively growing organs, under short- (6 h) and long- (2 d or 4 d) term and low (10 mM) and high (50 mM) doses of Cd, through a Methylation-Sensitive Amplification Polymorphism technique and an immunocytological approach, respectively. The expression of one member of the CHROMOMETHYLASE (CMT) family, a DNA methyltransferase, was also assessed by qRT-PCR. Nuclear chromatin ultrastructure was investigated by transmission electron microscopy. Cd treatment induced a DNA hypermethylation, as well as an up-regulation of CMT, indicating that de novo methylation did indeed occur. Moreover, a high dose of Cd led to a progressive heterochromatinization of interphase nuclei and apoptotic figures were also observed after long-term treatment. The data demonstrate that Cd perturbs the DNA methylation status through the involvement of a specific methyltransferase. Such changes are linked to nuclear chromatin reconfiguration likely to establish a new balance of expressed/repressed chromatin. Overall, the data show an epigenetic basis to the mechanism underlying Cd toxicity in plants.

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In Posidonia oceanica cadmium induces changes in DNA methylation and chromatin patterning

Normal 0 14 false false false IT ZH-TW X-NONE MicrosoftInternetExplorer4 The oomycete Plasmopara viticola is native to North America and was accidentally introduced into Europe at the end of the 19th century, where it caused widespread damage to the grape industry. Since that time, the damage caused by this plant pathogen has generally been controlled with multiple fungicide applications. Modern fungicides applied as prescribed by weather-based warning systems can effectively prevent any damage that might be caused. Alternatives to chemical treatments, such as the use of biocontrol agents or resistant cultivars, currently play a marginal role in controlling this disease. Until the middle of last century, research efforts were mainly concentrated on optimizing the application of copper fungicides and developing new molecules and formulations for controlling the disease. During the second half of the last century, highly efficient products for control were available, so research efforts moved toward optimizing and minimizing chemical control, mostly through the use of weather-based warning systems based on complex biological models. In the last 20 years, parallel to the development of technologies for genomic and transcriptomic analyses, host-pathogen interactions and population genetics have captured the interest of researchers in this field. Breeding for resistance against downy mildew has always coexisted with chemical control. However, the results of these breeding programmes have traditionally been cultivated only in marginal areas and organic production systems. This review traces the history of European knowledge of P. viticola .

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Plasmopara viticola: a review of knowledge on downy mildew of grapevine and effective disease management

Arthropod-resistant crops provide significant ecological and economic benefits to global agriculture. Incompatible interactions involving resistant plants and avirulent pest arthropods are mediated by constitutively produced and arthropod-induced plant proteins and defense allelochemicals synthesized by resistance gene products. Cloning and molecular mapping have identified the Mi-1.2 and Vat arthropod resistance genes as CC-NBS-LRR (coiled coil-nucleotide binding site-leucine rich repeat) subfamily NBS-LRR resistance proteins, as well as several resistance gene analogs. Genetic linkage mapping has identified more than 100 plant resistance gene loci and linked molecular markers used in cultivar development. Rice and sorghum arthropod-resistant cultivars and, to a lesser extent, raspberry and wheat cultivars are components of integrated pest management (IPM) programs in Asia, Australia, Europe, and North America. Nevertheless, arthropod resistance in most food and fiber crops has not been integrated due primarily to the application of synthetic insecticides. Plant and arthropod genomics provide many opportunities to more efficiently develop arthropod-resistant plants, but integration of resistant cultivars into IPM programs will succeed only through interdisciplinary collaboration.

Molecular Bases of Plant Resistance to Arthropods

To quantify the magnitude and the spatial spread of grapevine downy mildew secondary sporangia, 4685 Plasmopara viticola single lesion samples were collected from 18 plots spread across central Europe. Disease symptoms were collected on two to 22 sampling dates per plot between 2000 and 2002. Four multiallelic microsatellite markers were used for genotypic identification of pathogen samples. Genetic analysis showed more than 2300 site-specific P. viticola genotypes, indicating that populations are genetically rich demographic units. Approximately 70% of the genotypes were sampled once and 14% were sampled twice throughout the various epidemics. In the 18 populations only seven genotypes (0.3%) were identified more than 50 times. Three genotypes particularly successful in causing disease through secondary cycles showed mainly a clustered distribution. The distance of sporangial migration per secondary cycle was less than 20 m and their plot colonization rate was calculated at around 1–2 m2 day−1. Downy mildew epidemics of grapevine are therefore the result of the interaction of a multitude of genotypes, each causing limited (or a few) lesions, and of a dominant genotype able to spread stepwise at plot-scale. These findings contrast with current theories about grapevine downy mildew epidemiology, which postulate that there is massive vineyard colonization by one genotype and long-distance migration of sporangia.

Importance of secondary inoculum of Plasmopara viticola to epidemics of grapevine downy mildew

In view of the ongoing revival of the chestnut orchards in southern Switzerland, evaluation of chestnut quality represents an important issue. Chestnuts are mainly consumed roasted. Three native varieties and a French one were roasted and submitted to sensory and chemical analysis in comparison to a commercial marrone variety imported from Italy. Weight loss due to roasting ranged from 23 to 30%. Roasted chestnuts contained 260-350 g kg -1 starch, 50-102 g kg -1 sucrose, 0.5-4.4 g kg -1 fructose, trace amounts of glucose and 9-15 g kg 1 total fatty acids. The main fatty acid in chestnuts was linoleic acid, amounting to 49% of total fatty acids. Sensory analysis showed that acceptance of chestnuts was highly dependent on sweetness, which was related to sucrose content. It should be at least 90 g kg -1 , Varietal differences were observed in this study and it was shown that roasting caused little change in composition. Thus chestnut varieties used for roasting have to be selected accordingly. The commercial variety Marrone di Cuneo confirmed its superiority with regard to suitability for roasting. Among the Swiss varieties, only Luina exhibited satisfactory quality. Les chataignes sont surtout consommees grillees. Des varietes natives suisses, 1 variete cultivee en France, et 1 variete italienne commerciale sont comparees: L'acide linoleique est l'acide gras principal (49%), la chataigne chaude contient de l'amidon, du saccharose, du fructose et des traces de glucose. Les analyses sensorielles montrent que l'acceptabilite du produit depend surtout de son gout sucre et donc de la teneur en saccharose. C'est la variete commerciale italienne qui presente la meilleure qualite apres grillage.

Effects of roasting on chemical composition and quality of different chestnut (Castanea sativa Mill) varieties

Southern Switzerland has a long tradition of chestnut cultivation as a staple food. Local inhabitants constantly selected varieties according to the ripening period, the type of use, and the adapta...

Microsatellite-based characterization of the Castanea sativa cultivar heritage of southern Switzerland.

With a view to enhancing the quality of local chestnut in southern Switzerland, the impact of three treatments [‘soaking’, ‘cold bath’ (hydrotherapy) and ‘warm bath’ (thermo-hydrotherapy)] on the qualitative, chemical and sensory characteristics of the nuts during 90 days of cold storage was evaluated. Weight and water content decreased significantly with increasing duration of storage. Starch content decreased following a negative logistic trend. Sucrose, however, increased steeply according to a monomolecular trend and was significantly higher between 0 and 60 days of storage in the soaked chestnuts than in the cold-bath treated nuts. The mean proportion of mouldy fruit remained constant at 27% for the warm-bath treated nuts and increased from 16 to 30% for the cold-bath treated fruit and from 28 to 63% for the soaked nuts during the 90 days of cold storage. The most frequently isolated moulds were Ciboria batschiana, Penicillium spp. and Mucor hiemalis. Warm and cold baths were successful in eliminating the larvae of Cydia splendana but the cold bath was inadequate to control Curculio elephas. Cold bath significantly reduced the sensory qualities (sweetness, aroma, texture) of the nuts, but made them easier to peel, as did the warm bath. Copyright © 2006 Society of Chemical Industry

Influence of Fruit Treatments on Perishability During Cold Storage of Sweet Chestnuts

The rosy apple aphid (Dysaphis plantaginea), the leaf-curling aphid (Dysaphis cf. devecta) and the green apple aphid (Aphis pomi) are widespread pest insects that reduce growth of leaves, fruits and shoots in apple (Malus × domestica). Aphid control in apple orchards is generally achieved by insecticides, but alternative management options like growing resistant cultivars are needed for a more sustainable integrated pest management (IPM). A linkage map available for a segregating F1-cross of the apple cultivars 'Fiesta' and 'Discovery' was used to investigate the genetic basis of resistance to aphids. Aphid infestation and plant growth characteristics were repeatedly assessed for the same 160 apple genotypes in three different environments and 2 consecutive years. We identified amplified fragment length polymorphism (AFLP) markers linked to quantitative trait loci (QTLs) for resistance to D. plantaginea ('Fiesta' linkage group 17, locus 57.7, marker E33M35-0269; heritability: 28.3%), and to D. cf. devecta ('Fiesta' linkage group 7, locus 4.5, marker E32M39-0195; heritability: 50.2%). Interactions between aphid species, differences in climatic conditions and the spatial distribu- tion of aphid infestation were identified as possible factors impeding the detection of QTLs. A pedigree analysis of simple sequence repeat (SSR) marker alleles closely associated with the QTL markers revealed the presence of the alleles in other apple cultivars with reported aphid resistance ('Wagener', 'Cox's Orange Pippin'), highlighting the genetic basis and also the potential for gene pyramiding of aphid resistance in apple. Finally, significant QTLs for shoot length and stem diameter were identified, while there was no relationship between aphid resistance and plant trait QTLs.

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Mauro Jermini

Papers

Importance of secondary inoculum of Plasmopara viticola to epidemics of grapevine downy mildew

Effects of roasting on chemical composition and quality of different chestnut (Castanea sativa Mill) varieties

Microsatellite-based characterization of the Castanea sativa cultivar heritage of southern Switzerland.

Influence of Fruit Treatments on Perishability During Cold Storage of Sweet Chestnuts

QTL analysis for aphid resistance and growth traits in apple