scispace - formally typeset
Search or ask a question

Showing papers in "Annual Review of Phytopathology in 2015"


Journal ArticleDOI
TL;DR: This review covers recent advances in disclosing molecular mechanisms of priming, which include elevated levels of pattern-recognition receptors and dormant signaling enzymes, transcription factor HsfB1 activity, and alterations in chromatin state.
Abstract: When plants recognize potential opponents, invading pathogens, wound signals, or abiotic stress, they often switch to a primed state of enhanced defense. However, defense priming can also be induced by some natural or synthetic chemicals. In the primed state, plants respond to biotic and abiotic stress with faster and stronger activation of defense, and this is often linked to immunity and abiotic stress tolerance. This review covers recent advances in disclosing molecular mechanisms of priming. These include elevated levels of pattern-recognition receptors and dormant signaling enzymes, transcription factor HsfB1 activity, and alterations in chromatin state. They also comprise the identification of aspartyl-tRNA synthetase as a receptor of the priming activator β-aminobutyric acid. The article also illustrates the inheritance of priming, exemplifies the role of recently identified priming activators azelaic and pipecolic acid, elaborates on the similarity to defense priming in mammals, and discusses the ...

634 citations


Journal ArticleDOI
TL;DR: A three-step enrichment model for shifts in community structure from bulk soil toward roots, based on comparison of microbiome data for the different root-soil compartments and on knowledge of bacterial functions, is presented.
Abstract: Land plants interact with microbes primarily at roots. Despite the importance of root microbial communities for health and nutrient uptake, the current understanding of the complex plant-microbe interactions in the rhizosphere is still in its infancy. Roots provide different microhabitats at the soil-root interface: rhizosphere soil, rhizoplane, and endorhizosphere. We discuss technical aspects of their differentiation that are relevant for the functional analysis of their different microbiomes, and we assess PCR (polymerase chain reaction)-based methods to analyze plant-associated bacterial communities. Development of novel primers will allow a less biased and more quantitative view of these global hotspots of microbial activity. Based on comparison of microbiome data for the different root-soil compartments and on knowledge of bacterial functions, a three-step enrichment model for shifts in community structure from bulk soil toward roots is presented. To unravel how plants shape their microbiome, a major research field is likely to be the coupling of reductionist and molecular ecological approaches, particularly for specific plant genotypes and mutants, to clarify causal relationships in complex root communities.

457 citations


Journal ArticleDOI
TL;DR: An alternative view of plant innate immunity as a system that evolves to detect invasion is discussed, which accommodates the range from mutualistic to parasitic symbioses that plants form with diverse organisms, as well as the spectrum of ligands that the plant immune system perceives.
Abstract: Various conceptual models to describe the plant immune system have been presented. The most recent paradigm to gain wide acceptance in the field is often referred to as the zigzag model, which reconciles the previously formulated gene-for-gene hypothesis with the recognition of general elicitors in a single model. This review focuses on the limitations of the current paradigm of molecular plant-microbe interactions and how it too narrowly defines the plant immune system. As such, we discuss an alternative view of plant innate immunity as a system that evolves to detect invasion. This view accommodates the range from mutualistic to parasitic symbioses that plants form with diverse organisms, as well as the spectrum of ligands that the plant immune system perceives. Finally, how this view can contribute to the current practice of resistance breeding is discussed.

393 citations


Journal ArticleDOI
TL;DR: Current knowledge about host factors in the virus life cycle, particularly single-stranded, positive-sense RNA viruses, is summarized and future research directions are discussed.
Abstract: A successful infection by a plant virus results from the complex molecular interplay between the host plant and the invading virus. Thus, dissecting the molecular network of virus-host interactions advances the understanding of the viral infection process and may assist in the development of novel antiviral strategies. In the past decade, molecular identification and functional characterization of host factors in the virus life cycle, particularly single-stranded, positive-sense RNA viruses, have been a research focus in plant virology. As a result, a number of host factors have been identified. These host factors are implicated in all the major steps of the infection process. Some host factors are diverted for the viral genome translation, some are recruited to improvise the viral replicase complexes for genome multiplication, and others are components of transport complexes for cell-to-cell spread via plasmodesmata and systemic movement through the phloem. This review summarizes current knowledge about host factors and discusses future research directions.

240 citations


Journal ArticleDOI
TL;DR: This review takes an evolutionary view of breeding crops for durable resistance to disease, indicating 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.
Abstract: 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.

215 citations


Journal ArticleDOI
TL;DR: Recent advances in the understanding of the interactions between nematodes and nematophagous microorganisms are reviewed, with a focus on the molecular mechanisms by which nematophile microorganisms infect nem atodes and on the nematode defense against pathogenic attacks.
Abstract: Plant-parasitic nematodes cause significant damage to a broad range of vegetables and agricultural crops throughout the world. As the natural enemies of nematodes, nematophagous microorganisms offer a promising approach to control the nematode pests. Some of these microorganisms produce traps to capture and kill the worms from the outside. Others act as internal parasites to produce toxins and virulence factors to kill the nematodes from within. Understanding the molecular basis of microbe-nematode interactions provides crucial insights for developing effective biological control agents against plant-parasitic nematodes. Here, we review recent advances in our understanding of the interactions between nematodes and nematophagous microorganisms, with a focus on the molecular mechanisms by which nematophagous microorganisms infect nematodes and on the nematode defense against pathogenic attacks. We conclude by discussing several key areas for future research and development, including potential approaches to apply our recent understandings to develop effective biocontrol strategies.

181 citations


Journal ArticleDOI
TL;DR: The rapid spread of the Colorado potato beetle across Eurasia illustrates the importance of evolutionary adaptation, host distribution, and migration patterns in affecting the predictions of climate-based species distribution models.
Abstract: Crop pests and pathogens (CPPs) present a growing threat to food security and ecosystem management. The interactions between plants and their natural enemies are influenced by environmental conditions and thus global warming and climate change could affect CPP ranges and impact. Observations of changing CPP distributions over the twentieth century suggest that growing agricultural production and trade have been most important in disseminating CPPs, but there is some evidence for a latitudinal bias in range shifts that indicates a global warming signal. Species distribution models using climatic variables as drivers suggest that ranges will shift latitudinally in the future. The rapid spread of the Colorado potato beetle across Eurasia illustrates the importance of evolutionary adaptation, host distribution, and migration patterns in affecting the predictions of climate-based species distribution models. Understanding species range shifts in the framework of ecological niche theory may help to direct futur...

168 citations


Journal ArticleDOI
TL;DR: In this review, research and progress made over the past twenty years regarding soil health, sustainability, and soil health management practices, with an emphasis on their implications for and effects on plant disease and disease management strategies, are summarized.
Abstract: Soil health has been defined as the capacity of soil to function as a vital living system to sustain biological productivity, maintain environmental quality, and promote plant, animal, and human health. Building and maintaining soil health are essential to agricultural sustainability and ecosystem function. Management practices that promote soil health, including the use of crop rotations, cover crops and green manures, organic amendments, and conservation tillage, also have generally positive effects on the management of soilborne diseases through a number of potential mechanisms, including increasing soil microbial biomass, activity, and diversity, resulting in greater biological suppression of pathogens and diseases. However, there also may be particular disease issues associated with some soil health management practices. In this review, research and progress made over the past twenty years regarding soil health, sustainability, and soil health management practices, with an emphasis on their implications for and effects on plant disease and disease management strategies, are summarized.

166 citations


Journal ArticleDOI
TL;DR: The hypothesis that much of the QR to biotrophic filamentous pathogens is basal resistance, i.e., poor suppression of PAMP-triggered defense by effectors is proposed, and what role effectors play in suppressing defense or improving access to nutrients is discussed.
Abstract: Quantitative resistance (QR) refers to a resistance that is phenotypically incomplete and is based on the joined effect of several genes, each contributing quantitatively to the level of plant defense. Often, QR remains durably effective, which is the primary driver behind the interest in it. The various terms that are used to refer to QR, such as field resistance, adult plant resistance, and basal resistance, reflect the many properties attributed to it. In this article, we discuss aspects connected to those attributions, in particular the hypothesis that much of the QR to biotrophic filamentous pathogens is basal resistance, i.e., poor suppression of PAMP-triggered defense by effectors. We discuss what role effectors play in suppressing defense or improving access to nutrients. Based on the functions of the few plant proteins identified as involved in QR, vesicle trafficking and protein/metabolite transportation are likely to be common physiological processes relevant to QR.

163 citations


Journal ArticleDOI
TL;DR: A comparison of enrichment strategies reveals that full indexing of RNA and DNA viruses as well as viroids in a plant sample at single-nucleotide resolution is made possible by one NGS run of total small RNAs, followed by data mining with homology-dependent andhomology-independent computational algorithms.
Abstract: A fast, accurate, and full indexing of viruses and viroids in a sample for the inspection and quarantine services and disease management is desirable but was unrealistic until recently. This article reviews the rapid and exciting recent progress in the use of next-generation sequencing (NGS) technologies for the identification of viruses and viroids in plants. A total of four viroids/viroid-like RNAs and 49 new plant RNA and DNA viruses from 18 known or unassigned virus families have been identified from plants since 2009. A comparison of enrichment strategies reveals that full indexing of RNA and DNA viruses as well as viroids in a plant sample at single-nucleotide resolution is made possible by one NGS run of total small RNAs, followed by data mining with homology-dependent and homology-independent computational algorithms. Major challenges in the application of NGS technologies to pathogen discovery are discussed.

160 citations


Journal ArticleDOI
TL;DR: To be effective and durable, sustainable disease management requires a significant shift in emphasis to overtly include ecoevolutionary principles in the design of adaptive management programs aimed at minimizing the evolutionary potential of plant pathogens.
Abstract: Wild plants and their associated pathogens are involved in ongoing interactions over millennia that have been modified by coevolutionary processes to limit the spatial extent and temporal duration of disease epidemics. These interactions are disrupted by modern agricultural practices and social activities, such as intensified monoculture using superior varieties and international trading of agricultural commodities. These activities, when supplemented with high resource inputs and the broad application of agrochemicals, create conditions uniquely conducive to widespread plant disease epidemics and rapid pathogen evolution. To be effective and durable, sustainable disease management requires a significant shift in emphasis to overtly include ecoevolutionary principles in the design of adaptive management programs aimed at minimizing the evolutionary potential of plant pathogens by reducing their genetic variation, stabilizing their evolutionary dynamics, and preventing dissemination of pathogen variants carrying new infectivity or resistance to agrochemicals.

Journal ArticleDOI
TL;DR: Implementing the one fungus-one name system and linking names to validated type specimens, cultures, and reference sequences will provide the foundation on which the future of plant pathology and the communication of names of plant pathogens will rest.
Abstract: Scientific names are crucial in communicating knowledge about fungi. In plant pathology, they link information regarding the biology, host range, distribution, and potential risk. Our understanding of fungal biodiversity and fungal systematics has undergone an exponential leap, incorporating genomics, web-based systems, and DNA data for rapid identification to link species to metadata. The impact of our ability to recognize hitherto unknown organisms on plant pathology and trade is enormous and continues to grow. Major challenges for phytomycology are intertwined with the Genera of Fungi project, which adds DNA barcodes to known biodiversity and corrects the application of old, established names via epi- or neotypification. Implementing the one fungus–one name system and linking names to validated type specimens, cultures, and reference sequences will provide the foundation on which the future of plant pathology and the communication of names of plant pathogens will rest.

Journal ArticleDOI
TL;DR: The current view on chitin and LCO perception in innate immunity and endosymbiosis is described and how LCOs might modulate the immune system is questioned.
Abstract: Symbiotic nitrogen-fixing rhizobium bacteria and arbuscular mycorrhizal fungi use lipochitooligosaccharide (LCO) signals to communicate with potential host plants. Upon a compatible match, an intimate relation is established during which the microsymbiont is allowed to enter root (-derived) cells. Plants perceive microbial LCO molecules by specific LysM-domain-containing receptor-like kinases. These do not only activate a common symbiosis signaling pathway that is shared in both symbioses but also modulate innate immune responses. Recent studies revealed that symbiotic LCO receptors are closely related to chitin innate immune receptors, and some of these receptors even function in symbiosis as well as immunity. This raises questions about how plants manage to translate structurally very similar microbial signals into different outputs. Here, we describe the current view on chitin and LCO perception in innate immunity and endosymbiosis and question how LCOs might modulate the immune system. Furthermore, we discuss what it takes to become an endosymbiont.

Journal ArticleDOI
TL;DR: The emergence of unmanned aircraft systems (UASs, or drones) to sample plant pathogens in the lower atmosphere, coupled with source localization efforts, could aid in mitigating the spread of high-risk plant pathogens.
Abstract: Many high-risk plant pathogens are transported over long distances (hundreds of meters to thousands of kilometers) in the atmosphere. The ability to track the movement of these pathogens in the atmosphere is essential for forecasting disease spread and establishing effective quarantine measures. Here, we discuss the scales of atmospheric dispersal of plant pathogens along a transport continuum (pathogen scale, farm scale, regional scale, and continental scale). Growers can use risk information at each of these dispersal scales to assist in making plant disease management decisions, such as the timely application of appropriate pesticides. Regional- and continental-scale atmospheric features known as Lagrangian coherent structures (LCSs) may shuffle plant pathogens along highways in the sky. A promising new method relying on overlapping turbulent back-trajectories of pathogen-laden parcels of air may assist in localizing potential inoculum sources, informing local and/or regional management efforts such as...

Journal ArticleDOI
TL;DR: Functional analyses of a diverse group of genes encoding virulence factors indicate that successful host xylem colonization relies on specific Verticillium responses to various stresses, including nutrient deficiency and host defense-derived oxidative stress.
Abstract: The availability of genomic sequences of several Verticillium species triggered an explosion of genome-scale investigations of mechanisms fundamental to the Verticillium life cycle and disease process. Comparative genomics studies have revealed evolutionary mechanisms, such as hybridization and interchromosomal rearrangements, that have shaped these genomes. Functional analyses of a diverse group of genes encoding virulence factors indicate that successful host xylem colonization relies on specific Verticillium responses to various stresses, including nutrient deficiency and host defense-derived oxidative stress. Regulatory pathways that control responses to changes in nutrient availability also appear to positively control resting structure development. Conversely, resting structure development seems to be repressed by pathways, such as those involving effector secretion, which promote responses to host defenses. The genomics-enabled functional characterization of responses to the challenges presented by the xylem environment, accompanied by identification of novel virulence factors, has rapidly expanded our understanding of niche adaptation in Verticillium species.

Journal ArticleDOI
TL;DR: Although black leaf streak disease (BLSD), which is present throughout Asian, African, and American production areas, is a primary global concern, other diseases with limited distributions rival its impact.
Abstract: Banana (Musa spp.) is one of the world's most valuable primary agricultural commodities. Exported fruit are key commodities in several producing countries yet make up less than 15% of the total annual output of 145 million metric tons (MMT). Transnational exporters market fruit of the Cavendish cultivars, which are usually produced in large plantations with fixed infrastructures and high inputs of fertilizers, pesticides, and irrigation. In contrast, smallholders grow diverse cultivars, often for domestic markets, with minimal inputs. Diseases are serious constraints for export as well as smallholder production. Although black leaf streak disease (BLSD), which is present throughout Asian, African, and American production areas, is a primary global concern, other diseases with limited distributions, notably tropical race 4 of Fusarium wilt, rival its impact. Here, we summarize recent developments on the most significant of these problems.

Journal ArticleDOI
TL;DR: This review summarizes the current understanding of the transport processes that facilitate immunity and focuses on the dynamic localization of the FLS2 receptor and discusses the pathways that regulate receptor transport within the cell and their link to F LS2-mediated immunity.
Abstract: A significant challenge for plants is to induce localized defense responses at sites of pathogen attack. Therefore, host subcellular trafficking processes enable accumulation and exchange of defense compounds, which contributes to the plant on-site defenses in response to pathogen perception. This review summarizes our current understanding of the transport processes that facilitate immunity, the significance of which is highlighted by pathogens reprogramming membrane trafficking through host cell translocated effectors. Prominent immune-related cargos of plant trafficking pathways are the pattern recognition receptors (PRRs), which must be present at the plasma membrane to sense microbes in the apoplast. We focus on the dynamic localization of the FLS2 receptor and discuss the pathways that regulate receptor transport within the cell and their link to FLS2-mediated immunity. One emerging theme is that ligand-induced late endocytic trafficking is conserved across different PRR protein families as well as across different plant species.

Journal ArticleDOI
TL;DR: A systems biology approach using contemporary technologies in molecular biology, -omics, and cell biology aids in exploring the comparative molecular biology of GLRaVs and deciphering the complex network of host-virus-vector interactions to bridge the gap between genomics and phenomics of leafroll disease.
Abstract: Grapevine leafroll is the most complex and intriguing viral disease of grapevine (Vitis spp.). Several monopartite closteroviruses (family Closteroviridae) from grapevines have been molecularly characterized, yet their role in disease etiology is not completely resolved. Hence, these viruses are currently designated under the umbrella term of Grapevine leafroll-associated viruses (GLRaVs). This review examines our current understanding of the genetically divergent GLRaVs and highlights the emerging picture of several unique aspects of the leafroll disease pathosystem. A systems biology approach using contemporary technologies in molecular biology, -omics, and cell biology aids in exploring the comparative molecular biology of GLRaVs and deciphering the complex network of host-virus-vector interactions to bridge the gap between genomics and phenomics of leafroll disease. In addition, grapevine-infecting closteroviruses have a great potential as designer viruses to pursue functional genomics and for the rational design of novel disease intervention strategies in this agriculturally important perennial fruit crop.

Journal ArticleDOI
TL;DR: Leaf rust of barley is caused by the macrocyclic, heteroecious rust pathogen Puccinia hordei, with aecia reported from selected species of the genera Ornithogalum, Leopoldia, and Dipcadi, and uredinia and telia occurring on Hordeum vulgare ssp.
Abstract: Leaf rust of barley is caused by the macrocyclic, heteroecious rust pathogen Puccinia hordei, with aecia reported from selected species of the genera Ornithogalum, Leopoldia, and Dipcadi, and uredinia and telia occurring on Hordeum vulgare, H. vulgare ssp. spontaneum, Hordeum bulbosum, and Hordeum murinum, on which distinct parasitic specialization occurs. Although Puccinia hordei is sporadic in its occurrence, it is probably the most common and widely distributed rust disease of barley. Leaf rust has increased in importance in recent decades in temperate barley-growing regions, presumably because of more intensive agricultural practices. Although total crop loss does not occur, under epidemic conditions yield reductions of up to 62% have been reported in susceptible varieties. Leaf rust is primarily controlled by the use of resistant cultivars, and, to date, 21 seedling resistance genes and two adult plant resistance (APR) genes have been identified. Virulence has been detected for most seedling resistance genes but is unknown for the APR genes Rph20 and Rph23. Other potentially new sources of APR have been reported, and additivity has been described for some of these resistances. Approaches to achieving durable resistance to leaf rust in barley are discussed.

Journal ArticleDOI
TL;DR: This review highlights more general levers and promising approaches to optimize disease control in perennial plants from sharka epidemiology to gain insights from this worldwide experience.
Abstract: Many plant epidemics that cause major economic losses cannot be controlled with pesticides. Among them, sharka epidemics severely affect prunus trees worldwide. Its causal agent, Plum pox virus (PPV; genus Potyvirus), has been classified as a quarantine pathogen in numerous countries. As a result, various management strategies have been implemented in different regions of the world, depending on the epidemiological context and on the objective (i.e., eradication, suppression, containment, or resilience). These strategies have exploited virus-free planting material, varietal improvement, surveillance and removal of trees in orchards, and statistical models. Variations on these management options lead to contrasted outcomes, from successful eradication to widespread presence of PPV in orchards. Here, we present management strategies in the light of sharka epidemiology to gain insights from this worldwide experience. Although focused on sharka, this review highlights more general levers and promising approaches to optimize disease control in perennial plants.

Journal ArticleDOI
TL;DR: The purpose of this review is to provide a necessary background of systems and reagents developed for CTV that can be used for continued progress in this area and to point out the value of the CTV-citrus system in answering important questions on plant-virus interactions and developing new methods for controlling plant diseases.
Abstract: Virus diseases of perennial trees and vines have characteristics not amenable to study using small model annual plants. Unique disease symptoms such as graft incompatibilities and stem pitting cause considerable crop losses. Also, viruses in these long-living plants tend to accumulate complex populations of viruses and strains. Considerable progress has been made in understanding the biology and genetics of Citrus tristeza virus (CTV) and in developing it into a tool for crop protection and improvement. The diseases in tree and vine crops have commonalities for which CTV can be used to develop a baseline. The purpose of this review is to provide a necessary background of systems and reagents developed for CTV that can be used for continued progress in this area and to point out the value of the CTV-citrus system in answering important questions on plant-virus interactions and developing new methods for controlling plant diseases.

Journal ArticleDOI
TL;DR: The power of molecular tools in accurately identifying bacterial pathogenesis is of value to the farmer, diagnostician, phytobacteriologist, and taxonomist.
Abstract: Knowing the identity of bacterial plant pathogens is essential to strategic and sustainable disease management in agricultural systems. This knowledge is critical for growers, diagnosticians, extension agents, and others dealing with crops. However, such identifications are linked to bacterial taxonomy, a complicated and changing discipline that depends on methods and information that are often not used by those who are diagnosing field problems. Modern molecular tools for fingerprinting and sequencing allow for pathogen identification in the absence of distinguishing or conveniently tested phenotypic characteristics. These methods are also useful in studying the etiology and epidemiology of phytopathogenic bacteria from epidemics, as was done in numerous studies conducted in California's Salinas Valley. Multilocus and whole-genome sequence analyses are becoming the cornerstones of studies of microbial diversity and bacterial taxonomy. Whole-genome sequence analysis needs to become adequately accessible, ...

Journal ArticleDOI
TL;DR: Ribosomal DNA frameworks with sequence data from more than 2,700 nematode taxa combined with detailed morphological information allow for explicit hypotheses on the origin of agronomically important plant parasites, such as root-knot, cyst, and lesion nematodes.
Abstract: Within the species-rich and trophically diverse phylum Nematoda, at least four independent major lineages of plant parasites have evolved, and in at least one of these major lineages plant parasitism arose independently multiple times. Ribosomal DNA data, sequence information from nematode-produced, plant cell wall-modifying enzymes, and the morphology and origin of the style(t), a protrusible piercing device used to penetrate the plant cell wall, all suggest that facultative and obligate plant parasites originate from fungivorous ancestors. Data on the nature and diversification of plant cell wall-modifying enzymes point at multiple horizontal gene transfer events from soil bacteria to bacterivorous nematodes resulting in several distinct lineages of fungal or oomycete-feeding nematodes. Ribosomal DNA frameworks with sequence data from more than 2,700 nematode taxa combined with detailed morphological information allow for explicit hypotheses on the origin of agronomically important plant parasites, such as root-knot, cyst, and lesion nematodes.

Journal ArticleDOI
TL;DR: Uncertainty remains regarding the role of locally produced inoculum in disease outbreaks, but evidence suggests multiple sources of primary inoculum could be important and concepts and approaches developed in this pathosystem can guide future efforts when responding to incursions of new or reemerging downy mildew pathogens.
Abstract: The resurgence of cucurbit downy mildew has dramatically influenced production of cucurbits and disease management systems at multiple scales. Long-distance dispersal is a fundamental aspect of epidemic development that influences the timing and extent of outbreaks of cucurbit downy mildew. The dispersal potential of Pseudoperonospora cubensis appears to be limited primarily by sporangia production in source fields and availability of susceptible hosts and less by sporangia survival during transport. Uncertainty remains regarding the role of locally produced inoculum in disease outbreaks, but evidence suggests multiple sources of primary inoculum could be important. Understanding pathogen diversity and population differentiation is a critical aspect of disease management and an active research area. Underpinning advances in our understanding of pathogen biology and disease management has been the research capacity and coordination of stakeholders, scientists, and extension personnel. Concepts and approaches developed in this pathosystem can guide future efforts when responding to incursions of new or reemerging downy mildew pathogens.

Journal ArticleDOI
TL;DR: The study of plant disease epidemics at a landscape scale can be extended to allow for predictions about disease occurrence at this scale, and incorporation of all components of the disease triangle may be one way to improve these systems.
Abstract: The study of plant disease epidemics at a landscape scale can be extended to allow for predictions about disease occurrence at this scale. Examined within the context of the disease triangle, systems developed to incorporate information primarily about the pathogen and conditions conducive to the infection process. Parametric methods can be used to relate environmental conditions to disease, and specifically relate environment to the inoculum production, the resulting infection process, or both. Aspects relating to the presence or absence of the host plant within the landscape, or patterns of the host within the landscape, are much rarer in disease prediction, although analyses incorporating these factors have been conducted. Predictive systems at the landscape scale may concentrate only on the conditions for infection or possible migratory paths of pathogen propagules. Incorporation of all components of the disease triangle may be one way to improve these systems.

Journal ArticleDOI
TL;DR: Reconstruction of migration histories has confirmed previous hypotheses based on observational data and led to unexpected new findings on the origins of pathogens and source populations for past and recent migration.
Abstract: Trade in plant and plant products has profoundly affected the global distribution and diversity of plant pathogens. Identification of migration pathways can be used to monitor or manage pathogen movement for proactive disease management or quarantine measures. Genomics-based genetic marker discovery is allowing unprecedented collection of population genetic data for plant pathogens. These data can be used for detailed analysis of the ancestry of population samples and therefore for analysis of migration. Reconstruction of migration histories has confirmed previous hypotheses based on observational data and led to unexpected new findings on the origins of pathogens and source populations for past and recent migration. The choice of software for analysis depends on the type of migration being studied and the reproductive mode of the pathogen. Biased sampling and complex population structures are potential challenges to accurate inference of migration pathways.

Journal ArticleDOI
TL;DR: This chapter represents a travelog of my life and career and the philosophical points I acquired along the way, some of which are: the importance of positioning oneself; going for the big enchilada; music, the international language; the red zone of biotechnology; the human side of bi technology; the transgenic papaya story; and my leadership time at USDA in Hawaii.
Abstract: This chapter represents a travelog of my life and career and the philosophical points I acquired along the way. I was born on a sugar plantation on the island of Hawaii and early on had a stuttering problem. I attended the Kamehameha Schools and received my BS and MS degrees from the University of Hawaii and my Ph.D. from the University of California at Davis. I link my life and career to various principles and events, some of which are: the importance of positioning oneself; going for the big enchilada; music, the international language; the red zone of biotechnology; the human side of biotechnology; the transgenic papaya story; and my leadership time at USDA in Hawaii. The guiding light throughout my career were the words from Drs. Eduardo Trujillo and Robert Shepherd, respectively, “Dennis, don't just be a test tube scientist, do something to help people” and “Now tell me, what have you really accomplished?”