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Ceratocystis fimbriata, the causal agent of sweetpotato black rot, is a pathogen capable of developing and spreading within postharvest settings. A survey of North Carolina sweetpotato storage facilities was conducted to determine the arthropods present and identify potential vectors of C. fimbriata. Sixteen taxonomic categories were recovered, and the genus Drosophila (Diptera: Drosophilidae) accounted for 79% of individuals sampled, with Drosophila hydei being the most abundant species. Behavioral assays were conducted to determine if D. hydei is attracted to C. fimbriata-inoculated roots and if the pathogen could be recovered from external or internal surfaces of the insect. Flies were released in insect-trapping pitchers containing either C. fimbriata-inoculated or noninoculated roots or Petri dishes. No significant differences in fly number were detected in sweetpotato-baited pitchers; however, significant differences were found in the pitcher baited with a mature C. fimbriata culture. Flies were subjected to washes to determine if viable C. fimbriata was present (internally or externally); washes were plated onto carrot agar plates and observed for the presence of C. fimbriata colonies. Both external and internal washes had viable C. fimbriata inocula with no significant differences, and inoculated sweetpotatoes had a significantly higher number of flies carrying C. fimbriata. This study suggests that D. hydei can carry C. fimbriata from infected sweetpotatoes and move viable C. fimbriata inocula both externally and internally, making this the first report of any Drosophila sp. serving as a potential vector for the Ceratocystis genus.
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Drosophila , Insetos Vetores , Ipomoea batatas , Doenças das Plantas , Animais , Ipomoea batatas/microbiologia , Doenças das Plantas/microbiologia , Drosophila/microbiologia , Insetos Vetores/microbiologia , North Carolina , Ascomicetos/fisiologia , Raízes de Plantas/microbiologiaRESUMO
The landscape of scientific publishing is experiencing a transformative shift toward open access, a paradigm that mandates the availability of research outputs such as data, code, materials, and publications. Open access provides increased reproducibility and allows for reuse of these resources. This article provides guidance for best publishing practices of scientific research, data, and associated resources, including code, in The American Phytopathological Society journals. Key areas such as diagnostic assays, experimental design, data sharing, and code deposition are explored in detail. This guidance aligns with that observed by other leading journals. We hope the information assembled in this paper will raise awareness of best practices and enable greater appraisal of the true effects of biological phenomena in plant pathology.
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Patologia Vegetal , Reprodutibilidade dos Testes , Editoração/normas , Guias como Assunto , Acesso à Informação , Disseminação de InformaçãoRESUMO
In 2015, sweetpotato producers in the United States experienced one of the worst outbreaks of black rot recorded in history, with up to 60% losses reported in the field and packing houses and at shipping ports. Host resistance remains the ideal management tool to decrease crop losses. Lack of knowledge of Ceratocystis fimbriata biology represents a critical barrier for the deployment of resistance to black rot in sweetpotato. In this study, we scanned the recent near chromosomal-level assembly for putative secreted effectors in the sweetpotato C. fimbriata isolate AS236 using a custom fungal effector annotation pipeline. We identified a set of 188 putative effectors on the basis of secretion signal and in silico prediction in EffectorP. We conducted a deep RNA time-course sequencing experiment to determine whether C. fimbriata modulates effectors in planta and to define a candidate list of effectors expressed during infection. We examined the expression profile of two C. fimbriata isolates, a pre-epidemic (1990s) isolate and a post-epidemic (2015) isolate. Our in planta expression profiling revealed clusters of co-expressed secreted effector candidates. Based on fold-change differences of putative effectors in both isolates and over the course of infection, we suggested prioritization of 31 effectors for functional characterization. Among this set, we identified several effectors that provide evidence for a marked biotrophic phase in C. fimbriata during infection of sweetpotato storage roots. Our study revealed a catalog of effector proteins that provide insight into C. fimbriata infection mechanisms and represent a core catalog to implement effector-assisted breeding in sweetpotato. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.
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Ascomicetos , Ascomicetos/genética , Melhoramento Vegetal , Ceratocystis/genética , Sequência de BasesRESUMO
In 1922, Phytophthora capsici was described by Leon Hatching Leonian as a new pathogen infecting pepper (Capsicum annuum), with disease symptoms of root rot, stem and fruit blight, seed rot, and plant wilting and death. Extensive research has been conducted on P. capsici over the last 100 years. This review succinctly describes the salient mile markers of research on P. capsici with current perspectives on the pathogen's distribution, economic importance, epidemiology, genetics and genomics, fungicide resistance, host susceptibility, pathogenicity mechanisms, and management.
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Capsicum , Fungicidas Industriais , Phytophthora , Phytophthora/genética , Doenças das PlantasRESUMO
Management of cucurbit downy mildew (CDM) caused by Pseudoperonospora cubensis, relies on an intensive fungicide program. In Michigan, CDM occurs annually due to an influx of airborne sporangia and timely alerts of airborne inoculum can assist growers in assessing the need to initiate fungicide sprays. This research aimed to improve the specific detection of airborne P. cubensis sporangia by adapting quantitative real-time polymerase chain reaction (qPCR) assays to distinguish among P. cubensis clades I and II and P. humuli in spore trap samples from commercial production sites and research plots. We also evaluated the suitability of impaction spore traps compared with Burkard traps for detection of airborne sporangia. A multiplex qPCR assay improved the specificity of P. cubensis clade II detection accelerating the assessment of field spore trap samples. After 2 years of monitoring, P. cubensis clade II DNA was detected in spore trap samples before CDM symptoms were first observed in cucumber fields (July and August), while P. cubensis clade I DNA was not detected in air samples before or after the disease onset. In some commercial cucumber fields, P. humuli DNA was detected throughout the growing season. The Burkard spore trap appeared to be better suited for recovery of sporangia at low concentrations than the impaction spore trap. This improved methodology for the monitoring of airborne Pseudoperonospora spp. sporangia could be used as part of a CDM risk advisory system to time fungicide applications that protect cucurbit crops in Michigan.
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Cucumis sativus , Fungicidas Industriais , Oomicetos , Peronospora , DNA Mitocondrial , Gerenciamento Clínico , Fungicidas Industriais/farmacologia , Marcadores Genéticos , Oomicetos/genética , Peronospora/genética , Doenças das Plantas/prevenção & controle , EsporângiosRESUMO
Phytophthora capsici epidemics are propelled by warm temperatures and wet conditions. With temperatures and inland flooding in many locations worldwide expected to rise as a result of global climate change, understanding of population structure can help to inform management of P. capsici in the field and prevent devastating epidemics. Thus, we investigated the effect of host crop, geographical origin, fungicide sensitivity, and mating type on shaping the population structure of P. capsici in the eastern United States. Our fungicide in vitro assays identified the emergence of insensitive isolates for fluopicolide and mefenoxam. A set of 12 microsatellite markers proved informative to assign 157 P. capsici isolates to five distinct genetic clusters. Implementation of Bayesian structure, population differentiation, genetic diversity statistics, and index of association analysis, allowed us to identify population structure by host with some correspondence with genetic clusters for cucumber and squash isolates. We found weak population structure by state for geographically close isolates. In this study, we discovered that North Carolina populations stratify by fluopicolide sensitivity with insensitive isolates experiencing nonrandom mating. Our findings highlight the need for careful monitoring of local field populations, improved selection of relevant isolates for breeding efforts, and hypervigilant surveillance of resistance to different fungicides.
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Fungicidas Industriais , Phytophthora , Teorema de Bayes , Benzamidas , Fungicidas Industriais/farmacologia , Geografia , Phytophthora/genética , Melhoramento Vegetal , Doenças das PlantasRESUMO
Pseudoperonospora humuli is an obligate biotrophic oomycete that causes downy mildew, one of the most devastating diseases of cultivated hop, Humulus lupulus. Downy mildew occurs in all production areas of the crop in the Northern Hemisphere and Argentina. The pathogen overwinters in hop crowns and roots, and causes considerable crop loss. Downy mildew is managed by sanitation practices, planting of resistant cultivars, and fungicide applications. However, the scarcity of sources of host resistance and fungicide resistance in pathogen populations complicates disease management. This review summarizes the current knowledge on the symptoms of the disease, life cycle, virulence factors, and management of hop downy mildew, including various forecasting systems available in the world. Additionally, recent developments in genomics and effector discovery, and the future prospects of using such resources in successful disease management are also discussed. TAXONOMY: Class: Oomycota; Order: Peronosporales; Family: Peronosporaceae; Genus: Pseudoperonospora; Species: Pseudoperonospora humuli. DISEASE SYMPTOMS: The disease is characterized by systemically infected chlorotic shoots called "spikes". Leaf symptoms and signs include angular chlorotic lesions and profuse sporulation on the abaxial side of the leaf. Under severe disease pressure, dark brown discolouration or lesions are observed on cones. Infected crowns have brown to black streaks when cut open. Cultivars highly susceptible to crown rot may die at this phase of the disease cycle without producing shoots. However, foliar symptoms may not be present on plants with systemically infected root systems. INFECTION PROCESS: Pathogen mycelium overwinters in buds and crowns, and emerges on infected shoots in spring. Profuse sporulation occurs on infected tissues and sporangia are released and dispersed by air currents. Under favourable conditions, sporangia germinate and produce biflagellate zoospores that infect healthy tissue, thus perpetuating the infection cycle. Though oospores are produced in infected tissues, their role in the infection cycle is not defined. CONTROL: Downy mildew on hop is managed by a combination of sanitation practices and timely fungicide applications. Forecasting systems are used to time fungicide applications for successful management of the disease. USEFUL WEBSITES: https://content.ces.ncsu.edu/hop-downy-mildew (North Carolina State University disease factsheet), https://www.canr.msu.edu/resources/michigan-hop-management-guide (Michigan Hop Management Guide), http://uspest.org/risk/models (Oregon State University Integrated Plant Protection Center degree-day model for hop downy mildew), https://www.usahops.org/cabinet/data/Field-Guide.pdf (Field Guide for Integrated Pest Management in Hops).
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Humulus/parasitologia , Oomicetos/fisiologia , Doenças das Plantas/parasitologia , Resistência à Doença , Fungicidas Industriais , Humulus/imunologia , Doenças das Plantas/imunologia , Doenças das Plantas/prevenção & controleRESUMO
Hop powdery mildew, caused by the ascomycete fungus Podosphaera macularis, is a consistent threat to sustainable hop production. The pathogen utilizes two reproductive strategies for overwintering and perennation: (i) asexual vegetative hyphae on dormant buds that emerge the following season as infected shoots; and (ii) sexual ascocarps (chasmothecia), which are discharged during spring rain events. We demonstrate that P. macularis chasmothecia, in the absence of any asexual P. macularis growth forms, are a viable overwintering source capable of causing early season infection two to three orders of magnitude greater than that reported for perennation via asexual growth. Two epidemiological models were defined that describe (i) temperature-driven maturation of P. macularis chasmothecia; and (ii) ascosporic discharge in response to duration of leaf wetness and prevailing temperatures. P. macularis ascospores were confirmed to be infectious at temperatures ranging from 5 to 20°C. The organism's chasmothecia were also found to adhere tightly to the host tissue on which they formed, suggesting that these structures likely overwinter wherever hop tissue senesces within a hop yard. These observations suggest that existing early season disease management practices are especially crucial to controlling hop powdery mildew in the presence of P. macularis chasmothecia. Furthermore, these insights provide a baseline for the validation of weather-driven models describing maturation and release of P. macularis ascospores, models that can eventually be incorporated into hop disease management programs.
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Ascomicetos , Humulus , Doenças das Plantas/microbiologia , Ascomicetos/patogenicidade , Humulus/microbiologiaRESUMO
Downy mildews affect important crops and cause severe losses in production worldwide. Accurate identification and monitoring of these plant pathogens, especially at early stages of the disease, is fundamental in achieving effective disease control. The rapid development of molecular methods for diagnosis has provided more specific, fast, reliable, sensitive, and portable alternatives for plant pathogen detection and quantification than traditional approaches. In this review, we provide information on the use of molecular markers, serological techniques, and nucleic acid amplification technologies for downy mildew diagnosis, highlighting the benefits and disadvantages of the technologies and target selection. We emphasize the importance of incorporating information on pathogen variability in virulence and fungicide resistance for disease management and how the development and application of diagnostic assays based on standard and promising technologies, including high-throughput sequencing and genomics, are revolutionizing the development of species-specific assays suitable for in-field diagnosis. Our review provides an overview of molecular detection technologies and a practical guide for selecting the best approaches for diagnosis.
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The ability to detect and quantify aerially dispersed plant pathogens is essential for developing effective disease control measures and epidemiological models that optimize the timing for control. There is an acute need for managing the downy mildew pathogens infecting cucurbits and hop incited by members of the genus Pseudoperonospora (Pseudoperonospora cubensis clade 1 and 2 isolates and Pseudoperonospora humuli, respectively). A highly specific multiplex TaqMan quantitative polymerase chain reaction (PCR) assay targeting unique sequences in the pathogens' mitochondrial genomes was developed that enables detection of all three taxa in a single multiplexed amplification. An internal control included in the reaction evaluated whether results were influenced by PCR inhibitors that can make it through the DNA extraction process. Reliable quantification of inoculum as low as three sporangia in a sample was observed. The multiplexed assay was tested with DNA extracted from purified sporangia, infected plant tissue, and environmental samples collected on impaction spore traps samplers. The ability to accurately detect and simultaneously quantify all three pathogens in a single multiplexed amplification should improve management options for controlling the diseases they cause.
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Oomicetos , Peronospora , Modelos Epidemiológicos , Oomicetos/genética , Doenças das Plantas , EsporângiosRESUMO
Black rot, caused by Ceratocystis fimbriata, is a devastating postharvest disease of sweetpotato that recently re-emerged in 2014. Although the disease is known to develop in storage and during export to overseas markets, little is known as to how pathogen dispersal occurs. This study was designed to investigate dump tank water as a means of dispersal through four different types of water treatments: inoculum concentration (0, 5, 5 × 101, 5 × 102, and 5 × 103 spores/ml), inoculum age (0, 24, 48, 96, and 144 h), water temperature (10°C, 23°C, 35°C, and 45°C), and presence of a water sanitizer (DryTec, SaniDate, FruitGard, and Selectrocide). Wounded and nonwounded sweetpotato storage roots were soaked in each water treatment for 20 min, stored at 29°C for a 14-day period, and rated for disease incidence every other day. Disease was observed in sweetpotato storage roots in all water treatments tested, except in the negative controls. Disease incidence decreased with both inoculum concentration and inoculum age, yet values of 16.26% and up to 50% were observed for roots exposed to 5 spores/ml and 144-h water treatments, respectively. Sanitizer products that contained a form of chlorine as the active ingredient significantly reduced disease incidence in storage roots when compared with control roots and roots exposed to a hydrogen-peroxide based product. Finally, no significant differences in final incidence were detected in wounded sweetpotato storage roots exposed to water treatments of any temperature, but a significant reduction in disease progression was observed in the 45°C treatment. These findings indicate that if packing line dump tanks are improperly managed, they can aid C. fimbriata dispersal through the build-up of inoculum as infected roots are unknowingly washed after storage. Chlorine-based sanitizers can reduce infection when applied after root washing and not in the presence of high organic matter typically found in dump tanks.
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Ipomoea batatas , Ceratocystis , Temperatura , ÁguaRESUMO
Pseudoperonospora humuli is an obligate biotrophic oomycete that causes downy mildew (DM), one of the most destructive diseases of cultivated hop that can lead to 100% crop loss in susceptible cultivars. We used the published genome of P. humuli to predict the secretome and effectorome and analyze the transcriptome variation among diverse isolates and during infection of hop leaves. Mining the predicted coding genes of the sequenced isolate OR502AA of P. humuli revealed a secretome of 1,250 genes. We identified 296 RXLR and RXLR-like effector-encoding genes in the secretome. Among the predicted RXLRs, there were several WY-motif-containing effectors that lacked canonical RXLR domains. Transcriptome analysis of sporangia from 12 different isolates collected from various hop cultivars revealed 754 secreted proteins and 201 RXLR effectors that showed transcript evidence across all isolates with reads per kilobase million (RPKM) values > 0. RNA-seq analysis of OR502AA-infected hop leaf samples at different time points after infection revealed highly expressed effectors that may play a relevant role in pathogenicity. Quantitative RT-PCR analysis confirmed the differential expression of selected effectors. We identified a set of P. humuli core effectors that showed transcript evidence in all tested isolates and elevated expression during infection. These effectors are ideal candidates for functional analysis and effector-assisted breeding to develop DM resistant hop cultivars.
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Pythium ultimum causes seedling damping-off and root and crown rot in greenhouse ornamental plants. To understand the population dynamics and assess population structure of P. ultimum in Michigan floriculture crops, simple sequence repeats (SSRs) were developed using the previously published P. ultimum predicted transcriptome. A total of 166 isolates sampled from 2011 to 2013 from five, one, and three greenhouses in Kalamazoo, Kent, and Wayne Counties, respectively, were analyzed using six polymorphic and fluorescently labeled SSR markers. The average unbiased Simpson's index (λu, 0.95), evenness (E5, 0.56), and recovery of 12 major clones out of the 65 multilocus genotypes obtained, suggests that P. ultimum is not a recent introduction into Michigan greenhouses. Analyses revealed a clonal population, with limited differentiation among seasons, hosts, and counties sampled. Results also indicated the presence of common genotypes among years, suggesting that sanitation measures should be enhanced to eradicate resident P. ultimum populations. Finally, the presence of common genotypes among counties suggests that there is an exchange of infected plant material among greenhouse facilities, or that there is a common source of inoculum coming to the region. Continued monitoring of pathogen populations will enhance our understanding of population dynamics of P. ultimum in Michigan and facilitate improvement of control strategies.
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Doenças das Plantas , Pythium , Genótipo , Michigan , Doenças das Plantas/microbiologia , Plantas/microbiologia , Dinâmica Populacional , Pythium/classificação , Pythium/genética , PlântulaRESUMO
Downy mildews are plant pathogens that damage crop quality and yield worldwide. Among the most severe and notorious crop epidemics of downy mildew occurred on grapes in the mid-1880s, which almost destroyed the wine industry in France. Since then, there have been multiple outbreaks on sorghum and millet in Africa, tobacco in Europe, and recent widespread epidemics on lettuce, basil, cucurbits, and spinach throughout North America. In the mid-1970s, loss of corn to downy mildew in the Philippines was estimated at US$23 million. Today, crops that are susceptible to downy mildews are worth at least $7.5 billion of the United States' economy. Although downy mildews cause devastating economic losses in the United States and globally, this pathogen group remains understudied because they are difficult to culture and accurately identify. Early detection of downy mildews in the environment is critical to establish pathogen presence and identity, determine fungicide resistance, and understand how pathogen populations disperse. Knowing when and where pathogens emerge is also important for identifying critical control points to restrict movement and to contain populations. Reducing the spread of pathogens also decreases the likelihood of sexual recombination events and discourages the emergence of novel virulent strains. A major challenge in detecting downy mildews is that they are obligate pathogens and thus cannot be cultured in artificial media to identify and maintain specimens. However, advances in molecular detection techniques hold promise for rapid and in some cases, relatively inexpensive diagnosis. In this article, we discuss recent advances in diagnostic tools that can be used to detect downy mildews. First, we briefly describe downy mildew taxonomy and genetic loci used for detection. Next, we review issues encountered when identifying loci and compare various traditional and novel platforms for diagnostics. We discuss diagnosis of downy mildew traits and issues to consider when detecting this group of organisms in different environments. We conclude with challenges and future directions for successful downy mildew detection.
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Peronospora , Doenças das Plantas , Oomicetos/classificação , Oomicetos/genética , Peronospora/classificação , Peronospora/genética , Doenças das Plantas/etiologia , Doenças das Plantas/microbiologiaRESUMO
Pseudoperonospora cubensis, the causal agent of cucurbit downy mildew (CDM), is known to exhibit host specialization. The virulence of different isolates of the pathogen can be classified into pathotypes based on their compatibility with a differential set composed of specific cucurbit host types. However, the genetic basis of host specialization within P. cubensis is not yet known. Total genomic DNA extracted from nine isolates of P. cubensis collected from 2008 to 2013 from diverse cucurbit host types (Cucumis sativus, C. melo var. reticulatus, Cucurbita maxima, C. moschata, C. pepo, and Citrullus lanatus) in the United States were subjected to whole-genome sequencing. Comparative analysis of these nine genomes confirmed the presence of two distinct evolutionary lineages (lineages I and II) of P. cubensis. Many fixed polymorphisms separated lineage I comprising isolates from Cucurbita pepo, C. moschata, and Citrullus lanatus from lineage II comprising isolates from Cucumis spp. and Cucurbita maxima. Phenotypic characterization showed that lineage II isolates were of the A1 mating type and belonged to pathotypes 1 and 3 that were not known to be present in the United States prior to the resurgence of CDM in 2004. The association of lineage II isolates with the new pathotypes and a lack of genetic diversity among these isolates suggest that lineage II of P. cubensis is associated with the resurgence of CDM on cucumber in the United States.
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Downy mildew pathogens affect several economically important crops worldwide but, due to their obligate nature, few genetic resources are available for genomic and population analyses. Draft genomes for emergent downy mildew pathogens such as the oomycete Pseudoperonospora cubensis, causal agent of cucurbit downy mildew, have been published and can be used to perform comparative genomic analysis and develop tools such as microsatellites to characterize pathogen population structure. We used bioinformatics to identify 2,738 microsatellites in the P. cubensis predicted transcriptome and evaluate them for transferability to the hop downy mildew pathogen, Pseudoperonospora humuli, since no draft genome is available for this species. We also compared the microsatellite repertoire of P. cubensis to that of the model organism Hyaloperonospora arabidopsidis, which causes downy mildew in Arabidopsis. Although trends in frequency of motif-type were similar, the percentage of SSRs identified from P. cubensis transcripts differed significantly from H. arabidopsidis. The majority of a subset of microsatellites selected for laboratory validation (92%) produced a product in P. cubensis isolates, and 83 microsatellites demonstrated transferability to P. humuli. Eleven microsatellites were found to be polymorphic and consistently amplified in P. cubensis isolates. Analysis of Pseudoperonospora isolates from diverse hosts and locations revealed higher diversity in P. cubensis compared to P. humuli isolates. These microsatellites will be useful in efforts to better understand relationships within Pseudoperonospora species and P. cubensis on a population level.
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The resurgence of cucurbit downy mildew has dramatically influenced production of cucurbits and disease management systems at multiple scales. Long-distance dispersal is a fundamental aspect of epidemic development that influences the timing and extent of outbreaks of cucurbit downy mildew. The dispersal potential of Pseudoperonospora cubensis appears to be limited primarily by sporangia production in source fields and availability of susceptible hosts and less by sporangia survival during transport. Uncertainty remains regarding the role of locally produced inoculum in disease outbreaks, but evidence suggests multiple sources of primary inoculum could be important. Understanding pathogen diversity and population differentiation is a critical aspect of disease management and an active research area. Underpinning advances in our understanding of pathogen biology and disease management has been the research capacity and coordination of stakeholders, scientists, and extension personnel. Concepts and approaches developed in this pathosystem can guide future efforts when responding to incursions of new or reemerging downy mildew pathogens.
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Cucurbitaceae/microbiologia , Oomicetos/fisiologia , Doenças das Plantas/microbiologia , Produção AgrícolaRESUMO
The downy mildew pathogen, Pseudoperonospora cubensis, which infects plant species in the family Cucurbitaceae, has undergone major changes during the last decade. Disease severity and epidemics are far more destructive than previously reported, and new genotypes, races, pathotypes, and mating types of the pathogen have been discovered in populations from around the globe as a result of the resurgence of the disease. Consequently, disease control through host plant resistance and fungicide applications has become more complex. This resurgence of P. cubensis offers challenges to scientists in many research areas including pathogen biology, epidemiology and dispersal, population structure and population genetics, host preference, host-pathogen interactions and gene expression, genetic host plant resistance, inheritance of host and fungicide resistance, and chemical disease control. This review serves to summarize the current status of this major pathogen and to guide future management and research efforts within this pathosystem.
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Cucurbitaceae/microbiologia , Oomicetos/fisiologia , Cucurbitaceae/genética , Resistência Microbiana a Medicamentos , Europa (Continente) , Fungicidas Industriais , Interações Hospedeiro-Patógeno/genética , Controle de Pragas , Doenças das Plantas , Imunidade Vegetal/genética , Estados UnidosRESUMO
Leaf curling and petiole twisting of celery (Apium graveolens) were observed in several commercial fields in five Michigan counties in 2010 through 2012, causing significant crop damage and loss. Prior to this time, the pathogen Colletotrichum acutatum species complex had not been previously associated with celery in Michigan. In this study, the pathogen's genotype and phenotype were characterized, the influence of environmental conditions determined, and fungicides tested. Pathogen identification was based on conidial morphology and molecular identification using species-specific primers. Intersimple-sequence repeat (ISSR) banding patterns were similar between C. acutatum isolates from celery (n = 51) and blueberry (n = 1) but different from C. dematium and C. gloeosporioides. Four ISSR primers resulted in 4% polymorphism when tested on isolates from celery. Pathogenicity and virulence of C. acutatum sensu lato isolated from celery (n = 81), tomato (n = 2), and blueberry (n = 1) were evaluated in greenhouse experiments, which revealed differences in virulence among isolates but no significant differences specific to collection year, county, or field. In dew chambers and growth chambers, high temperatures (≥25°C) or long leaf wetness duration (>24 h) increased disease incidence. Twelve fungicides were tested in field studies over two growing seasons to determine their efficacy against celery anthracnose. The fungicides azoxystrobin, pyraclostrobin, mancozeb, and chlorothalonil reduced disease by 27 to 50% compared with the untreated control when disease pressure was moderate.
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Eggplant (Solanum melongena L.) is an important solanaceous crop with high phenotypic diversity and moderate genotypic diversity. Ninety-nine genotypes of eggplant germplasm (species (S. melongena, S. incanum, S. linnaeanum and S. gilo), landraces and heirloom cultivars) from 32 countries and five continents were evaluated for genetic diversity, population structure, fruit shape, and disease resistance to Phytophthora fruit rot. Fruits from each line were measured for fruit shape and evaluated for resistance to two Phytophthora capsici isolates seven days post inoculation. Only one accession (PI 413784) was completely resistant to both isolates evaluated. Partial resistance to Phytophthora fruit rot was found in accessions from all four eggplant species evaluated in this study. Genetic diversity and population structure were assessed using 22 polymorphic simple sequence repeats (SSRs). The polymorphism information content (PIC) for the population was moderate (0.49) in the population. Genetic analyses using the program STRUCTURE indicated the existence of four genetic clusters within the eggplant collection. Population structure was detected when eggplant lines were grouped by species, continent of origin, country of origin, fruit shape and disease resistance.