Strobilurins are one of the most important classes of agricultural fungicide. Their invention was inspired by a group of fungicidally active natural products. The outstanding benefits they deliver are currently being utilised in a wide range of crops throughout the world. First launched in 1996, the strobilurins now include the world's biggest selling fungicide, azoxystrobin. By 2002 there will be six strobilurin active ingredients commercially available for agricultural use. This review describes in detail the properties of these active ingredients--their synthesis, biochemical mode of action, biokinetics, fungicidal activity, yield and quality benefits, resistance risk and human and environmental safety. It also describes the clear technical differences that exist between these active ingredients, particularly in the areas of fungicidal activity and biokinetics.

The strobilurin fungicides.

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Myths and Dogmas of Biocontrol Changes in Perceptions Derived from Research on Trichoderma harzinum T-22.

Wine grapes present a unique biogeography model, wherein microbial biodiversity patterns across viticultural zones not only answer questions of dispersal and community maintenance, they are also an inherent component of the quality, consumer acceptance, and economic appreciation of a culturally important food product. On their journey from the vineyard to the wine bottle, grapes are transformed to wine through microbial activity, with indisputable consequences for wine quality parameters. Wine grapes harbor a wide range of microbes originating from the surrounding environment, many of which are recognized for their role in grapevine health and wine quality. However, determinants of regional wine characteristics have not been identified, but are frequently assumed to stem from viticultural or geological factors alone. This study used a high-throughput, short-amplicon sequencing approach to demonstrate that regional, site-specific, and grape-variety factors shape the fungal and bacterial consortia inhabiting wine-grape surfaces. Furthermore, these microbial assemblages are correlated to specific climatic features, suggesting a link between vineyard environmental conditions and microbial inhabitation patterns. Taken together, these factors shape the unique microbial inputs to regional wine fermentations, posing the existence of nonrandom “microbial terroir” as a determining factor in regional variation among wine grapes.

https://www.pnas.org/content/pnas/111/1/E139.full.pdf

Microbial biogeography of wine grapes is conditioned by cultivar, vintage, and climate

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.

/pdf/the-top-10-oomycete-pathogens-in-molecular-plant-pathology-3gxpkolrjj.pdf

The Top 10 oomycete pathogens in molecular plant pathology

The microbial ecology of wine grape berries.

Austin, C. N., and Wilcox, W. F. 2012. Effects of sunlight exposure on grapevine powdery mildew development. Phytopathology 102:857-866. Natural and artificially induced shade increased grapevine powdery mildew (Erysiphe necator) severity in the vineyard, with foliar disease severity 49 to 75% higher relative to leaves in full sun, depending on the level of natural shading experienced and the individual experiment. Cluster disease severities increased by 20 to 40% relative to those on check vines when ultraviolet (UV) radiation was filtered from sunlight reaching vines in artificial shading experiments. Surface temperatures of leaves in full sunlight averaged 5 to 8°C higher than those in natural shade, and in one experiment, filtering 80% of all wavelengths of solar radiation, including longer wavelengths responsible for heating irradiated tissues, increased disease more than filtering UV alone. In controlled environment experiments, UV-B radiation reduced germination of E. necator conidia and inhibited both colony establishment (hyphal formation and elongation) and maturity (latent period). Inhibitory effects of UV-B radiation were significantly greater at 30°C than at 20 or 25°C. Thus, sunlight appears to inhibit powdery mildew development through at least two mechanisms, i.e., (i) UV radiation’s damaging effects on exposed conidia and thalli of the pathogen; and (ii) elevating temperatures of irradiated tissues to a level supraoptimal or inhibitory for pathogen development. Furthermore, these effects are synergistic at temperatures near the upper threshold for disease development.

https://apsjournals.apsnet.org/doi/pdf/10.1094/PHYTO-07-11-0205

Effects of Sunlight Exposure on Grapevine Powdery Mildew Development

Black-foot disease of grapevine is caused by a complex of soilborne fungi. The most common and virulent species, which are found across all major grapegrowing regions of the world, are Cylindrocarpon liriodendri (C. liriodendri) and C. macrodidymum (teleomorph = Neonectria). Other species with a more limited distribution and uncertainty regarding their pathogenicity include C. destructans, C. obtusisporum, C. pauciseptatum, Campylocarpon fasciculare (C. fasciculare), and C. pseudofasciculare. The goal was to identify the species associated with black-foot disease in vineyards of the northeastern United States (U.S.) and southeastern Canada as such regions have not previously been surveyed. Recent expansion of winegrape acreage in these regions necessitates a clear understanding of the disease risks. Eleven U.S. states and two Canadian provinces were surveyed. Genus-level identification was based preliminarily on colony morphology. Species-level identity was based on phylogenetic analysis of two nuclear loci, 5.8S rDNA and s-tubulin, using voucher specimens and sequences with high sequence identity. We report for the first time from Canada recovery of C. liriodendri, C. macrodidymum, and C. destructans from symptomatic grapevines. Also reported are species not previously identified from black-foot symptomatic grapes anywhere in the world, including C. didymum and a Neonectria mammoidea-like species. Results suggest that local viticultural practices, primarily burying the vine underground during winter, may create injuries, and thus exacerbate infection by wound pathogens such as Cylindrocarpon. Overall this work improves the knowledge of black-foot disease in these nascent grapegrowing regions and will be helpful to growers in their decisions regarding viticultural practices, planting, and disease management.

Cylindrocarpon Species Associated with Black-Foot of Grapevine in Northeastern United States and Southeastern Canada

Gadoury, D. M., Seem, R. C., Ficke, A., and Wilcox, W. F. 2001. The epidemiology of powdery mildew on Concord grapes. Phytopathology 91:948-955. Vitis labruscana ‘Concord’ is a grape cultivar widely grown in the United States for processing into juice and other grape products. Concord grapes are sporadically but sometimes severely damaged by the grape powdery mildew pathogen, Uncinula necator. Although the foliage is often reported to be moderately resistant to powdery mildew, severe fruit infection occurs in some years. We observed the seasonal development of powdery mildew on leaves, rachises, and berries of unsprayed Concord grapevines. Inoculations of flower and fruit clusters revealed a brief period of berry susceptibility and a protracted period of rachis susceptibility. The rachis remained highly susceptible to infection, and the severity of rachis infection increased throughout the growing season until the rachis formed a periderm shortly before harvest. In contrast, berries were nearly immune to infection within 2 weeks after fruit set. Rachis and berry infections were detected before the disease was observed on foliage, and the incidence of rachis and berry infection often exceeded disease incidence observed on foliage until after fruit acquired substantial ontogenic resistance. Excellent control of fruit infection, and adequate control of leaf infection, was achieved by two fungicide applications targeted at the peak period of fruit susceptibility. Although Concord is thought to be moderately resistant to powdery mildew, the rachis is highly susceptible, and may be the avenue by which prebloom infections make their way onto the developing fruit. Late-season infection of the rachis neither spread to the fruit, nor did it cause fruit to drop prematurely, and may be of little economic consequence on fruit destined for processing. Although fruit of V. vinifera cultivars have been reported to remain susceptible to infection until berry sugar levels reach 8 to 15%, Concord fruit become nearly immune to infection nearly 6 weeks before this stage of development. Because powdery mildew does not become conspicuous on foliage until late summer, it is generally regarded as a late-season problem on Concord grapes, and previous management programs have reflected this belief. However, the greatest contribution to control of fruit infection is due to fungicides applied during the peak period of fruit susceptibility, from bloom until shortly after fruit set, long before the disease is observed on foliage.

https://apsjournals.apsnet.org/doi/pdfplus/10.1094/PHYTO.2001.91.10.948

The epidemiology of powdery mildew on concord grapes.

Apple scab (Venturia inaequalis) is a perennial threat to apple production in temperate climates throughout the world. In the eastern United States, apple scab is managed almost exclusively through the regular application of fungicides. Management of the primary phase of disease is focused on preventing infection by ascospores. Management of secondary cycles of infection is largely dependent on how well primary infections were controlled. In this study, we used receiver operating characteristic curve analysis to evaluate how well mid-season assessments of the incidence of apple scab on cluster leaves, clusters (i.e., the whorl of cluster leaves), or immature fruit can serve as predictors of apple scab on harvested fruit (harvest scab) and whether these mid-season assessments of scab could be used reliably to manage scab under various damage thresholds. Results showed that assessment of scab on immature fruit was superior at predicting harvest scab than were assessments made on clusters or cluster leaves at all damage thresholds evaluated. A management action threshold of 7% scab incidence on immature fruit was identified by Youden's index as the optimal action threshold to prevent harvest scab incidence from exceeding 5%. Action thresholds could be higher or lower than 7% when economic assumptions were factored in to the decision process. The utility of such a predictor is discussed.

https://apsjournals.apsnet.org/doi/pdf/10.1094/PHYTO-95-0679

Evaluating Predictors of Apple Scab with Receiver Operating Characteristic Curve Analysis

Cytospora species are ubiquitous pathogens of numerous woody plants, causing dieback and wood cankers in agronomic crops, timber trees, and wildland trees (e.g., Prunus, Eucalyptus, and Salix, respectively). Cytospora chrysosperma, C. cincta, and C. leucostoma have been reported from grapevines in Iran showing symptoms of one or more recognized trunk diseases (Esca, Botryosphaeria-, Eutypa-, and Phomopsis diebacks); however, only C. chrysosperma was shown to be pathogenic to grapevine. To understand the potential role of Cytospora species in the grapevine trunk-disease complex, we examined 21 Cytospora isolates that were recovered from dieback and wood cankers of Vitis vinifera and Vitis interspecific hybrids in seven northeastern U.S. states and two Canadian provinces. Phylogenetic analyses of ITS and translation elongation factor 1-α identified two novel species: Cytospora vinacea sp. nov. and Cytospora viticola sp. nov. Differences in culture morphology and conidial dimensions also distinguished the species. When inoculated to the woody stems of potted V. vinifera ‘Thompson Seedless’ in the greenhouse, both species were pathogenic, based on development of wood lesions and thus fulfillment of Koch's postulates. Cytospora viticola was the most virulent based on lesion length at 12 months post-inoculation. As Cytospora canker shares some of the same general dieback-type symptoms as Botryosphaeria-, Eutypa-, and Phomopsis diebacks, it may be considered part of the grapevine trunk-disease complex in eastern North America.

This article is protected by copyright. All rights reserved.

https://bsppjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/ppa.12621

Wayne F. Wilcox

Papers

Effects of Sunlight Exposure on Grapevine Powdery Mildew Development

Cylindrocarpon Species Associated with Black-Foot of Grapevine in Northeastern United States and Southeastern Canada

The epidemiology of powdery mildew on concord grapes.

Evaluating Predictors of Apple Scab with Receiver Operating Characteristic Curve Analysis

Characterization of Cytospora isolates from wood cankers of declining grapevine in North America, with the descriptions of two new Cytospora species