Showing papers in "Annual Review of Phytopathology in 2003"
TL;DR: A model describing the sequence of events leading from initial infection to the induction of defense genes is presented and exciting new data suggest that the mobile signal for SAR might be a lipid molecule.
Abstract: Systemic acquired resistance (SAR) is a mechanism of induced defense that confers long-lasting protection against a broad spectrum of microorganisms. SAR requires the signal molecule salicylic acid (SA) and is associated with accumulation of pathogenesis-related proteins, which are thought to contribute to resistance. Much progress has been made recently in elucidating the mechanism of SAR. Using the model plant Arabidopsis, it was discovered that the isochorismate pathway is the major source of SA during SAR. In response to SA, the positive regulator protein NPR1 moves to the nucleus where it interacts with TGA transcription factors to induce defense gene expression, thus activating SAR. Exciting new data suggest that the mobile signal for SAR might be a lipid molecule. We discuss the molecular and genetic data that have contributed to our understanding of SAR and present a model describing the sequence of events leading from initial infection to the induction of defense genes.
2,744 citations
TL;DR: This review examines the discovery of naturally occurring phytochemicals antagonistic toward plant-parasitic and other nematodes.
Abstract: ■ Abstract This review examines the discovery of naturally occurring phytochemicals antagonistic toward plant-parasitic and other nematodes. Higher plants have yielded a broad spectrum of active compounds, including polythienyls, isothiocyanates, glucosinolates, cyanogenic glycosides, polyacetylenes, alkaloids, lipids, terpenoids, sesquiterpenoids, diterpenoids, quassinoids, steroids, triterpenoids, simple and complex phenolics, and several other classes. Many other antinematodal compounds have been isolated from biocontrol and other fungi. Natural products active against mammalian parasites can serve as useful sources of compounds for examination of activity against plant parasites. The agricultural utilization of phytochemicals, although currently uneconomic in many situations, offers tremendous potential.
824 citations
TL;DR: One challenge in future biocontrol research involves development of new strategies to overcome the broad toxicity and lack of antifungal specificity displayed by most biOControl antibiotics studied so far.
Abstract: Certain strains of fluorescent pseudomonads are important biological components of agricultural soils that are suppressive to diseases caused by pathogenic fungi on crop plants. The biocontrol abilities of such strains depend essentially on aggressive root colonization, induction of systemic resistance in the plant, and the production of diffusible or volatile antifungal antibiotics. Evidence that these compounds are produced in situ is based on their chemical extraction from the rhizosphere and on the expression of antibiotic biosynthetic genes in the producer strains colonizing plant roots. Well-characterized antibiotics with biocontrol properties include phenazines, 2,4-diacetylphloroglucinol, pyoluteorin, pyrrolnitrin, lipopeptides, and hydrogen cyanide. In vitro, optimal production of these compounds occurs at high cell densities and during conditions of restricted growth, involving (i) a number of transcriptional regulators, which are mostly pathway-specific, and (ii) the GacS/GacA two-component system, which globally exerts a positive effect on the production of extracellular metabolites at a posttranscriptional level. Small untranslated RNAs have important roles in the GacS/GacA signal transduction pathway. One challenge in future biocontrol research involves development of new strategies to overcome the broad toxicity and lack of antifungal specificity displayed by most biocontrol antibiotics studied so far.
788 citations
TL;DR: Several QTL have been identified for lower FHB severity, DON content, and kernel discoloration and used to enhance F HB resistance in barley and marker-assisted selection for FHB resistance QTL on 3BS of wheat and on 2H of barley is in progress.
Abstract: Fusarium head blight (FHB) is a devastating disease of wheat and barley worldwide. Resistant cultivars could reduce damage from FHB. Chinese wheat cultivar Sumai 3 and its derivatives represent the greatest degree of resistance to FHB known. A major quantitative trait locus (QTL) on chromosome 3BS and other minor QTL for FHB resistance have been identified in these cultivars and used in wheat-breeding programs worldwide. Many breeding lines with the 3BS resistance QTL and improved agronomic traits have been developed. In barley, only limited sources of FHB resistance are available, especially in six-rowed barley, and none of them contains a DON level low enough to meet the safety requirement of the brewing industry. Several QTL have been identified for lower FHB severity, DON content, and kernel discoloration and used to enhance FHB resistance in barley. Marker-assisted selection for FHB resistance QTL on 3BS of wheat and on 2H of barley is in progress.
745 citations
TL;DR: The role of antibiotic use on plants in the antibiotic-resistance crisis in human medicine is the subject of debate.
Abstract: Antibiotics have been used since the 1950s to control certain bacterial diseases of high-value fruit, vegetable, and ornamental plants. Today, the antibiotics most commonly used on plants are oxytetracycline and streptomycin. In the USA, antibiotics applied to plants account for less than 0.5% of total antibiotic use. Resistance of plant pathogens to oxytetracycline is rare, but the emergence of streptomycin-resistant strains of Erwinia amylovora, Pseudomonas spp., and Xanthomonas campestris has impeded the control of several important diseases. A fraction of streptomycin-resistance genes in plant-associated bacteria are similar to those found in bacteria isolated from humans, animals, and soil, and are associated with transfer-proficient elements. However, the most common vehicles of streptomycin-resistance genes in human and plant pathogens are genetically distinct. Nonetheless, the role of antibiotic use on plants in the antibiotic-resistance crisis in human medicine is the subject of debate.
707 citations
TL;DR: The development of Pseudomonas for the control of Pythium diseases in hydroponics and Pseudozyma flocculosa for theControl of powdery mildew by two Canadian research programs is presented.
Abstract: The controlled environment of greenhouses, the high value of the crops, and the limited number of registered fungicides offer a unique niche for the biological control of plant diseases. During the past ten years, over 80 biocontrol products have been marketed worldwide. A large percentage of these have been developed for greenhouse crops. Products to control soilborne pathogens such as Sclerotinia, Pythium, Rhizoctonia and Fusarium include Coniothyrium minitans, species of Gliocladium, Trichoderma, Streptomyces, and Bacillus, and nonpathogenic Fusarium. Products containing Trichoderma, Ampelomyces quisqualis, Bacillus, and Ulocladium are being developed to control the primary foliar diseases, Botrytis and powdery mildew. The development of Pseudomonas for the control of Pythium diseases in hydroponics and Pseudozyma flocculosa for the control of powdery mildew by two Canadian research programs is presented. In the future, biological control of diseases in greenhouses could predominate over chemical pesticides, in the same way that biological control of greenhouse insects predominates in the United Kingdom. The limitations in formulation, registration, and commercialization are discussed, along with suggested future research priorities.
582 citations
TL;DR: This review describes how phytopathogenic bacteria have incorporated QS mechanisms into complex regulatory cascades that control genes for pathogenicity and colonization of host surfaces.
Abstract: ■ Abstract Quorum sensing (QS) allows bacteria to assess their local population density and/or physical confinement via the secretion and detection of small, diffusible signal molecules. This review describes how phytopathogenic bacteria have incorporated QS mechanisms into complex regulatory cascades that control genes for pathogenicity and colonization of host surfaces. Traits regulated by QS include the production of extracellular polysaccharides, degradative enzymes, antibiotics, siderophores, and pigments, as well as Hrp protein secretion, Ti plasmid transfer, motility, biofilm formation, and epiphytic fitness. Since QS regulatory systems are often required for pathogenesis, interference with QS signaling may offer a means of controlling bacterial diseases of plants. Several bacterial pathogens of plants that have been intensively studied and have revealed information of both fundamental and practical importance are reviewed here: Agrobacterium tumefaciens , Pantoea stewartii, Erwinia carotovora, Ralstonia solanacearum, Pseudomonas syringae, Pseudomonas aeruginosa, and Xanthomonas campestris .
554 citations
TL;DR: Efforts to control infection or mycotoxin development through conventional breeding and genetic engineering are reviewed and the role of transgenic insect control in the prevention of mycotoxins in maize is discussed.
Abstract: ▪ Abstract Infection of maize kernels by toxigenic fungi remains a challenging problem despite decades of research progress. Cultural practices, including crop rotation, tillage, planting date, and management of irrigation and fertilization, have limited effects on infection and subsequent mycotoxin accumulation. Current infrastructure and grain storage practices in developed countries can prevent postharvest development of mycotoxins, but this aspect remains a threat in developing countries, especially in tropical areas. Because most mycotoxin problems develop in the field, strategies are needed to prevent infection of growing plants by toxigenic fungi. Developing genetic resistance to Aspergillus flavus, Gibberella zeae, and Fusarium spp. (particularly F. verticillioides) in maize is a high priority. Sources of resistance to each of these pathogens have been identified and have been incorporated into public and private breeding programs. However, few, if any, commercial cultivars have adequate levels of...
425 citations
TL;DR: Members of the Luteoviridae are transmitted by aphids in a circulative, nonpropagative manner that requires the virus to be acquired through gut tissue into the aphid hemocoel and then exit through salivary tissues.
Abstract: Members of the Luteoviridae are transmitted by aphids in a circulative, nonpropagative manner that requires the virus to be acquired through gut tissue into the aphid hemocoel and then exit through salivary tissues. This process is aphid species-specific and involves specific recognition of the virus by unidentified components on the membranes of gut and salivary tissues. Transport through the tissues is an endocytosis/exocytosis process. Both structural proteins of the virus are involved in the transmission process, with multiple protein domains regulating the movement and survival of the virus in the aphid and plant. Here we review what is known about the genetic, cellular, and molecular mechanisms regulating these complex and specific virus-aphid interactions.
365 citations
TL;DR: This review constructs a portrait of how biofilms associated with leaves, roots and within intercellular spaces influence the ecology of the bacteria they harbor and the relationship of bacteria with plants.
Abstract: Bacteria associated with plants have been observed frequently to form assemblages referred to as aggregates, microcolonies, symplasmata, or biofilms on leaves and on root surfaces and within intercellular spaces of plant tissues. In a wide range of habitats, biofilms are purported to be microniches of conditions markedly different from those of the ambient environment and drive microbial cells to effect functions not possible alone or outside of biofilms. This review constructs a portrait of how biofilms associated with leaves, roots and within intercellular spaces influence the ecology of the bacteria they harbor and the relationship of bacteria with plants. We also consider how biofilms may enhance airborne dissemination, ubiquity and diversification of plant-associated bacteria and may influence strategies for biological control of plant disease and for assuring food safety. Trapped by a nexus, coordinates uncertain Ever expanding or contracting Cannibalistic and scavenging sorties Excavations through signs of past alliances Consensus signals sound revelry Then time warped by viscosity Genomes showing codependence A virtual microbial beach party With no curfew and no time-out A few estranged cells seeking exit options, Looking for another menagerie. David Sands, Montana State University, Bozeman, February 2003
330 citations
TL;DR: The black box of how nematodes bring about such elaborate cell differentiation in the plant is starting to open and the groundwork is set so that the functions of the plant and nematode genes in feeding site development can begin to be assessed.
Abstract: The feeding sites induced by sedentary root-endoparasitic nematodes have long fascinated researchers. Nematode feeding sites are constructed from plant cells, modified by the nematode to feed itself. Powerful new techniques are allowing us to begin to elucidate the molecular mechanisms that produce the ultrastructural features in nematode feeding cells. Many plant genes that are expressed in feeding sites produced by different nematodes have been identified in several plant species. Nematode-responsive plant genes can now be grouped in categories related to plant developmental pathways and their roles in the making of a feeding site can be illuminated. The black box of how nematodes bring about such elaborate cell differentiation in the plant is also starting to open. Although the information is far from complete, the groundwork is set so that the functions of the plant and nematode genes in feeding site development can begin to be assessed.
TL;DR: The current standard treatment for management of soilborne pests in some high-value crop production systems is preplant fumigation with mixtures of methyl bromide and chloropicrin, but longer-term research goals have focused on developing a more integrated approach for pest management that incorporates the use of cultural practices to reduce pathogen pressure, host resistance to disease, and biological approaches for stimulating plant growth and control of root diseases.
Abstract: The current standard treatment for management of soilborne pests in some high-value crop production systems is preplant fumigation with mixtures of methyl bromide and chloropicrin. With the impending phase-out of methyl bromide, the agricultural industries that rely on soil fumigation face the need for development of alternative pest management strategies. To maintain farm productivity, immediate term research has focused on evaluation of alternative fumigants, modification of current crop production practices to accommodate their use, and improvement of application technologies to reduce the environmental effects of fumigant applications. Longer-term research goals have focused on developing a more integrated approach for pest management that incorporates the use of cultural practices to reduce pathogen pressure, host resistance to disease, and biological approaches for stimulating plant growth and control of root diseases.
TL;DR: Future work on this model system will focus on how the interaction of the Pto kinase with bacterial effector proteins activates signal transduction, defining the specific role of signaling components, and ultimately, determining which host defense responses are most responsible for inhibiting growth of the pathogen and suppressing symptoms of bacterial speck disease.
Abstract: The Pto gene in tomato confers gene-for-gene resistance to Pseudomonas syringae pv. tomato, the causative agent of bacterial speck disease. Pto was first introgressed from a wild species of tomato into cultivated tomato varieties over 60 years ago and is now widely used to control speck disease. Cloning of the Pto gene revealed that it encodes a cytoplasmically localized serine-threonine protein kinase. The molecular basis of gene-for-gene recognition in this pathosystem is the direct physical interaction of the Pto kinase with either of two Pseudomonas effector proteins, AvrPto and AvrPtoB. Upon recognition of AvrPto or AvrPtoB, the Pto kinase acts in concert with Prf, a leucine-rich repeat-containing protein, to activate multiple signal transduction pathways. There has been much progress in understanding the evolutionary origin of the Pto gene, structural details about how the Pto kinase interacts with AvrPto and AvrPtoB, signaling steps downstream of Pto, and defense responses activated by the Pto pathway. Future work on this model system will focus on how the interaction of the Pto kinase with bacterial effector proteins activates signal transduction, defining the specific role of signaling components, and ultimately, determining which host defense responses are most responsible for inhibiting growth of the pathogen and suppressing symptoms of bacterial speck disease.
TL;DR: In this article, the authors integrate functional responses with diversity to understand the role of mycorrhizae in ecosystems, and organize these into functional groups, and show how complex behavior can be generated using a simple matrix model of resource exchange.
Abstract: ▪ Abstract Mycorrhizae regulate elemental and energy flows in terrestrial ecosystems. We understand much of how mycorrhizae work, but integrating all possible mechanisms into a whole has proven elusive. Multiple evolutionary events and the long evolutionary history mean that different plants and fungi bring independent characteristics to the symbiosis. This variety results in extensive physiological variation. How do we integrate functional responses with diversity to understand the role of mycorrhizae in ecosystems? We review ecophysiological mechanisms of mycorrhizae and organize these into functional groups. Species-area relationships are not curvilinear, but resemble the “broken stick” model. We coupled functional groups with a metacommunity analysis to show how complex behavior can be generated using a simple matrix model of resource exchange. This approach provides insights into how we might integrate diversity and function across landscapes.
TL;DR: A review of recent developments in the use of optical methods for detecting foliar disease, evaluates the likely benefits of spatially selective disease control in field crops, and discusses practicalities and limitations of using optical disease detection systems for crop protection in precision pest management.
Abstract: There is increasing pressure to reduce the use of pesticides in modem crop production to decrease the environmental impact of current practice and to lower production costs. It is therefore imperative that sprays are only applied when and where needed. Since diseases in fields are frequently patchy, sprays may be applied unnecessarily to disease-free areas. Disease control could be more efficient if disease patches within fields could be identified and spray applied only to the infected areas. Recent developments in optical sensor technology have the potential to enable direct detection of foliar disease under field conditions. This review assesses recent developments in the use of optical methods for detecting foliar disease, evaluates the likely benefits of spatially selective disease control in field crops, and discusses practicalities and limitations of using optical disease detection systems for crop protection in precision pest management.
TL;DR: Understanding pathogen self-defense mechanisms for coping with antagonist assault provides a novel approach to improving the durability of biologically based disease control strategies and has implications for the deployment of transgenes.
Abstract: Natural and agricultural ecosystems harbor a wide variety of microorganisms that play an integral role in plant health, crop productivity, and preservation of multiple ecosystem functions. Interactions within and among microbial communities are numerous and range from synergistic and mutualistic to antagonistic and parasitic. Antagonistic and parasitic interactions have been exploited in the area of biological control of plant pathogenic microorganisms. To date, biocontrol is typically viewed from the perspective of how antagonists affect pathogens. This review examines the other face of this interaction: how plant pathogens respond to antagonists and how this can affect the efficacy of biocontrol. Just as microbial antagonists utilize a diverse arsenal of mechanisms to dominate interactions with pathogens, pathogens have surprisingly diverse responses to counteract antagonism. These responses include detoxification, repression of biosynthetic genes involved in biocontrol, active efflux of antibiotics, and antibiotic resistance. Understanding pathogen self-defense mechanisms for coping with antagonist assault provides a novel approach to improving the durability of biologically based disease control strategies and has implications for the deployment of transgenes (microorganisms or plants).
TL;DR: This review summarizes recent progress in the development of rapid real-time PCR protocols and evaluates their effectiveness in a proposed nationwide network of diagnostic laboratories that will facilitate rapid diagnostics and improved communication.
Abstract: Awareness of crop biosecurity and phytosanitation has been heightened since 9/11 and the unresolved anthrax releases in October 2001. Crops are highly vulnerable to accidental or deliberate introductions of crop pathogens from outside U.S. borders. Strategic thinking about protection against deliberate or accidental release of a plant pathogen is an urgent priority. Rapid detection will be the key to success. This review summarizes recent progress in the development of rapid real-time PCR protocols and evaluates their effectiveness in a proposed nationwide network of diagnostic laboratories that will facilitate rapid diagnostics and improved communication.
TL;DR: Studies of cAMP signaling in a variety of plant fungal pathogens are reviewed, pointing out similarities in infection mechanisms, conservation of signaling components, as well as instances of cross-talk with other signaling pathways.
Abstract: cAMP regulates morphogenesis and virulence in a wide variety of fungi including the plant pathogens. In saprophytic yeasts such as Saccharomyces cerevisiae, cAMP signaling plays an important role in nutrient sensing. In filamentous saprophytes, the cAMP pathway appears to play an integral role in vegetative growth and sporulation, with possible connections to mating. Infection-related morphogenesis includes sporulation (conidia and teliospores), formation of appressoria, infection hyphae, and sclerotia. Here, we review studies of cAMP signaling in a variety of plant fungal pathogens. The primary fungi to be considered include Ustilago maydis, Magnaporthe grisea, Cryphonectria parasitica, Colletotrichum and Fusarium species, and Erisyphe graminis. We also include related information on Trichoderma species that act as mycoparasites and biocontrol agents of phytopathogenic fungi. We point out similarities in infection mechanisms, conservation of signaling components, as well as instances of cross-talk with other signaling pathways.
TL;DR: This review focuses on rapid immunodiagnostic and DNA-based detection methods for known bacterial pathogens in plants or plant products, which often manifest no symptoms of disease.
Abstract: Disease diagnosis is based on a number of factors, including laboratory tests for pathogen identification. Rapid development of genomic techniques for characterization of bacteria over the past decade has greatly simplified and improved pathogen detection and identification, but DNA-based methods have not yet entirely replaced traditional culture and phenotypic tests in the plant industry. The first section of this review focuses on rapid immunodiagnostic and DNA-based detection methods for known bacterial pathogens in plants or plant products, which often manifest no symptoms of disease. The second section covers the broader topic of disease diagnosis and new methods for identifying and characterizing bacteria.
TL;DR: Analysis of mixed infections with two WSMV isolates suggests that about four viral genomes participate in systemic invasion of each tiller, which increases the role of stochastic processes on dynamics of plant virus population genetics and evolution.
Abstract: Like many other plant RNA viruses, Wheat streak mosaic virus (WSMV) sequence diversity within and among infected plants is low given the large number of virions produced. This may be explained by considering aspects of plant virus life history. Intracellular replication of RNA viruses is predominately linear, not exponential, which means that the rate at which mutations accumulate also is linear. Bottlenecks during systemic movement further limit diversity. Analysis of mixed infections with two WSMV isolates suggests that about four viral genomes participate in systemic invasion of each tiller. Low effective population size increases the role of stochastic processes on dynamics of plant virus population genetics and evolution. Despite low pair-wise diversity among isolates, the number of polymorphic sites within the U.S. population is about the same as between divergent strains or a sister species. Characteristics of polymorphism in the WSMV coat protein gene suggest that most variation appears neutral.
TL;DR: The development of a spotted wilt risk index has aided greatly in relaying information on the importance of using an integrated approach for managing this disease.
Abstract: Tomato spotted wilt caused by thrips-vectored tomato spotted wilt virus (TSWV) is a very serious problem in peanut (Arachis hypogaea L.) production. TSWV and the thrips Frankliniella fusca and Frankliniella occidentalis, which vector the virus, present a difficult and complicated challenge from the perspectives of both epidemiology and disease management. Simply controlling the vector typically has not resulted in control of spotted wilt. No single measure can currently provide adequate control of spotted wilt where severe epidemics occur. However, interdisciplinary investigations have resulted in development of integrated management systems that make use of moderately resistant cultivars and chemical and cultural practices, each of which helps to suppress spotted wilt epidemics. Such systems have been successfully deployed in many areas for minimizing losses to this disease. The development of a spotted wilt risk index has aided greatly in relaying information on the importance of using an integrated approach for managing this disease.
TL;DR: The cloning of race-specific resistance genes to powdery mildew infection and of genes required for their function provides first insights into molecular mechanisms enabling the host to recognize mildew effector components and suggests candidate mechanisms of resistance signaling.
Abstract: Parasitic biotrophs such as mildews and rusts evolved specific mechanisms that keep host cells alive during infection. These fungi appear to absorb nutrients mainly by proton-symport-driven transporter proteins that reside in specialized feeding structures. Accumulating evidence suggests that biotrophic fungi both suppress induction of plant defense responses in physical proximity to infection sites and induce specific host genes for the establishment of biotrophy. The peculiarities of biotrophic pathogenesis likely reflect diverse types of plant disease-resistance responses. The cloning of race-specific resistance genes to powdery mildew infection and of genes required for their function provides first insights into molecular mechanisms enabling the host to recognize mildew effector components and suggests candidate mechanisms of resistance signaling. Resistance to powdery mildew fungi that result from mutations in host genes promises to shed light on mechanisms that are required for the establishment of disease susceptibility.
TL;DR: This review addresses recent findings on the identification and characterization of host factors in BMV RNA replication, and characterizing the functions of these host factors is revealing basic aspects of virus RNA replication and helping to define the normal functions ofThese factors in the host.
Abstract: The replication of positive-strand RNA viruses is a complex multi-step process involving interactions between the viral genome, virus-encoded replication factors, and host factors. The plant virus brome mosaic virus (BMV) has served as a model for positive-strand RNA virus replication, recombination, and virion assembly. This review addresses recent findings on the identification and characterization of host factors in BMV RNA replication. To date, all characterized host factors facilitate steps that lead to assembly of a functional BMV RNA replication complex. Some of these host factors are required for regulation of viral gene expression. Others are needed to co-regulate BMV RNA translation and recruitment of BMV RNAs from translation to viral RNA replication complexes on the endoplasmic reticulum. Other host factors provide essential lipid modifications in the endoplasmic reticulum membrane or function as molecular chaperones to activate the replication complex. Characterizing the functions of these host factors is revealing basic aspects of virus RNA replication and helping to define the normal functions of these factors in the host.
TL;DR: Combining gene disruption strategies with new genomics technologies for expression profiling should help plant pathologists to understand the pathological and evolutionary significance of biological and chemical diversity in Gibberella and to identify novel strategies for disease control.
Abstract: Gibberella species are destructive plant pathogens, although many are more familiar under their Fusarium anamorph names. The recent synthesis of phylogenetic, biological, and morphological species approaches has revitalized taxonomy of a genus that was first described almost 200 years ago. Twelve sexual species of Gibberella of agricultural importance were selected for this review to represent phylogenetic, biological, and chemical diversity of the genus. Even closely related Gibberella species can differ in reproductive mode, geographic and host distribution, plant pathogenesis, and production of toxins and other biologically active metabolites. Gibberella species have proven amenable to meiotic and molecular genetic analysis; A complete genome sequence of G. zeae should soon be available. Combining gene disruption strategies with new genomics technologies for expression profiling should help plant pathologists to understand the pathological and evolutionary significance of biological and chemical diversity in Gibberella and to identify novel strategies for disease control.
TL;DR: Host/parasite interactions between plant parasitic nematodes (PPN) and animal parasitic nem atodes, with an emphasis on mammalian hosts (MPN), are compared and similarities and differences are considered in the context of progress on molecular dissection of these interactions.
Abstract: Parasitic nematodes that infect humans, animals, and plants cause serious diseases that are deleterious to human health and agricultural productivity. Chemical and biological control methods have reduced the impact of these parasites. However, surviving environmental stages lead to persistent reinfection of host species. In addition, development of resistance to nematicides and anthelmintics by these parasites and reduced availability of some nematicides, for environmental protection, pose significant obstacles for current and future prospects of effective parasite control. Due to marked differences in host species, research on animal and plant parasitic nematodes often proceeds independently. Despite the differences between animals and plants, basic cellular properties are shared among these host organisms. Some common properties may be important for mechanisms [homologous or convergent (homoplastic)] by which nematodes successfully infect these diverse hosts or by which animal and plant hosts resist infections by these pathogens. Here we compare host/parasite interactions between plant parasitic nematodes (PPN) and animal parasitic nematodes, with an emphasis on mammalian hosts (MPN). Similarities and differences are considered in the context of progress on molecular dissection of these interactions. A comprehensive coverage is not possible in the space allotted. Instead, an illustrative approach is used to establish examples that, it is hoped, exemplify the value of the comparative approach.
TL;DR: This review summarizes information on effectors that act directly against the nematode as well as those aimed at disrupting the Nematode feeding site and patterns of promoter activity that could deliver expression of these effectors in a restricted and directed manner.
Abstract: Biotechnology offers sustainable solutions to the problem of plant parasitic nematode control. There are several possible approaches for developing transgenic plants with improved nematode resistance; these include anti-invasion and migration strategies, feeding-cell attenuation, and antinematode feeding and development strategies. The essential elements of an effective control strategy are (a) genes that encode an antinematode effector protein, peptide or interfering RNA and (b) promoters that direct a specific pattern of expression for that effector. This review summarizes information on effectors that act directly against the nematode as well as those aimed at disrupting the nematode feeding site. We discuss patterns of promoter activity that could deliver expression of these effectors in a restricted and directed manner. Societal opposition to the technology of GM-nematode control is also discussed.
TL;DR: The argument is made that the country can become much better prepared to counter bioterrorism by developing a list of likely anti-crop threat agents that is based on a formal risk analysis, and making structural changes to the plant protection system.
Abstract: ▪ Abstract The U.S. National Research Council (NRC) concluded in 2002 that U.S. agriculture is vulnerable to attack and that the country has inadequate plans for dealing with agricultural bioterrorism. This article addresses the vulnerability of U.S. crops to attack from biological weapons by reviewing the costs and impact of plant diseases on crops, pointing out the difficulty in preventing deliberate introduction of pathogens and discovering new disease outbreaks quickly, and discussing why a plant pathogen might be chosen as a biological weapon. To put the threat into context, a brief historical review of anti-crop biological weapons programs is given. The argument is made that the country can become much better prepared to counter bioterrorism by developing a list of likely anti-crop threat agents, or categories of agents, that is based on a formal risk analysis; making structural changes to the plant protection system, such as expanding diagnostic laboratories, networking the laboratories in a nation...
TL;DR: Both Beet necrotic yellow vein virus and Beet soilborne mosaic virus are widespread and frequently found in the same field, infecting the same beet plant, and the implications of this close proximity are uncertain.
Abstract: Beet necrotic yellow vein virus (BNYVV) and Beet soilborne mosaic virus (BSBMV) are members of the genus Benyvirus, and Burdock mottle virus (BdMV) is a tentative member. BNYVV and BSBMV are vectored by the plasmodiophorid Polymyxa betae, which has a worldwide distribution. Polymyxa betae is morphologically indistinguishable from P. graminis, but recent molecular studies support separation of the two species. The geographic distribution of BNYVV is also worldwide, but BSBMV has been identified only in the United States. In Europe and Japan, several genotypic strains of BNYVV have been identified, and those with a fifth RNA appear to be more aggressive. No thorough survey of genotypic variability of BNYVV or BSBMV has been conducted in the United States. However, both viruses are widespread and frequently found in the same field, infecting the same beet plant. The implications of this close proximity, with regard to disease incidence and severity, and for recombination, are uncertain. Recent technological advances that permit improved detection and quantification of these viruses and their vector offer tremendous research opportunities.
TL;DR: In this paper, the type species of the genus Spiroplasma (Spiroplasmataceae, Mollicutes), S. citri, is restricted to the phloem sieve tubes and transmitted by Phloem sap-feeding insects.
Abstract: ▪ Abstract Spiroplasma citri, the type species of the genus Spiroplasma (Spiroplasmataceae, Mollicutes), is restricted to the phloem sieve tubes and transmitted by phloem sap-feeding insects, as is characteristic of the phytopathogenic mollicutes. The spiroplasmas are the only mollicutes showing motility and helical morphology, apparently mediated by a contractile fibrillar cytoskeleton bound to the inner surface of the spiroplasmal membrane. MreB genes, which are involved in cell-shape determination, have been identified in S. citri. Identified genes of other functional groups are those involved in the transmission of S. citri by the leafhoppers and genes coding for lipoproteins, including spiralin, bound to the outer surface of the spiroplasma membrane. S. citri mutants that are unable to use fructose induce only mild and delayed symptoms. Fructose utilization by the sieve tube-restricted wild-type spiroplasmas is postulated to deprive the companion cells of fructose, thereby impairing sucrose loading i...
TL;DR: There were no obvious trends in decreased use of most compounds used to treat plant disease, but growers have rapidly adopted recently introduced "conventional" compounds and there is very limited use of microbial biocontrol agents to control plant disease.
Abstract: ▪ Abstract We used the California Pesticide Use Reports to study use of fungicides, bactericides, fumigants, and selected insecticides, primarily for vegetable, fruit, and nut production in California from 1993 to 2000. There were no obvious trends in decreased use of most compounds used to treat plant disease. However, growers have rapidly adopted recently introduced “conventional” compounds. There is very limited use of microbial biocontrol agents to control plant disease and no indication of an increase. We used case studies to explore the potential of different strategies to reduce pesticide use or risk. There have been reductions in use of organophosphate insecticides, largely by substitution with pyrethroids. Theoretically, replacement of “calendar spray” pesticide programs with “environmentally driven” programs could reduce pesticide use in years with lower disease pressure, but this assumes that the majority of growers currently use a “calendar spray” program and that growers who use less than rec...