The aim of this review was to survey all fungal pathologists with an association with the journal Molecular Plant Pathology and ask them to nominate which fungal pathogens they would place in a 'Top 10' based on scientific/economic importance. The survey generated 495 votes from the international community, and resulted in the generation of a Top 10 fungal plant pathogen list for Molecular Plant Pathology. The Top 10 list includes, in rank order, (1) Magnaporthe oryzae; (2) Botrytis cinerea; (3) Puccinia spp.; (4) Fusarium graminearum; (5) Fusarium oxysporum; (6) Blumeria graminis; (7) Mycosphaerella graminicola; (8) Colletotrichum spp.; (9) Ustilago maydis; (10) Melampsora lini, with honourable mentions for fungi just missing out on the Top 10, including Phakopsora pachyrhizi and Rhizoctonia solani. This article presents a short resume of each fungus in the Top 10 list and its importance, with the intent of initiating discussion and debate amongst the plant mycology community, as well as laying down a bench-mark. It will be interesting to see in future years how perceptions change and what fungi will comprise any future Top 10.

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The Top 10 fungal pathogens in molecular plant pathology

INTRODUCTION. Internal Organization of the Plant Body. Summary of Types of Cells and Tissues. General References. DEVELOPMENT OF THE SEED PLANT. The Embryo. From embryo to the Adult Plant. Apical Meristems and Their Derivatives. Differentiation, Specialization, and Morphogenesis. References. THE CELL. Cytoplasm. Nucleus. Plastids. Mitochondria. Microbodies. Vacuoles. Paramural Bodies. Ribosomes. Dictyosomes. Endoplasmic Reticulum. Lipid Globules. Microtubules. Ergastic Substances. References. CELL WALL. Macromolecular Components and Their Organization in the Wall. Cell Wall Layers. Intercellular Spaces. Pits, Primary Pit--Fields, and Plasmodesmata. Origin of Cell Wall During Cell Division. Growth of Cell Wall. References. PARENCHYMA AND COLLENCHYMA. Parenchyma. Collenchyma. References. SCLERENCHYMA. Sclereids. Fibers. Development of Sclereids and Fibers. References. EPIDERMIS. Composition. Developmental Aspects. Cell Wall. Stomata. Trichomes. References. XYLEM: GENERAL STRUCTURE AND CELL TYPES. Gross Structure of Secondary Xylem. Cell Types in the Secondary Xylem. Primary Xylem. Differentiation of Tracheary Elements. References. XYLEM: VARIATION IN WOOD STRUCTURE. Conifer Wood. Dicotyledon Wood. Some Factors in Development of Secondary Xylem. Identification of Wood. References. VASCULAR CAMBIUM. Organization of Cambium. Developmental Changes in the Initial Layer. Patterns and Causal Relations in Cambial Activity. References. PHLOEM. Cell Types. Primary Phloem. Secondary Phloem. References. PERIDERM. Structure of Periderm and Related Tissues. Development of Periderm. Outer Aspect of Bark in Relation to Structure. Lenticels. References. SECRETORY STRUCTURES. External Secretory Structures. Internal Secretory Structures. References. THE ROOT: PRIMARY STATE OF GROWTH. Types of Roots. Primary Structure. Development. References. THE ROOT: SECONDARY STATE OF GROWTH AND ADVENTITIOUS ROOTS. Common Types of Secondary Growth. Variations in Secondary Growths. Physiologic Aspects of Secondary Growth in Roots. Adventitious Roots. References. THE STEM: PRIMARY STATE OF GROWTH. External Morphology. Primary Structure. Development. References. THE STEM: SECONDARY GROWTH AND STRUCTURAL TYPES. Secondary Growth. Types of Stems. References. THE LEAF: BASIC STRUCTURE AND DEVELOPMENT. Morphology. Histology of Angiosperm Leaf. Development. Abscission. References. THE LEAF: VARIATIONS IN STRUCTURE. Leaf Structure and Environment. Dicotyledon Leaves. Monocotyledon Leaves. Gymnosperm Leaves. References. THE FLOWER: STRUCTURE AND DEVELOPMENT. Concept. Structure. Development. References. THE FLOWER: REPRODUCTIVE CYCLE. Microsporogenesis. Pollen. Male Gametophyte. Megasporogenesis. Female Gametophyte. Fertilization. References. THE FRUIT. Concept and Classification. The Fruit Wall. Fruit Types. Fruit Growths. Fruit Abscission. References. THE SEED. Concept and Morphology. Seed Development. Seed Coat. Nutrient Storage Tissues. References. EMBRYO AND SEEDLING. Mature Embryo. Development of Embryo. Classification of Embryos. Seedling. References. Glossary. Index.

Anatomy of Seed Plants

Introduction: Botrytis cinerea (teleomorph: Botryotinia fuckeliana) is an airborne plant pathogen with a necrotrophic lifestyle attacking over 200 crop hosts worldwide. Although there are fungicides for its control, many classes of fungicides have failed due to its genetic plasticity. It has become an important model for molecular study of necrotrophic fungi. Taxonomy: Kingdom: Fungi, phylum: Ascomycota, subphylum: Pezizomycotina, class: Leotiomycetes, order: Helotiales, family: Sclerotiniaceae, genus: Botryotinia. Host range and symptoms: Over 200 mainly dicotyledonous plant species, including important protein, oil, fibre and horticultural crops, are affected in temperate and subtropical regions. It can cause soft rotting of all aerial plant parts, and rotting of vegetables, fruits and flowers post-harvest to produce prolific grey conidiophores and (macro)conidia typical of the disease. Pathogenicity: B. cinerea produces a range of cell-wall-degrading enzymes, toxins and other low-molecular-weight compounds such as oxalic acid. New evidence suggests that the pathogen triggers the host to induce programmed cell death as an attack strategy. Resistance: There are few examples of robust genetic host resistance, but recent work has identified quantitative trait loci in tomato that offer new approaches for stable polygenic resistance in future.

Botrytis cinerea: the cause of grey mould disease

Sclerotinia sclerotiorum and Botrytis cinerea are closely related necrotrophic plant pathogenic fungi notable for their wide host ranges and environmental persistence. These attributes have made these species models for understanding the complexity of necrotrophic, broad host-range pathogenicity. Despite their similarities, the two species differ in mating behaviour and the ability to produce asexual spores. We have sequenced the genomes of one strain of S. sclerotiorum and two strains of B. cinerea. The comparative analysis of these genomes relative to one another and to other sequenced fungal genomes is provided here. Their 38-39 Mb genomes include 11,860-14,270 predicted genes, which share 83% amino acid identity on average between the two species. We have mapped the S. sclerotiorum assembly to 16 chromosomes and found large-scale co-linearity with the B. cinerea genomes. Seven percent of the S. sclerotiorum genome comprises transposable elements compared to ,1% of B. cinerea. The arsenal of genes associated with necrotrophic processes is similar between the species, including genes involved in plant cell wall degradation and oxalic acid production. Analysis of secondary metabolism gene clusters revealed an expansion in number and diversity of B. cinerea-specific secondary metabolites relative to S. sclerotiorum. The potential diversity in secondary metabolism might be involved in adaptation to specific ecological niches. Comparative genome analysis revealed the basis of differing sexual mating compatibility systems between S. sclerotiorum and B. cinerea. The organization of the mating-type loci differs, and their structures provide evidence for the evolution of heterothallism from homothallism. These data shed light on the evolutionary and mechanistic bases of the genetically complex traits of necrotrophic pathogenicity and sexual mating. This resource should facilitate the functional studies designed to better understand what makes these fungi such successful and persistent pathogens of agronomic crops.

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Genomic Analysis of the Necrotrophic Fungal Pathogens Sclerotinia sclerotiorum and Botrytis cinerea

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The Top 10 fungal pathogens in molecular plant pathology: Top 10 fungal pathogens

Preface.- Acknowledgements.- Contributors.- 1: Botrytis spp. and diseases they cause in agricultural systems - an introduction Yigal Elad, Brian Williamson, Paul Tudzynski and Nafiz Delen.- 1 Introduction. 2. Geographical and ecological occurrence. 3. Variability and adaptability. 4. Quiescent, restricted and aggressive infection. 5. Molecular basis of host-parasite interactions. 6. References. 2: The Ecology of Botrytis on Plant Surfaces Gustav Holz, Sonja Coertze and Brian Williamson.- 1. Introduction. 2. Survival. 3. Inoculum production and dispersal. 4. Growth on plant surfaces. 5. Infection pathways on diverse plant organs. 6. Conclusion. 7. References. 3: Taxonomy and Genetic Variation of Botrytis and Botryotinia Ross E. Beever and Pauline L. Weeds.- 1. Introduction. 2. Taxonomy. 3. Botrytis cinerea. 4. Genetics of other species of Botrytis. 5. The future. 6. Acknowledgements. 7. References. 4: Approaches to Molecular Genetics and Genomics of Botrytis Paul Tudzynski and Verena Siewers.- 1. Introduction. 2. Generation of transgenic Botrytis strains. 3. Unbiased gene cloning systems. 4. Perspectives. 5. Acknowledgements. 6. References. 5: Morphology and Cellular Organisation in Botrytis Interactions with Plants Klaus B. Tenberge.- 1. Introduction. 2. Cytology and ultrastructure of Botrytis. 3. Imaging of infection. 4. Host response. 5. Conclusions. 6. Acknowledgements. 7. References. 6: Signalling in Botrytis cinerea Bettina Tudzynski and Christian Schulze Gronover.- 1. Introduction. 2. Ga subunits of hetrotrimeric G proteins. 3. cAMP signalling pathway. 4. MAP kinase pathways. 5. Genes of the Ras superfamily. 6. Calcineurin/cyclophilin A signalling. 7. Putative transmembrane receptor proteins. 8. Two-component signal transduction genes in Botrytis cinerea. 9. Further protein kinase encoding geneswith unknown function. 10. Conclusion. 11. References. 7: Extracellular Enzymes and Metabolites Involved in Pathogenesis of Botrytis Ilona Kars and Jan A.L. van Kan.- 1. Introduction. 2. Penetration of the host surface. 3. Killing of host cells. 4. Conversion of host tissue into fungal biomass. 5. Other enzymes potentially involved in pathogenesis. 6. Concluding remarks. 7. Acknowledgements. 8. References. 8: Botrytis cinerea Perturbs Redox Processes as an Attack Strategy in Plants Gary D. Lyon, Bernard A. Goodman and Brian Williamson.- 1. Introduction. 2. Hydrogen peroxide and other AOS. 3. Low molecular mass antioxidant molecules. 4. Perturbation of free radical chemistry as a result of Botrytis infection. 5. Production of oxalic acid. 6. Dynamics of iron redox chemistry. 7. Regulation of plant enzymes. 8. Botrytis-derived enzymes. 9. Generation of lipid peroxidation products. 10. Host signalling and programmed cell death. 11. Fungus-derived metabolites. 12. Conclusion. 13. Acknowledgements. 14. References. 9: Plant Defence Compounds against Botrytis Infection Peter van Baarlen, Laurent Legendre and Jan A.L. van Kan.- 1. Introduction. 2. Antimicrobial secondary metabolites. 3. Tolerance of Botrytis to antifungal metabolites. 4. Structural barriers and cell wall modifications. 5. Pathogenesis-related proteins. 6. Concluding remarks. 7. Acknowledgements. 8. References. 10: Phytohormones In Botrytis-Plant Interactions Amir Sharon, Yigal Elad, Radwan Barakat and Paul Tudzynski.- 1. Introduction. 2. Biosynthesis of plant hormones by B. cinerea. 3. Effect of plant hormones on B. cinerea and on disease development. 4. Conclusions. 5. Acknowledgement. 6. References. 11: Detection, Quantification and Immunolocalisation of Botrytis species Frances M. Dewey (Molly) and David Yohalem.- 1. Introduction. 2. Classical plating out method. 3. Immu

Botrytis: biology, pathology and control.

SUMMARY The oxidative burst, a transient and rapid accumulation of reactive oxygen species (ROS), is a widespread defence mechanism of higher plants against pathogen attack. There is increasing evidence that the necrotrophic fungal pathogen Botrytis cinerea itself generates ROS, and that this capability could contribute to the virulence of the fungus. Two potential H(2)O(2)-generating systems were studied with respect to their impact on the interaction of B. cinerea and its host plant Phaseolus vulgaris. A Cu-Zn-superoxide dismutase gene (bcsod1) and a putative glucose oxidase gene (bcgod1) were cloned and characterized, and deletion mutants were created using a gene-replacement methodology. Whereas the Deltabcgod1-mutants displayed normal virulence on bean leaves, the Deltabcsod1 mutants showed a significantly retarded development of lesions, indicating that the Cu-Zn SOD-activity is an important single virulence factor in this interaction system. Whether dismutation of (fungal or host) superoxide, or generation of H(2)O(2) (or both), are important for pathogenesis in this system remains to be elucidated.

Functional analysis of H2O2-generating systems in Botrytis cinerea: the major Cu-Zn-superoxide dismutase (BCSOD1) contributes to virulence on French bean, whereas a glucose oxidase (BCGOD1) is dispensable

Some leading characteristics and historical notes on Botrytis spp. are described here. Botrytis spp. infect many host plants in all climate areas of the world, infecting mainly upper plant parts at pre- and post-harvest stages. Bulbs, seeds and other propagation material also suffer infection. Infection can occur in high humidity in the presence or absence of water films. Infection may be quiescent, aggressive, restricted or widely developing. The production of high numbers of conidia poses a long lasting threat to susceptible hosts. Genotypic and phenotypic variation is most important in the broad spectrum pathogen B. cinerea. Moreover, changes in populations in response to selection by exposure to xenobiotics, especially fungicides, are quite common in the genus and fungicide resistance has been recorded in Botrytis populations throughout the history of the modern fungicide era. Detailed studies on the precise conditions that promote infection, disease development and survival of inoculum have provided the essential epidemiological information required for design of control strategies. For example, cultural methods have been developed that increase aeration and drying of the plant canopy to reduce the risk of Botrytis epidemics. The increasing requirement for alternative approaches to reduce farmers' dependency on use of fungicides led to the evaluation and exploitation of potential biocontrol agents capable of substantial disease suppression in a commercial context, and within integrated crop management systems.

Botrytis spp. and diseases they cause in agricultural systems - an introduction

Summary There is evidence that the necrotrophic fungal pathogen Botrytis cinerea is exposed to oxidative processes within plant tissues. The pathogen itself also generates active oxygen species and H(2)O(2) as pathogenicity factors. Our aim was to study how the pathogen may defend itself against cellular damage caused by the accumulation of H(2)O(2) and the role of an extracellular catalase in its detoxification during the infection of tomato and bean plants by B. cinerea. Chloronaphthol staining followed by light microscopy showed that H(2)O(2) accumulates in the infection zone in tomato and bean leaves. An extracellular catalase gene (denominated Bccat2) was cloned from B. cinerea. Exposure of mycelium to H(2)O(2) in liquid culture resulted in increased Bccat2 mRNA levels in a concentration-dependent manner. Bccat2 mRNA was detected at early stages of tomato leaf infection, suggesting that B. cinerea experiences oxidative stress. Bccat2-deficient mutants were generated by transformation-mediated gene disruption. Mutants were more sensitive then the wild-type strain to H(2)O(2)in vitro, but they partly compensated for the absence of BcCAT2 by activating other protective mechanisms in the presence of H(2)O(2). Bccat2-deficient mutants did not display a consistent reduction of virulence on bean and tomato leaves. Cerium chloride staining of infected leaf tissue for ultrastructural studies showed that Bccat2-deficient mutants were exposed to H(2)O(2) comparably to the wild-type. The results suggest that B. cinerea is a robust pathogen adapted to growing in hostile oxidizing environments in host tissues.

B. Williamson

Papers

Botrytis cinerea: the cause of grey mould disease

Botrytis: biology, pathology and control.

Functional analysis of H2O2-generating systems in Botrytis cinerea: the major Cu-Zn-superoxide dismutase (BCSOD1) contributes to virulence on French bean, whereas a glucose oxidase (BCGOD1) is dispensable

Botrytis spp. and diseases they cause in agricultural systems - an introduction

Functional analysis of an extracellular catalase of Botrytis cinerea