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  • Durable resistance of crops to disease: a Darwinian perspective.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 2015-06-17
    James K M Brown

    This review takes an evolutionary view of breeding crops for durable resistance to disease. An understanding of coevolution between hosts and parasites leads to predictors of potentially durable resistance, such as corresponding virulence having a high fitness cost to the pathogen or resistance being common in natural populations. High partial resistance can also promote durability. Whether or not resistance is actually durable, however, depends on ecological and epidemiological processes that stabilize genetic polymorphism, many of which are absent from intensive agriculture. There continues to be no biological, genetic, or economic model for durable resistance. The analogy between plant breeding and natural selection indicates that the basic requirements are genetic variation in potentially durable resistance, effective and consistent selection for resistance, and an efficient breeding process in which trials of disease resistance are integrated with other traits. Knowledge about genetics and mechanisms can support breeding for durable resistance once these fundamentals are in place.

    更新日期:2019-11-01
  • Plant-parasite coevolution: bridging the gap between genetics and ecology.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 2011-04-26
    James K M Brown,Aurélien Tellier

    We review current ideas about coevolution of plants and parasites, particularly processes that generate genetic diversity. Frequencies of host resistance and parasite virulence alleles that interact in gene-for-gene (GFG) relationships coevolve in the familiar boom-and-bust cycle, in which resistance is selected when virulence is rare, and virulence is selected when resistance is common. The cycle can result in stable polymorphism when diverse ecological and epidemiological factors cause negative direct frequency-dependent selection (ndFDS) on host resistance, parasite virulence, or both, such that the benefit of a trait to fitness declines as its frequency increases. Polymorphism can also be stabilized by overdominance, when heterozygous hosts have greater resistance than homozygotes to diverse pathogens. Genetic diversity can also persist in the form of statistical polymorphism, sustained by random processes acting on gene frequencies and population size. Stable polymorphism allows alleles to be long-lived and genetic variation to be detectable in natural populations. In agriculture, many of the factors promoting stability in host-parasite interactions have been lost, leading to arms races of host defenses and parasite effectors.

    更新日期:2019-11-01
  • Companion cropping to manage parasitic plants.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 2010-05-01
    John A Pickett,Mary L Hamilton,Antony M Hooper,Zeyaur R Khan,Charles A O Midega

    Parasitic plants, through a range of infestation strategies, can attack crop plants and thereby require management. Because such problems often occur in resource-poor farming systems, companion cropping to manage parasitic plants is an appropriate approach. Many examples of companion cropping for this purpose have been reported, but the use of cattle forage legumes in the genus Desmodium as intercrops has been shown to be particularly successful in controlling the parasitic witchweeds (Striga spp.) that afflict approximately one quarter of sub-Saharan African cereal production. Through the use of this example, the development of effective companion crops is described, together with developments toward widespread adoption and understanding the underlying mechanisms, both for sustainability and ensuring food security, and also for exploitation beyond the cropping systems described here.

    更新日期:2019-11-01
  • Epidemiological models for invasion and persistence of pathogens.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 2008-08-06
    Christopher A Gilligan,Frank van den Bosch

    Motivated by questions such as "Why do some diseases take off, while others die out?" and "How can we optimize the deployment of control methods," we introduce simple epidemiological concepts for the invasion and persistence of plant pathogens. An overarching modeling framework is then presented that can be used to analyze disease invasion and persistence at a range of scales from the microscopic to the regional. Criteria for invasion and persistence are introduced, initially for simple models of epidemics, and then for models with greater biological realism. Some ways in which epidemiological models are used to identify optimal strategies for the control of disease are discussed. Particular attention is given to the spatial structure of host populations and to the role of chance events in determining invasion and persistence of plant pathogens. Finally, three brief case studies are used to illustrate the practical applications of epidemiological theory to understand invasion and persistence of plant pathogens. These comprise long-term predictions for the persistence and control of Dutch elm disease; identification of methods to manage the spread of rhizomania on sugar beet in the U.K. by matching the scale of control with the spatial and temporal scales of the disease; and analysis of evolutionary change in virus control to identify risks of inadvertent selection for damaging virus strains.

    更新日期:2019-11-01
  • Models of fungicide resistance dynamics.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 2008-08-06
    Frank van den Bosch,Christopher A Gilligan

    We describe two classes of models used for fungicide and antibiotic resistance dynamics. One class assumes that the density of the pathogen (or severity of the disease caused by the pathogen) has no feedback effects on the rate at which new infections arise. The second class does not make this assumption. A quantitative relationship between these two classes is derived. We then discuss the two sets of assumptions made in the literature about initial conditions: either both the fungicide-sensitive strain and the -resistant strain are initially at low density, or the sensitive strain is resident at nonlow density and the resistant strain is initially at low density. We show that models of fungicide resistance dynamics with and without density-dependent feedback give contrasting predictions on the effects of pathogen life-cycle parameters and the effects of the fungicide (dose, frequency, use of mixtures, spatial usage restrictions) on the evolution, invasion, and spread of fungicide resistance. We further show that the evaluation of a resistance management strategy requires a very precise definition of what constitutes a good strategy.

    更新日期:2019-11-01
  • Diverse targets of phytoplasma effectors: from plant development to defense against insects.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 2011-08-16
    Akiko Sugio,Allyson M MacLean,Heather N Kingdom,Victoria M Grieve,R Manimekalai,Saskia A Hogenhout

    Phytoplasma research begins to bloom (75). Indeed, this review shows that substantial progress has been made with the identification of phytoplasma effectors that alter flower development, induce witches' broom, affect leaf shape, and modify plant-insect interactions. Phytoplasmas have a unique life cycle among pathogens, as they invade organisms of two distinct kingdoms, namely plants (Plantae) and insects (Animalia), and replicate intracellularly in both. Phytoplasmas release effectors into host cells of plants and insects to target host molecules, and in plants these effectors unload from the phloem to access distal tissues and alter basic developmental processes. The effectors provide phytoplasmas with a fitness advantage by modulating their plant and insect hosts. We expect that further research on the functional characterization of phytoplasma effectors will generate new knowledge that is relevant to fundamental aspects of plant sciences and entomology, and for agriculture by improving yields of crops affected by phytoplasma diseases.

    更新日期:2019-11-01
  • Chemical biology of multi-host/pathogen interactions: chemical perception and metabolic complementation.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 2004-07-31
    Andrew G Palmer,Rong Gao,Justin Maresh,W Kaya Erbil,David G Lynn

    The xenognostic mechanisms of two multi-host pathogens, the causative agent of crown gall tumors Agrobacterium tumefaciens and the parasitic plant Striga asiatica, are compared. Both organisms are general plant pathogens and require similar information prior to host commitment. Two mechanistic strategies, chemical perception and metabolic complementation, are used to ensure successful host commitment. The critical reactions at host-parasite contact are proton and electron transfer events. Such strategies may be common among multi-host pathogens.

    更新日期:2019-11-01
  • Plant virus satellite and defective interfering RNAs: new paradigms for a new century.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 2004-07-31
    Anne E Simon,Marilyn J Roossinck,Zoltán Havelda

    Although many subviral RNAs reduce or intensify disease symptoms caused by the helper virus, only recently have clues concerning the mechanism of disease modulation been revealed. New models for DI RNA-mediated reduction in helper virus levels and symptom attenuation include DI RNA enhancement of posttranscriptional gene silencing (PTGS), which is an antiviral defense mechanism in plants. Symptom enhancement by the satRNA of Cucumber mosaic virus is caused by minus-strand induction of the programmed cell death pathway. In contrast, symptom enhancement by satC of Turnip crinkle virus is due to satC interference with virion formation, leading to increased levels of free coat protein, which is the viral suppressor of PTGS. Mutualism between satRNA and helper virus can be seen for the satRNA of Groundnut rosette virus, which contributes to the virus by allowing virion assembly. These novel findings are leading to re-evaluation of the relationships between subviral RNAs, helper viruses, and hosts.

    更新日期:2019-11-01
  • Type III secretion system effector proteins: double agents in bacterial disease and plant defense.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 2004-07-31
    James R Alfano,Alan Collmer

    Many phytopathogenic bacteria inject virulence effector proteins into plant cells via a Hrp type III secretion system (TTSS). Without the TTSS, these pathogens cannot defeat basal defenses, grow in plants, produce disease lesions in hosts, or elicit the hypersensitive response (HR) in nonhosts. Pathogen genome projects employing bioinformatic methods to identify TTSS Hrp regulon promoters and TTSS pathway targeting signals suggest that phytopathogenic Pseudomonas, Xanthomonas, and Ralstonia spp. harbor large arsenals of effectors. The Hrp TTSS employs customized cytoplasmic chaperones, conserved export components in the bacterial envelope (also used by the TTSS of animal pathogens), and a more specialized set of TTSS-secreted proteins to deliver effectors across the plant cell wall and plasma membrane. Many effectors can act as molecular double agents that betray the pathogen to plant defenses in some interactions and suppress host defenses in others. Investigations of the functions of effectors within plant cells have demonstrated the plasma membrane and nucleus as subcellular sites for several effectors, revealed some effectors to possess cysteine protease or protein tyrosine phosphatase activity, and provided new clues to the coevolution of bacterium-plant interactions.

    更新日期:2019-11-01
  • Integrated approaches for detection of plant pathogenic bacteria and diagnosis of bacterial diseases.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 2004-07-31
    Anne M Alvarez

    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.

    更新日期:2019-11-01
  • Biological control of chestnut blight with hypovirulence: a critical analysis.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 2004-07-31
    Michael G Milgroom,Paolo Cortesi

    Most hypovirulence in the chestnut blight fungus, Cryphonectria parasitica, is associated with infection by fungal viruses in the family Hypoviridae. Hypovirulence has controlled chestnut blight well in some locations in Europe and in Michigan in the United States. In contrast, with few exceptions, biological control has failed almost completely in eastern North America. Therapeutic treatment of individual cankers is successful in most cases, but the success of hypovirulence at the population level depends on the natural spread of viruses. Characteristics of three interacting trophic levels (virus, fungus, and tree), plus the environment, determine the success or failure of hypovirulence. Vegetative incompatibility restricts virus transmission, but this factor alone is a poor predictor of biological control. Any factor reducing the rate of chestnut blight epidemics enhances hypovirus invasion. Overall, however, not enough is understood about the epidemiological dynamics of this system to determine the crucial factors regulating the establishment of hypovirulence in chestnut forests.

    更新日期:2019-11-01
  • Microbial dynamics and interactions in the spermosphere.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 2004-07-31
    Eric B Nelson

    The spermosphere represents a short-lived, rapidly changing, and microbiologically dynamic zone of soil surrounding a germinating seed. It is analogous to the rhizosphere, being established largely by the carbon compounds released into the soil once the seed begins to hydrate. These seed exudations drive the microbial activities that take place in the spermosphere, many of which can have long-lasting impacts on plant growth and development as well as on plant health. In this review, I discuss the nature of the spermosphere habitat and the factors that give rise to its character, with emphasis on the types of microbial activities in the spermosphere that have important implications for disease development and biological disease control. This review, which represents the first comprehensive synthesis of the literature on spermosphere biology, is meant to illustrate the unique nature of the spermosphere and how studies of interactions in this habitat may serve as useful experimental models for testing hypotheses about plant-microbe associations and microbial ecology.

    更新日期:2019-11-01
  • Microbial diversity in soil: selection microbial populations by plant and soil type and implications for disease suppressiveness.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 2004-07-31
    P Garbeva,J A van Veen,J D van Elsas

    An increasing interest has emerged with respect to the importance of microbial diversity in soil habitats. The extent of the diversity of microorganisms in soil is seen to be critical to the maintenance of soil health and quality, as a wide range of microorganisms is involved in important soil functions. This review focuses on recent data relating how plant type, soil type, and soil management regime affect the microbial diversity of soil and the implication for the soil's disease suppressiveness. The two main drivers of soil microbial community structure, i.e., plant type and soil type, are thought to exert their function in a complex manner. We propose that the fact that in some situations the soil and in others the plant type is the key factor determining soil microbial diversity is related to the complexity of the microbial interactions in soil, including interactions between microorganisms and soil and microorganisms and plants. A conceptual framework, based on the relative strengths of the shaping forces exerted by plant and soil versus the ecological behavior of microorganisms, is proposed.

    更新日期:2019-11-01
  • Molecular aspects of plant virus transmission by olpidium and plasmodiophorid vectors.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 2004-07-31
    D'Ann Rochon,Kishore Kakani,Marjorie Robbins,Ron Reade

    The genome structures of a large number of viruses transmitted by olpidium and plasmodiophorid vectors have been determined. The viruses are highly diverse, belonging to 12 genera in at least 4 families. Plasmodiophorids are now classified as protists rather than true fungi. This finding, along with the recognition of the great variety of viruses transmitted by olpidium and plasmodiophorid vectors, will likely lead to an elaboration of the details of in vitro and in vivo transmission mechanisms. Recent progress in elucidating the interaction between Cucumber necrosis virus (CNV) and its zoospore vector suggests that specific sites on the capsid as well as on the zoospore are involved in transmission. Moreover, some features of CNV/zoospore attachment are similar to poliovirus/host cell interactions, suggesting evolutionary conservation of functional features of plant and animal virus capsids.

    更新日期:2019-11-01
  • Systemic acquired resistance.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 2004-07-31
    W E Durrant,X Dong

    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.

    更新日期:2019-11-01
  • Comparative genomics analyses of citrus-associated bacteria.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 2004-07-31
    Leandro M Moreira,Robson F de Souza,Nalvo F Almeida,João C Setubal,Julio Cezar F Oliveira,Luiz R Furlan,Jesus A Ferro,Ana C R da Silva

    Xylella fastidiosa 9a5c (XF-9a5c) and Xanthomonas axonopodis pv. citri (XAC) are bacteria that infect citrus plants. Sequencing of the genomes of these strains is complete and comparative analyses are now under way with the genomes of other bacteria of the same genera. In this review, we present an overview of this comparative genomic work. We also present a detailed genomic comparison between XF-9a5a and XAC. Based on this analysis, genes and operons were identified that might be relevant for adaptation to citrus. XAC has two copies of a type II secretion system, a large number of cell wall-degrading enzymes and sugar transporters, a complete energy metabolism, a whole set of avirulence genes associated with a type III secretion system, and a complete flagellar and chemotatic system. By contrast, XF-9a5c possesses more genes involved with type IV pili biosynthesis than does XAC, contains genes encoding for production of colicins, and has 4 copies of Type I restriction/modification system while XAC has only one.

    更新日期:2019-11-01
  • Management and resistance in wheat and barley to fusarium head blight.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 2004-07-31
    Guihua Bai,Gregory Shaner

    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.

    更新日期:2019-11-01
  • Lessons learned from the genome analysis of ralstonia solanacearum.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 2004-07-31
    Stéphane Genin,Christian Boucher

    Ralstonia solanacearum is a devastating plant pathogen with a global distribution and an unusually wide host range. This bacterium can also be free-living as a saprophyte in water or in the soil in the absence of host plants. The availability of the complete genome sequence from strain GMI1000 provided the basis for an integrative analysis of the molecular traits determining the adaptation of the bacterium to various environmental niches and pathogenicity toward plants. This review summarizes current knowledge and speculates on some key bacterial functions, including metabolic versatility, resistance to metals, complex and extensive systems for motility and attachment to external surfaces, and multiple protein secretion systems. Genome sequence analysis provides clues about the evolution of essential virulence genes such as those encoding the Type III secretion system and related pathogenicity effectors. It also provided insights into possible mechanisms contributing to the rapid adaptation of the bacterium to its environment in general and to its interaction with plants in particular.

    更新日期:2019-11-01
  • Evolution of plant parasitism among nematodes.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 2004-07-31
    J G Baldwin,S A Nadler,B J Adams

    Despite extraordinary diversity of free-living species, a comparatively small fraction of nematodes are parasites of plants. These parasites represent at least three disparate clades in the nematode tree of life, as inferred from rRNA sequences. Plant parasites share functional similarities regarding feeding, but many similarities in feeding structures result from convergent evolution and have fundamentally different developmental origins. Although Tylenchida rRNA phylogenies are not fully resolved, they strongly support convergent evolution of sedentary endoparasitism and plant nurse cells in cyst and root-knot nematodes. This result has critical implications for using model systems and genomics to identify and characterize parasitism genes for representatives of this clade. Phylogenetic studies reveal that plant parasites have rich and complex evolutionary histories that involve multiple transitions to plant parasitism and the possible use of genes obtained by horizontal transfer from prokaryotes. Developing a fuller understanding of plant parasitism will require integrating more comprehensive and resolved phylogenies with appropriate choices of model organisms and comparative evolutionary methods.

    更新日期:2019-11-01
  • Analysis of disease progress as a basis for evaluating disease management practices.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 2004-07-31
    M J Jeger

    The relationship between epidemiology and disease management is long-standing but sometimes tenuous. It may seem self-evident that improved understanding of epidemic processes will lead to more effective control practices but this remains a testable proposition rather than demonstrated reality. A wide range of models differing in mathematical sophistication and computational complexity has been proposed as a means of achieving a greater understanding of epidemiology and carrying this through to improved management. The potential exists to align these modeling approaches to evaluation of control practices and prediction of the consequent epidemic outcomes, but these have yet to make a major impact on practical disease management. For the immediate future simpler pragmatic approaches for analysis of disease progress, using nonlinear growth functions and/or integrated measures such as area under disease progress curves, will play a key role in informing tactical and strategic decisions on control treatments. These approaches have proved useful in describing control effectiveness and, in some cases, optimizing or changing control practices.

    更新日期:2019-11-01
  • Assessment and management of soil microbial community structure for disease suppression.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 2004-07-31
    Mark Mazzola

    Identification of the biological properties contributing to the function of suppressive soils is a necessary first step to the management of such systems for use in the control of soilborne diseases. The development and application of molecular methods for the characterization and monitoring of soil microbial properties will enable a more rapid and detailed assessment of the biological nature of soil suppressiveness. Although suppressive soils have provided a wealth of microbial resources that have subsequently been applied for the biological control of soilborne plant pathogens, the full functional capabilities of the phenomena have not been realized in production agricultural ecosystems. Cultural practices, such as the application of soil amendments, have the capacity to enhance disease suppression, though the biological modes of action may vary from that initially resident to the soil. Plants have a distinct impact on characteristics and activity of resident soil microbial communities, and therefore play an important role in determining the development of the disease-suppressive state. Likewise, plant genotype will modulate these same biological communities, and should be considered when developing strategies to exploit the potential of such a natural disease control system. Implementation of consistently effective practices to manage this resource in an economically and environmentally feasible manner will require more detailed investigation of these biologically complex systems and refinement of currently available methodologies.

    更新日期:2019-11-01
  • Tobacco mosaic virus: a model system for plant biology.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 2004-07-31
    Karen-Beth G Scholthof

    Tobacco mosaic virus (TMV) has had an illustrious history for more than 100 years, dating to Beijerinck's description of the mosaic disease of tobacco as a contagium vivum fluidum and the modern usage of the word "virus." Since then, TMV has been acknowledged as a preferred didactic model and a symbolic model to illuminate the essential features that define a virus. TMV additionally emerged as a prototypic model to investigate the biology of host plants, namely tobacco. TMV also exemplifies how a model system furthers novel, and often unexpected, developments in biology and virology. Today, TMV is used as a tool to study host-pathogen interactions and cellular trafficking, and as a technology to express valuable pharmaceutical proteins in tobacco. The history of TMV illustrates how pragmatic strategies to control an economically important disease of tobacco have had unexpected and transforming effects across platforms that impinge on plant health and public health.

    更新日期:2019-11-01
  • The accidental plant pathologist.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 2004-07-31
    Anne K Vidaver

    This article presents the experiences of a woman in academic plant pathology from the 1950s to today. Topics include the social climate for women in science, personal and professional developments and research discoveries, public policy issues in agriculture and biotechnology affecting plant pathology, and projections for the future of plant pathology.

    更新日期:2019-11-01
  • STATUS OF CACAO WITCHES' BROOM: biology, epidemiology, and management.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    L H Purdy,R A Schmidt

    Origins of Theobroma cacao and Crinipellis perniciosa occurred in the Amazon Basin region of South America, and their interaction, the witches' broom disease, was first described in the late 1700s. The 100 years of scientific investigations of witches' broom of cacao that began in the 1890s developed the present state of knowledge of the biology and epidemiology of witches' broom that are discussed. Recommended management to reduce the deleterious effects of witches' broom on cacao production include the use of phytosanitation (removal of diseased plant parts), applications of chemical fungicides, and the use of host resistance. At present, there is a paucity of resistant planting materials, and efforts to evaluate germplasm for resistance to witches' broom are described. Research topics to augment present knowledge about witches' broom of cacao are presented with the hope that disease management can be improved.

    更新日期:2019-11-01
  • RESISTANCE TO PHENYLAMIDE FUNGICIDES: a case study with phytophthora infestans involving mating type and race structure.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    U Gisi,Y Cohen

    Phenylamide-resistant isolates of Phytophthora infestans have gradually become an important part of populations in many countries. However, fungicide mixtures containing a phenylamide component are still an effective strategy for the control of late blight in potato and tomato. The proportion of phenylamide-resistant isolates fluctuates from year to year and within the season. Almost concurrent with the appearance of resistant isolates was the discovery of the A2 mating type of P. infestans in many European countries and in other parts of the world. However, no genetic correlation exists between resistance and mating type, and the proportion of A2 isolates in European populations remains small. Resistance to phenylamides became established in A1 populations before the appearance of A2 type. Resistant isolates express equal or greater fitness than sensitive isolates, but no correlation was detected between resistance and race structure. The continuous changes in P. infestans populations require careful adaptation of successful disease control programs.

    更新日期:2019-11-01
  • Changing options for the control of deciduous fruit tree diseases.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    T B Sutton

    The evolution of disease management programs for deciduous fruit trees in the United States over the past 50 years has been influenced by factors that include public concern over pesticide residues on fruit and in the environment, the development of resistance of many important tree pathogens to fungicides and bactericides, the loss of fungicide registrations and restrictions on their use due to concern for human health and the environment and/or marketing decisions by the manufacturers, and changes in cultural practices and marketing objectives. These factors have led to wider use of forecasting models and cultural controls, the development of resistance management strategies, and the introduction of new equipment and methods for pesticide application. These same factors will most likely continue to drive the fruit industry to adopt disease management programs that rely less on pesticides in the future.

    更新日期:2019-11-01
  • Breeding disease-resistant wheats for tropical highlands and lowlands.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    H J Dubin,S Rajaram

    Wheat is grown on about 10 million ha in the tropical highlands and lowlands of the world, where it is an important food source. Many farmers in these areas work under subsistence conditions. Wheat diseases in tropical regions can be severe and require significant efforts to control. For economic and environmental reasons, host plant resistance is the most appropriate and sustainable disease control method. We describe highland and lowland tropical wheat regions and discuss CIMMYT's breeding strategies, philosophies, and progress in developing resistance to the major diseases such as rusts, foliar blights, fusarium scab, BYD, and spot blotch. Additionally, we review the role of national wheat research programs and beneficial spillovers of our combined breeding efforts to other wheat production areas of the world.

    更新日期:2019-11-01
  • QTL mapping and quantitative disease resistance in plants.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    N D Young

    Quantitative trait locus (QTL) mapping is a highly effective approach for studying genetically complex forms of plant disease resistance. With QTL mapping, the roles of specific resistance loci can be described, race-specificity of partial resistance genes can be assessed, and interactions between resistance genes, plant development, and the environment can be analyzed. Outstanding examples include: quantitative resistance to the rice blast fungus, late blight of potato, gray leaf spot of maize, bacterial wilt of tomato, and the soybean cyst nematode. These studies provide insights into the number of quantitative resistance loci involved in complex disease resistance, epistatic and environmental interactions, race-specificity of partial resistance loci, interactions between pathogen biology, plant development and biochemistry, and the relationship between qualitative and quantitative loci. QTL mapping also provides a framework for marker-assisted selection of complex disease resistance characters and the positional cloning of partial resistance genes.

    更新日期:2019-11-01
  • Recombination and the multilocus structure of fungal populations.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    M G Milgroom

    This review examines the relationship between recombination and the multilocus structure of populations. This discussion of population structure is based on the pattern of genetic variation within populations, especially the frequencies of multilocus genotypes, which can be used for making inferences about recombination. Three questions are addressed: Is population structure consistent with a random mating hypothesis? Is there evidence for recombination? How frequently does recombination occur?

    更新日期:2019-11-01
  • Genetics of resistance to wheat leaf rust.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    J A Kolmer

    Leaf rust (caused by Puccinia recondita f. sp. tritici) is the most widespread and regularly occurring rust on wheat. Genetic resistance is the most economical method of reducing yield losses due to leaf rust. To date, 46 leaf rust resistance genes have been designated and mapped in wheat. Resistance gene expression is dependent on the genetics of host-parasite interaction, temperature conditions, plant developmental stage, and interaction between resistance genes with suppressors or other resistance genes in the wheat genomes. Genes expressed in seedling plants have not provided long-lasting effective leaf rust resistance. Adult-plant resistance genes Lr13 and Lr34 singly and together have provided the most durable resistance to leaf rust in wheat throughout the world. Continued efforts to isolate, characterize, and map leaf rust resistance genes is essential given the ability of the leaf rust fungus to overcome deployed resistance genes.

    更新日期:2019-11-01
  • Pathogen quiescence in postharvest diseases.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    D Prusky

    This chapter examines the quiescence period during different stages of fungal attack of postharvest pathogens: quiescence during spore germination and initial hyphal development, during and after appressorium formation, and quiescence of germinated appressorium and subcuticular hyphae. The different mechanisms for quiescence are reviewed: factors affecting quiescence of germinated spores, appressoria formation and germination, and fungal colonization. Special emphasis is given to mechanisms of quiescence involving fungal colonization: 1. the pathogen's nutritional requirements, 2. preformed antifungal compounds, 3. the elicitation of phytoalexins and preformed compounds, and 4. the activation of factors in fungal pathogenicity.

    更新日期:2019-11-01
  • Microbial elicitors and their receptors in plants.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    M G Hahn

    Elicitors are molecules that stimulate any of a number of defense responses in plants. Research over the past decade has focused on the mechanisms by which plant cells perceive and transduce these biological signals to activate defense responses. Of particular interest has been the identification of specific elicitor-binding proteins that might function as physiological receptors in the signal transduction cascade. The existence of specific high-affinity binding sites has been demonstrated for oligosaccharide, glycopeptide, and peptide elicitors, and candidate elicitor-binding proteins have been identified for several of them. The properties of these binding sites/proteins are consistent with those expected of physiologically important receptors, although experimental verification of the role of these binding proteins as receptors has not yet been obtained. The purification and characterization of specific elicitor-binding proteins is essential for a detailed understanding of the molecular basis for the signal exchange between plant hosts and microbial pathogens that leads to activation of host defenses.

    更新日期:2019-11-01
  • Morphogenesis and mechanisms of penetration by plant pathogenic fungi.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    K Mendgen,M Hahn,H Deising

    Infection structures of phytopathogenic fungi are modified hyphae specialized for the invasion of plant tissues. Initial events are adhesion to the cuticle and directed growth of the germ tube on the plant surface. At the site of penetration, appressoria are often formed that may have melanized walls and develop high turgor pressure to support the penetration process. The penetration hypha accumulates components of the cytoskeleton in the tip and secretes a variety of cell wall-degrading enzymes in a highly regulated fashion in order to penetrate the cuticle and the plant cell wall. This article reviews recent papers on the cytology, physiology, and molecular biology of the penetration process.

    更新日期:2019-11-01
  • Ozone and plant health.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    H Sandermann

    Phytotoxic effects of ozone are described with emphasis on secondary plant metabolism. Numerous ozone-induced genes, enzymes and stress metabolites of antioxidative and phytopathological defense reactions have been discovered for herbaceous plants and forest tree species. Ozone induces reactions normally elicited by viral and microbial pathogens. The molecular basis (receptors, signal chains) for induction by ozone remains to be elucidated. The induced stress reactions seem to change plant predisposition to either enhanced tolerance or susceptibility for a second stressor. The following topics are discussed: ozone and biotic disease, the role of ozone on field sites and ozone limit values.

    更新日期:2019-11-01
  • Root system regulation of whole plant growth.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    R M Aiken,A J Smucker

    New evidence confirms earlier postulates that root signals to shoots, including abscisic acid, nitrate flux, and cytokinins, modify whole plant growth processes including leaf expansion, stomatal behavior, and biosynthesis of photosynthetic enzymes. Root signals are thought to reflect soil water, nutrient, and mechanical attributes, as sensed by roots. Meristematic activities in root tips initiate changes in root architecture, modifying the soil volume subject to root uptake, and may provide multiple sensory and signaling capabilities. Knowledge of root signals regulating whole plant growth processes suggests new analytical and experimental tools for integrated analysis of plant phasic development, optimal growth, and ecological fitness.

    更新日期:2019-11-01
  • Plant virus gene vectors for transient expression of foreign proteins in plants.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    H B Scholthof,K B Scholthof,A O Jackson

    The development of plant virus gene vectors for expression of foreign genes in plants provides attractive biotechnological tools to complement conventional breeding and transgenic methodology. The benefits of virus-based transient RNA and DNA replicons versus transgenic gene expression include rapid and convenient engineering coupled with flexibility for expeditious application in various plant species. These characteristics are especially advantageous when very high levels of gene expression are desired within a short time, although instability of the foreign gene in the viral genome can present some problems. The strategies that have been tested for foreign gene expression in various virus-based vectors include gene replacement, gene insertion, epitope presentation, use of virus controlled gene expression cassettes, and complementation. Recent reports of the utilization of virus vectors for foreign gene expression in fundamental research and biotechnology applications are discussed.

    更新日期:2019-11-01
  • Molecular biology of rice tungro viruses.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    R Hull

    Rice tungro, the most important virus disease of rice in South and Southeast Asia, is caused by a complex of two viruses, rice tungro bacilliform virus (RTBV) and rice tungro spherical virus (RTSV). RTBV is a plant pararetrovirus with bacilliform particles, the structure of which is based on T = 3 icosahedral symmetry cut across the threefold axis.The particles encapsidate a circular double-stranded DNA of 8 kbp that encodes four proteins. The current information on the properties, functions, and expression of these proteins is discussed, as is the evidence for replication by reverse transcription. Two major strains of RTBV have been recognized, one from the Indian subcontinent and the other from Southeast Asia. RTSV particles contain a single-stranded RNA genome of 12 kb that encodes a large polyprotein and possibly one or two smaller proteins. The properties and processing of the polyprotein are described and the resemblance to picornaviruses noted.

    更新日期:2019-11-01
  • Biology and epidemiology of rice viruses.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    H Hibino

    The 15 known viruses that occur in rice are rice black-streaked dwarf, rice bunchy stunt, rice dwarf, rice gall dwarf, rice giallume, rice grassy stunt, rice hoja blanca, rice necrosis mosaic, rice ragged stunt, rice stripe necrosis, rice stripe, rice transitory yellowing, rice tungro bacilliform, rice tungro spherical, and rice yellow mottle viruses. This paper describes their geographical distribution, relation to vectors, infection cycles, field dispersal, and development, and lists recorded outbreaks of the viruses. Many rice viruses have become serious problems since rice cultivation has been intensified. Double-cropping of rice using improved, photo-insensitive cultivars of short growth duration has significantly influenced the incidence of these viruses.

    更新日期:2019-11-01
  • Helper-dependent vector transmission of plant viruses.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    T P Pirone,S Blanc

    A variety of noncirculatively transmitted viruses have evolved a vector transmission strategy that involves, in addition to virions, virus-encoded proteins that are not constituents of virions. These "helpers" and the genes encoding them have been characterized for viruses in the genera Potyvirus and Caulimovirus. Several lines of evidence support the hypothesis that these helpers act by mediating retention of virions in regions of the vector's alimentary tract from which they subsequently can be egested to initiate an infection. The possible advantage this convergently evolved strategy could confer to noncirculatively transmitted virus quasispecies is discussed.

    更新日期:2019-11-01
  • Nematode management in sustainable and subsistence agriculture.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    J Bridge

    In small-scale, subsistence agriculture in the tropics and the subtropics, traditional farming practices have evolved that provide a sustainable means of reducing the incidence and damage caused by pests including nematodes. Other newer, cultural and low-input practices can also be successfully introduced in small-scale farming. In sustainable and subsistence farming systems, nematodes and some other pests can be managed by integrating different farming practices into four strategies: preventing the introduction and spread of nematodes; using direct, nonchemical, cultural and physical control methods; encouraging naturally occurring biological control agents; and maintaining or enhancing the biodiversity inherent in multiple cropping and multiple cultivar traditional farming systems to increase the available resistance or tolerance to nematodes.

    更新日期:2019-11-01
  • Chemoreception in plant parasitic nematodes.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    R N Perry

    The role and functioning of the anterior chemosensory organs of plant parasitic nematodes is examined, with particular emphasis on the amphids. The morphology of the amphids is discussed primarily in the context of the changes in the ultrastructure associated with different life stages. The involvement of amphidial secretions in chemoreception and the behavioral and electrophysiological analyses of nematode responses to semiochemicals are discussed with special reference to research on sex pheromones. These research techniques, combined with the use of lectins and antibodies, provide information on nematode sensilla that may lead to novel control strategies for economically important plant parasitic nematodes based on perturbing nematode sensory perception to prevent host or mate location.

    更新日期:2019-11-01
  • Bacterial avirulence genes.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    J E Leach,F F White

    Although more than 30 bacterial avirulence genes have been cloned and characterized, the function of the gene products in the elictitation of resistance is unknown in all cases but one. The product of avrD from Pseudomonas syringae pv. glycinea likely functions indirectly to elicit resistance in soybean, that is, evidence suggests the gene product is an enzyme involved in elicitor production. In most if not all cases, bacterial avirulence gene function is dependent on interactions with the hypersensitive response and pathogenicity (hrp) genes. Many hrp genes are similar to genes involved in delivery of pathogenicity factors in mammalian bacterial pathogens. Thus, analogies between mammalian and plant pathogens may provide needed clues to elucidate how virulence gene products control induction of resistance.

    更新日期:2019-11-01
  • Fastidious xylem-limited bacterial plant pathogens.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    A H Purcell,D L Hopkins

    Numerous bacteria have been isolated from within plants, and many reported from xylem, but only three species of xylem-limited bacteria (XLB) that are fastidious in cultural requirements, are plant pathogens, and exclusively occupy xylem, have been well characterized. Two XLB, Xylella fastidiosa and Pseudomonas syzygii, are transmitted by sucking insects that feed on xylem sap but are not transmitted mechanically from plant to plant. In contrast, Clavibacter xyli is mechanically transmitted to plants by cutting tools. All of these XLB occupy a highly specialized yet diverse ecological niche: the water-conducting systems of an extremely wide range of plant hosts. A variety of detection methods are available as diagnostic aids; each method has advantages and disadvantages; no single method is best for all uses. Molecular and genetic comparisons of strains of XLB lag behind progress being made for many other plant-pathogenic bacteria, but such studies are needed to answer important questions: (a) How do XLB move from cell to cell within plants? (b) What are the physiological and genetic bases of plant host specificity for XLB? (c) Why are only xylem-feeding specialists vectors of X. fastidiosa (and probably P. syzygii), when many leafhoppers feed regularly (but not continuously) on xylem?

    更新日期:2019-11-01
  • EPICHLOE SPECIES: fungal symbionts of grasses.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    C L Schardl

    Epichloë species and their asexual descendants (Acremonium endophytes) are fungal symbionts of C3 grasses that span the symbiotic continuum from antagonism to mutualism depending on the relative importance, respectively, of horizontal transmission of sexual spores versus vertical clonal transmission in healthy grass seeds. At least seven sexual Epichloë species are identifiable by mating tests, and many asexual genotypes are interspecific hybrids. Benefits conferred by the symbionts on host plants include protection from biotic factors and abiotic stresses such as drought. Four classes of beneficial alkaloids are associated with the symbionts: ergot alkaloids, indolediterpenes (lolitrems), peramine, and saturated aminopyrrolizidines (lolines). These alkaloids protect host plants from insect and vertebrate herbivores, including livestock. Genetic engineering of the fungal symbionts as more suitable biological protectants for forage grasses requires identification of fungal genes for alkaloid biosynthesis, and DNA-mediated transformation of the fungi.

    更新日期:2019-11-01
  • Fungal transmission of plant viruses.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    R N Campbell

    Thirty soilborne viruses or virus-like agents are transmitted by five species of fungal vectors. Ten polyhedral viruses, of which nine are in the family Tombusviridae, are acquired in the in vitro manner and do not occur within the resting spores of their vectors, Olpidium brassicae and O. bornovanus. Fungal vectors for other viruses in the family should be sought even though tombusviruses are reputed to be soil transmitted without a vector. Eighteen rod-shaped viruses belonging to the furo- and bymovirus groups and to an unclassified group are acquired in the in vivo manner and survive within the resting spores of their vector, O. brassicae, Polymyxa graminis, P. betae, and Spongospora subterranea. The viral coat protein has an essential role in in vitro transmission. With in vivo transmission a site in the coat protein-read through protein (CP-RT) of beet necrotic yellow vein furovirus determines vector transmissibility as does a site in a similar 98-kDa polyprotein of barley mild mosaic bymovirus. The mechanisms by which virions move (or are moved) into and out of the protoplasm of zoospores or of thalli needs study.

    更新日期:2019-11-01
  • DWARF BUNT: politics, identification, and biology.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    D E Mathre

    Dwarf bunt is a disease of wheat caused by the smut fungus Tilletia controversa Kuhn. Winter wheat (Triticum aestivum L.) is the primary host of economic significance. Although the total acreage affected by dwarf bunt is small relative to total wheat production worldwide, the disease has assumed attention disproportionate to its economic impact because it has become a matter of contention in world trade in cereals. This review describes the political and economic issues underlying the study and identification of T. controversa.

    更新日期:2019-11-01
  • The role of plant clinics in plant disease diagnosis and education in developing countries.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    R Ausher,I S Ben-Ze'ev,R Black

    The scarcity of literature in the realm of plant clinics operating in the developing world brought us to the decision to perform a survey in non-OECD countries in Africa, Asia and Oceania, Latin America and the Caribbean, and in central and southern Europe. Forty-one completed questionnaires that refer to 79 plant clinics were returned. The best-equipped clinics are operated by the international research bodies. By and large, this review shows that considerable progress has been achieved in the physical development of plant clinics in developing countries and in staffing them with well-trained personnel. Not surprisingly, however, many inadequacies and inconsistencies still need to be addressed before clinics can fully play their part in providing plant protection services to their clients. Success and constraining indicators in the diagnostic performance of the clinics are identified. A model of the'ideal plant clinic' is suggested.

    更新日期:2019-11-01
  • The Red Queen Hypothesis and plant/pathogen interactions.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    K Clay,P X Kover

    The Red Queen Hypothesis (RQH) explains how pathogens may maintain sexual reproduction in hosts. It assumes that parasites become specialized on common host genotypes, reducing their fitness. Such frequency-dependent selection favors sexual reproduction in host populations. Necessary conditions are that resistance and virulence are genotype specific so that host genotype frequencies respond to changes in pathogen genotype frequencies, and vice versa. Empirical evidence on the genetic basis of disease, variation in resistance and virulence, and patterns of infection in sexual and asexual plants support certain features of the hypothesis. However, gene-for-gene interactions are generally not consistent with the RQH because they do not result in cycling of gene frequencies, unlike a matching allele mechanism. A conclusion of whether the RQH can explain the maintenance of sexual reproduction cannot be reached at present. Nevertheless, the RQH theory has shed light on many aspects of plant/pathogen interactions important for reducing pathogen damage in agricultural systems.

    更新日期:2019-11-01
  • Dr. Gotthold Steiner (1886-1961): versatile nematologist.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    R P Esser

    Swiss-born Dr. Gotthold Steiner was a pioneer in formulating the discipline of nematology. He worked with the American nematologist NA Cobb and together they were responsible for acceptance of the concept of nematode phytoparasites. Steiner had special expertise in anatomy, morphology, phytonematology, marine nematodes, nutrition, mermithids, and selected invertebrate taxa. He authored 191 scientific papers, established the ubiquitous phytoparasitic genus Helicotylenchus, described the pinewood nematode, and did significant work with three important economic pests, Ditylenchus dipsaci, Heterodera rostochiensis, and H. schachtii. He was responsible for introducing training programs in nematology in USDA laboratories.

    更新日期:2019-11-01
  • Helen Hart, remarkable plant pathologist (1900-1971).
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    R D Wilcoxson

    Helen Hart was a Professor of Plant Pathology at the University of Minnesota from 1924 until retirement in 1966. Born in Janeville, Wisconsin, she died at Grants Pass, Oregon. Her scholarly research concentrated on wheat stem rust to understand host pathogen relationships and to develop rust-resistant cultivars. She did not teach formal courses but was heavily involved in making seminars a vital part of instruction, in teaching languages needed for graduate studies, and as an informal advisor for most rust research theses. She had common sense, excellent scientific judgment, and sound instincts on personnel matters that served the department well. A talented science writer, Hart served as editor of hundreds of theses and departmental manuscripts for publication. Her writing and editing skills were used as associate editor of Phytopathology for two years and as editor-in-chief from 1944-1951. A strong advocate of The American Phytopathological Society, Helen Hart served on Council for 12 years and as President in 1956. Helen Hart was a great professional scientist who had a far-reaching impact on plant pathology during the twentieth century.

    更新日期:2019-11-01
  • PLANT PATHOLOGY: a discipline at a crossroads.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1996-01-01
    A R Weinhold

    The Department of Plant Pathology at the University of California at Berkeley was destroyed as a consequence of a contentious reorganization. The circumstances that led to the reorganization provide some insight into the challenges facing the discipline of plant pathology. The underlying basis for plant pathology as a science is to address problems of plant disease. This requires a balance between disciplinary and problem-solving research and a continuum from achieving fundamental advances in knowledge to the development and implementation of problem-solving approaches. Changes in colleges and universities have placed extreme stress on this essential structure. The dilemma that must be addressed is how to reestablish the problem-solving continuum where it has been broken and strengthen it where it has been weakened. Plants are essential for life, and they will always be affected by disease. The understanding and management of these diseases is the responsibility and the challenge of plant pathology today and in the future.

    更新日期:2019-11-01
  • Role of plant pathology in integrated pest management.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1997-01-01
    B J Jacobsen

    Integrated Pest Management (IPM) is a paradigm that is widely adopted by all pest control disciplines but whose early definitions and philosophical basis belong to entomologists. Plant pathology research and extension work has historically emphasized integration of several control strategies and fits both historical and modern definitions of IPM. While the term IPM has been used only sparingly in the phytopathology literature, the integrated disease management strategies emphasized are now considered to be at the forefront of ecologically based or biointensive pest management. While IPM is broadly endorsed by crop protection disciplines, farmers, other agriculturalists, and consumers, the potential for Integrated Pest Management has not been fully realized. Most IPM programs reflect a package of tools and decision aids for individual crop insect, weed, nematode, and plant disease management. IPM programs that integrate all types of pests with the agroecosystem, crop growth and loss models still await the formation of interdisciplinary teams focusing on growers needs. Lack of funding for both discipline and interdisciplinary developmental research and implementation is responsible for the paucity of comprehensive IPM programs for the majority of the U.S. crop acreage. This review explores the origins and evolution of the IPM paradigm and reviews efforts to achieve the body of knowledge and implementation structure to achieve IPM's full potential.

    更新日期:2019-11-01
  • Rationale and perspectives on the development of fungicides.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1997-01-01
    S C Knight,V M Anthony,A M Brady,A J Greenland,S P Heaney,D C Murray,K A Powell,M A Schulz,C A Spinks,P A Worthington,D Youle

    Fungicides continue to be essential for the effective control of plant diseases. New classes of fungicides with novel modes of action are being developed in the 1990s. These include the strobilurins, phenylpyrroles, anilinopyrimidines, phenoxyquinolines, and compounds that trigger defense mechanisms in the plant. For the foreseeable future, new toxophores will be identified through a process of random screening, with natural products representing a rich source of fungicide leads. Progress is being made in the development of high-throughput screens comprised of target enzyme sites or cell-based assays; these techniques will improve the probability of discovery. Following the identification of suitable leads, biorational design is used to optimize specific properties. In vivo glasshouse screens and field trials are expected to remain the dominant methods for characterizing new compounds. Low toxicity to humans and wildlife, low environmental impact, low residues in food, and compatibility with integrated pest management (IPM) programs are increasingly important considerations in the selection of fungicides for development.

    更新日期:2019-11-01
  • Microbial population dynamics on leaves.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1997-01-01
    L L Kinkel

    Microbial population dynamics on leaves in time and space are a function of immigration, emigration, growth, and death. Insight into the relative significance of each population process to the generation of specific dynamics for individual microorganisms is necessary to understanding the ecology and life history strategy of the microorganism and to developing effective control strategies. Additionally, information on the significance of within-leaf versus extra-leaf processes to the generation of phyllosphere dynamics is important to determining the range of spatial scales over which a population should be studied. Unfortunately, such information is difficult to obtain due to the lack of effective methodologies for distinguishing these processes within phyllosphere populations. Future research efforts should focus on the quantification of immigration, emigration, growth, and death relative to the population dynamics of phyllosphere microorganisms.

    更新日期:2019-11-01
  • Anticipatory breeding for resistance to rust diseases in wheat.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1997-01-01
    R A McIntosh,G N Brown

    Anticipatory resistance breeding is the process of predicting future pathotypes and producing resistant germplasm to avert future losses. It is made possible by a national pathotype surveillance program and knowledge that new pathotypes arise predominantly from mutation in existing pathotypes. This is supported by genetic analyses to catalogue the identity and distribution of resistance genes in current cultivars. A national germplasm enhancement program ensuring that both currently effective and potentially new sources of resistance are available in a wide range of adapted genotypes enables rapid cultivar replacement before or soon after the occurrence of new pathotypes. The policy of recommending only rust-resistant cultivars in the more rust-prone areas has resulted in significant reductions in pathogen population size and variability. With increased and more rapid international human travel and transport, there is an increased threat of exotic pathotypes, the effects of which are more difficult to predict. As the frequency and magnitude of epidemics decline, public awareness programs will be required to achieve and maintain the use of rust resistance by the entire wheat industry.

    更新日期:2019-11-01
  • Advances in the molecular genetic analysis of the flax-flax rust interaction.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1997-01-01
    J Ellis,G Lawrence,M Ayliffe,P Anderson,N Collins,J Finnegan,D Frost,J Luck,T Pryor

    The L6 and M rust-resistance genes, representing two of the five rust-resistance gene loci in flax (Linum usitatissimum), have been cloned. The molecular data are fully consistent with earlier genetic data: the L locus is a single gene with multiple alleles expressing different rust resistance specificities, and the M locus is complex, containing an array of about 15 similar genes. Thus, while L6 and M resistance genes have 86% nucleotide identity, their locus structure is very different. These genes encode products belonging to the nucleotide binding site-leucine-rich repeat class of disease-resistance proteins. Analysis of alleles from the L locus and chimeric genes is providing evidence suggesting that important specificity determinants occur in the C-terminal half of the proteins, the region containing the leucine-rich repeats. The isolation and characterization of the rust (Melampsora lini) avirulence genes that correspond to the cloned rust-resistance genes is one of the major challenges remaining to the understanding of this system.

    更新日期:2019-11-01
  • Structure and evolution of the rp1 complex conferring rust resistance in maize.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1997-01-01
    S H Hulbert

    Genetic analyses of the rp1 rust resistance complex of maize have demonstrated that recombination plays a central role in the creation of genetic diversity at the locus. The generation of rp1 diversity is promoted by a high rate of intragenic recombination coupled with a tendency for genes in the complex to mispair in meiosis. Among the novel rp1 genes that have been identified include genes with novel race-specificities and genes conferring lesion mimic phenotypes. Recombinants have also been identified that confer partial resistance which is apparently non-race-specific and may be useful in controlling maize rusts in a durable manner.

    更新日期:2019-11-01
  • Systemic acquired resistance.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1997-01-01
    L Sticher,B Mauch-Mani,J P Métraux

    This paper examines induced resistance (SAR) in plants against various insect and pathogenic invaders. SAR confers quantitative protection against a broad spectrum of microorganisms in a manner comparable to immunization in mammals, although the underlying mechanisms differ. Discussed here are the molecular events underlying SAR: the mechanisms involved in SAR, including lignification and other structural barriers, pathogenesis-related proteins and their expression, and the signals for SAR including salicylic acid. Recent findings on the biological role of systemin, ethylene, jasmonates, and electrical signals are reviewed. Chemical activators of SAR comprise inorganic compounds, natural compounds, and synthetic compounds. Plants known to exhibit SAR and induced systemic resistance are listed.

    更新日期:2019-11-01
  • Signal pathways and appressorium morphogenesis.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1997-01-01
    R A Dean

    Fungal pathogens have evolved elaborate strategies to gain access to plant tissues. For many pathogens, following attachment of spores to the leaf surface, germ tubes emerge and grow across the surface, often in response to particular environmental cues and to a specific location. At an appropriate site, polar elongation of the germ tube ceases, the tip attaches to the surface and swells to form an appressorium, a uniquely organized infection structure. Following a period of maturation, a hypha then emerges at the plant interface and penetrates into the plant tissues. This chapter discusses recent developments that provide new insight into the molecular mechanism regulating induction and function of appressoria. Topics include attachment to the leaf surface; environmental cues that signal germ-tube growth and appressorium formation; mechanisms for sensing environmental cues; endogenous signaling pathways; and mechanisms of penetration from the appressorium.

    更新日期:2019-11-01
  • Mechanisms of plant virus evolution.
    Annu. Rev. Phytopathol. (IF 10.200) Pub Date : 1997-01-01
    M J Roossinck

    Plant viruses utilize several mechanisms to generate the large amount of genetic diversity found both within and between species. Plant RNA viruses and pararetroviruses probably have highly error prone replication mechanisms, that result in numerous mutations and a quasispecies nature. The plant DNA viruses also exhibit diversity, but the source of this is less clear. Plant viruses frequently use recombination and reassortment as driving forces in evolution, and, occasionally, other mechanisms such as gene duplication and overprinting. The amount of variation found in different species of plant viruses is remarkably different, even though there is no evidence that the mutation rate varies. The origin of plant viruses is uncertain, but several possible theories are proposed. The relationships between some plant and animal viruses suggests a common origin, possibly an insect virus. The propensity for rapid adaptation makes tracing the evolutionary history of viruses difficult, and long term control of virus disease nearly impossible, but it provides an excellent model system for studying general mechanisms of molecular evolution.

    更新日期:2019-11-01
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