Pathogen profile update: Fusarium oxysporum
TL;DR: More than 120 different formae speciales have been identified based on specificity to host species belonging to a wide range of plant families as mentioned in this paper, which can cause severe losses in many vegetables and flowers, field crops, such as cotton, and plantation crops such as banana, date palm and oil palm.
Abstract: Taxonomy: Kingdom Fungi; Phylum Ascomycota; Class Sordariomycetes; Order Hypocreales; Family Nectriaceae; genus Fusarium. Host range: Very broad at the species level. More than 120 different formae speciales have been identified based on specificity to host species belonging to a wide range of plant families. Disease symptoms: Initial symptoms of vascular wilt include vein clearing and leaf epinasty, followed by stunting, yellowing of the lower leaves, progressive wilting, defoliation and, finally, death of the plant. On fungal colonization, the vascular tissue turns brown, which is clearly visible in cross-sections of the stem. Some formae speciales are not primarily vascular pathogens, but cause foot and root rot or bulb rot. Economic importance: Can cause severe losses in many vegetables and flowers, field crops, such as cotton, and plantation crops, such as banana, date palm and oil palm. Control: Use of resistant varieties is the only practical measure for controlling the disease in the field. In glasshouses, soil sterilization can be performed. Useful websites: http://www.broad.mit.edu/annotation/genome/fusarium_group/MultiHome.html; http://www.fgsc.net/Fusarium/fushome.htm; http://www.phi-base.org/query.php
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North Carolina State University1, Wageningen University and Research Centre2, University of the Free State3, Rothamsted Research4, University of Córdoba (Spain)5, Imperial College London6, Texas A&M University7, Max Planck Society8, Commonwealth Scientific and Industrial Research Organisation9, University of Bristol10
TL;DR: A short resumé of each fungus in the Top 10 list and its importance is presented, with the intent of initiating discussion and debate amongst the plant mycology community, as well as laying down a bench-mark.
Abstract: 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.
2,807 citations
641 citations
Agricultural Research Service1, University of California, Davis2, Pennsylvania State University3, North Carolina State University4, University of Georgia5, Wageningen University and Research Centre6, Broad Institute7, Centre national de la recherche scientifique8, Seoul National University9, Spanish National Research Council10, University of Warwick11, University of Western Ontario12, Agriculture and Agri-Food Canada13, University of Massachusetts Amherst14
TL;DR: Insight is revealed into the genetic mechanisms of niche adaptation of fungal wilt pathogens, advances the understanding of the evolution and development of their pathogenesis, and sheds light on potential avenues for the development of novel disease management strategies to combat destructive wilt diseases.
Abstract: The vascular wilt fungi Verticillium dahliae and V. albo-atrum infect over 200 plant species, causing billions of dollars in annual crop losses. The characteristic wilt symptoms are a result of colonization and proliferation of the pathogens in the xylem vessels, which undergo fluctuations in osmolarity. To gain insights into the mechanisms that confer the organisms' pathogenicity and enable them to proliferate in the unique ecological niche of the plant vascular system, we sequenced the genomes of V. dahliae and V. albo-atrum and compared them to each other, and to the genome of Fusarium oxysporum, another fungal wilt pathogen. Our analyses identified a set of proteins that are shared among all three wilt pathogens, and present in few other fungal species. One of these is a homolog of a bacterial glucosyltransferase that synthesizes virulence-related osmoregulated periplasmic glucans in bacteria. Pathogenicity tests of the corresponding V. dahliae glucosyltransferase gene deletion mutants indicate that the gene is required for full virulence in the Australian tobacco species Nicotiana benthamiana. Compared to other fungi, the two sequenced Verticillium genomes encode more pectin-degrading enzymes and other carbohydrate-active enzymes, suggesting an extraordinary capacity to degrade plant pectin barricades. The high level of synteny between the two Verticillium assemblies highlighted four flexible genomic islands in V. dahliae that are enriched for transposable elements, and contain duplicated genes and genes that are important in signaling/transcriptional regulation and iron/lipid metabolism. Coupled with an enhanced capacity to degrade plant materials, these genomic islands may contribute to the expanded genetic diversity and virulence of V. dahliae, the primary causal agent of Verticillium wilts. Significantly, our study reveals insights into the genetic mechanisms of niche adaptation of fungal wilt pathogens, advances our understanding of the evolution and development of their pathogenesis, and sheds light on potential avenues for the development of novel disease management strategies to combat destructive wilt diseases.
435 citations
TL;DR: This review discusses the current knowledge on interactions of vascular wilt pathogens with their host plants, with emphasis on host defense responses against this group of pathogens.
Abstract: Vascular wilts are among the most destructive plant diseases that occur in annual crops as well as in woody perennials. These diseases are generally caused by soil-borne bacteria, fungi, and oomycetes that infect through the roots and enter the water-conducting xylem vessels where they proliferate and obstruct the transportation of water and minerals. As a consequence, leaves wilt and die, which may lead to impairment of the whole plant and eventually to death of the plant. Cultural, chemical, and biological measures to control this group of plant pathogens are generally ineffective, and the most effective control strategy is the use of genetic resistance. Owing to the fact that vascular wilt pathogens live deep in the interior of their host plants, studies into the biology of vascular pathogens are complicated. However, to design novel strategies to combat vascular wilt diseases, understanding the (molecular) biology of vascular pathogens and the molecular mechanisms underlying plant defense against these pathogens is crucial. In this review, we discuss the current knowledge on interactions of vascular wilt pathogens with their host plants, with emphasis on host defense responses against this group of pathogens.
397 citations
TL;DR: An overview of the Panama disease and its causal agent, Fusarium oxysporum f. cubense, is presented in this paper, with an emphasis on tropical race 4 (TR4), a 'Cavendish'-killing variant of the pathogen that has spread dramatically in the Eastern Hemisphere.
Abstract: Banana (Musa spp.) is one of the world's most important fruits. In 2011, 145 million metric tons, worth an estimated $44 billion, were produced in over 130 countries. Fusarium wilt (also known as Panama disease) is one of the most destructive diseases of this crop. It devastated the 'Gros Michel'-based export trades before the mid-1900s, and threatens the Cavendish cultivars that were used to replace it; in total, the latter cultivars are now responsible for approximately 45% of all production. An overview of the disease and its causal agent, Fusarium oxysporum f. sp. cubense, is presented below. Despite a substantial positive literature on biological, chemical, or cultural measures, management is largely restricted to excluding F. oxysporum f. sp. cubense from noninfested areas and using resistant cultivars where the pathogen has established. Resistance to Fusarium wilt is poor in several breeding targets, including important dessert and cooking cultivars. Better resistance to this and other diseases is needed. The history and impact of Fusarium wilt is summarized with an emphasis on tropical race 4 (TR4), a 'Cavendish'-killing variant of the pathogen that has spread dramatically in the Eastern Hemisphere.
362 citations
References
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TL;DR: The gene-for-gene hypothesis suggests that for each gene that conditions reaction in the host there is a correspond ing gene in the parasite that conditions pathogenicity.
Abstract: One of the most successful means of controlling plant diseases has been the development of varieties with major or vertical resistance genes. This type of resistance is easily manipulated in a breeding program and is efIec tive until strains of the pathogen to which it does not confer resistance be come established. Then, if another gene that conditions resistance to the new strains of the pathogen is available, this resistance gene may be incorporated into the variety by the plant breeder. In doing this, the breeder either con sciously or unconsciously is applying the principle of the gene-far-gene hypothesis. Plants resistant to races that are virulent on old varieties possess the new resistance gene. With the diseases of some crops, this process has becn repeated at relatively frequent intervals (4D, 42, 82). However, in some instances a single gene has conferred adequate resistance for many years 80,82). In plant diseases caused by living organisms, the same phenomena: in fection type in rusts, percent of infected plants in smuts of cereals, fleck or lesion in apple scab, are criteria of both the reaction of the host and the pathogenicity of the parasite. They indicate the relative resistance or sus ceptibility of the host and the relative avirulence or virulence of the para site. The gene-for-gene hypothesis was proposed (20,25) as the simplest ex planation of the results of studies on the inheritance of pathogenicity in the .flax rust fungus, M elampsora lini. On varieties of flax, Linum usitatissimum that have one gene for resistance to the avirulent parent race, F 2 cultures of the fungus segregate into monofactorial ratios. On varieties having 2, 3, or 4 genes for resistance to the avirulent parent race, the F2 cultures segregate into bi-, trio, or tetra factorial ratios (20-22) respectively. This suggests that for each gene that conditions reaction in the host there is a correspond ing gene in the parasite that conditions pathogenicity. Each gene in either member of a host-parasite system may be identified only by its counterpart in the other member of the system.
3,019 citations
TL;DR: The fact that laccases only require molecular oxygen for catalysis makes them suitable for biotechnological applications for the transformation or immobilization of xenobiotic compounds.
Abstract: Laccases of fungi attract considerable attention due to their possible involvement in the transformation of a wide variety of phenolic compounds including the polymeric lignin and humic substances. So far, more than a 100 enzymes have been purified from fungal cultures and characterized in terms of their biochemical and catalytic properties. Most ligninolytic fungal species produce constitutively at least one laccase isoenzyme and laccases are also dominant among ligninolytic enzymes in the soil environment. The fact that they only require molecular oxygen for catalysis makes them suitable for biotechnological applications for the transformation or immobilization of xenobiotic compounds.
1,925 citations
TL;DR: Testing whether lineages of the Panama disease pathogen have a monophyletic origin by comparing DNA sequences of nuclear and mitochondrial genes indicates Panama disease of banana is caused by fungi with independent evolutionary origins.
Abstract: Panama disease of banana, caused by the fungus Fusarium oxysporum f. sp. cubense, is a serious constraint both to the commercial production of banana and cultivation for subsistence agriculture. Previous work has indicated that F. oxysporum f. sp. cubense consists of several clonal lineages that may be genetically distant. In this study we tested whether lineages of the Panama disease pathogen have a monophyletic origin by comparing DNA sequences of nuclear and mitochondrial genes. DNA sequences were obtained for translation elongation factor 1α and the mitochondrial small subunit ribosomal RNA genes for F. oxysporum strains from banana, pathogenic strains from other hosts and putatively nonpathogenic isolates of F. oxysporum. Cladograms for the two genes were highly concordant and a partition-homogeneity test indicated the two datasets could be combined. The tree inferred from the combined dataset resolved five lineages corresponding to “F. oxysporum f. sp. cubense” with a large dichotomy between two taxa represented by strains most commonly isolated from bananas with Panama disease. The results also demonstrate that the latter two taxa have significantly different chromosome numbers. F. oxysporum isolates collected as nonpathogenic or pathogenic to other hosts that have very similar or identical elongation factor 1α and mitochondrial small subunit genotypes as banana pathogens were shown to cause little or no disease on banana. Taken together, these results indicate Panama disease of banana is caused by fungi with independent evolutionary origins.
1,639 citations
TL;DR: Current knowledge on the pathogenicity, population genetics, evolution and genomics of Fusarium graminearum is summarized.
Abstract: SUMMARY
The rapid global re-emergence of Fusarium head blight disease of wheat and barley in the last decade along with contamination of grains with mycotoxins attributable to the disease have spurred basic research on the fungal causal agent. As a result, Fusarium graminearum quickly has become one of the most intensively studied fungal plant pathogens. This review briefly summarizes current knowledge on the pathogenicity, population genetics, evolution and genomics of Fusarium graminearum.
Taxonomy: Based on the sexual state Gibberella zeae (Schwein.) Petch: Superkingdom Eukaryota; Kingdom Fungi; Phylum Ascomycota; Subphylum Pezizomycotina; Class Sordariomycetidae; Subclass Hypocreomycetidae; Order Hypocreales; Family Nectriaceae; Genus Gibberella.
Host range: The pathogen is capable of causing head blight or ‘scab’ on wheat (Triticum), barley (Hordeum), rice (Oryza), oats (Avena) and Gibberella stalk and ear rot disease on maize (Zea). The fungus also may infect other plant species without causing disease symptoms. Other host genera cited for Gibberella zeae or F. graminearum sensu lato (see below) are Agropyron, Agrostis, Bromus, Calamagrostis, Cenchrus, Cortaderia, Cucumis, Echinochloa, Glycine, Hierochloe, Lolium, Lycopersicon, Medicago, Phleum, Poa, Schizachyrium, Secale, Setaria, Sorghum, Spartina and Trifolium.
Disease symptoms and signs: For wheat, brown, dark purple to black necrotic lesions form on the exterior surface of the florets and glume (Fig. 1). Although these lesion symptoms sometimes are referred to as scab, they are not formally related to the hyperplasia and hypertrophic epidermal growth associated with other scab diseases such as apple scab. Peduncles immediately below the inflorescence may become discoloured brown/purple. With time, tissue of the inflorescence often becomes blighted, appearing bleached and tan, while the grain within atrophies. Awns often become deformed, twisted and curved downward. In barley, infections are not always readily apparent in the field. Infected spikelets may show a browning or water-soaked appearance. Infected barley kernels show a tan to dark brown discolouration that can be similar to that caused by other kernel blighting organisms. During prolonged wet periods, pink to salmon-orange spore masses of the fungus are often seen on infected spikelets, glumes and kernels in both wheat and barley. For maize ear rot, infection occurs by way of colonizing silk and thus symptoms first appear at the ear apex. White mycelium, turning pink to red with time, colonizes kernels and may progress basipetally, covering the entire ear.
Figure 1.
Field-grown wheat inflorescence showing symptoms of Fusarium head blight. The third spikelet from the bottom shows a darkened necrotic lesion (‘scab’) whereas the second and fifth spikelets demonstrate tissue bleaching (‘blight’) symptoms. Photograph courtesy of Jacki Morrison, USDA ARS Cereal Disease Laboratory.
Useful websites: http://www.broad.mit.edu/annotation/fungi/fusarium/mips.gsf.de/genre/proj/fusarium/
http://www.cdl.umn.edu/scab/gz-consort.html
http://www.scabusa.org/
1,097 citations
TL;DR: The results indicate that the antagonistic interactions between multiple components of ABA and the JA-ethylene signaling pathways modulate defense and stress responsive gene expression in response to biotic and abiotic stresses.
Abstract: The plant hormones abscisic acid (ABA), jasmonic acid (JA), and ethylene are involved in diverse plant processes, including the regulation of gene expression during adaptive responses to abiotic and biotic stresses. Previously, ABA has been implicated in enhancing disease susceptibility in various plant species, but currently very little is known about the molecular mechanisms underlying this phenomenon. In this study, we obtained evidence that a complex interplay between ABA and JA-ethylene signaling pathways regulate plant defense gene expression and disease resistance. First, we showed that exogenous ABA suppressed both basal and JA-ethylene–activated transcription from defense genes. By contrast, ABA deficiency as conditioned by the mutations in the ABA1 and ABA2 genes, which encode enzymes involved in ABA biosynthesis, resulted in upregulation of basal and induced transcription from JA-ethylene responsive defense genes. Second, we found that disruption of AtMYC2 (allelic to JASMONATE INSENSITIVE1 [JIN1]), encoding a basic helix-loop-helix Leu zipper transcription factor, which is a positive regulator of ABA signaling, results in elevated levels of basal and activated transcription from JA-ethylene responsive defense genes. Furthermore, the jin1/myc2 and aba2-1 mutants showed increased resistance to the necrotrophic fungal pathogen Fusarium oxysporum. Finally, using ethylene and ABA signaling mutants, we showed that interaction between ABA and ethylene signaling is mutually antagonistic in vegetative tissues. Collectively, our results indicate that the antagonistic interactions between multiple components of ABA and the JA-ethylene signaling pathways modulate defense and stress responsive gene expression in response to biotic and abiotic stresses.
1,058 citations