Welcome to IMC 2018 International Mycological Congress
Conference Calendar

 

Displaying One Session

Symposia
Location
202 B+C 2nd Floor
Date
07/21/2018
Time
02:00 PM - 04:00 PM
Symposia

Population biology of Fusarium circinatum in the summer rainfall area of South Africa

Session Number
S44
Location
202 B+C 2nd Floor, Puerto Rico Convention Center, San Juan, Puerto Rico
Date
07/21/2018
Time
02:00 PM - 04:00 PM
Presentation Number
S44-1
Authors
  • F. Fru
  • E. Steenkamp
  • M. Wingfield
  • J. Roux
  • L. De Vos

Abstract

Abstract

Pine pitch canker, caused by Fusarium circinatum, started appearing in the winter rainfall regions of South Africa in 2005. More recently, however, outbreaks of the disease have also been reported in summer rainfall regions, which include the more important plantation growing areas of KwaZulu-Natal and Limpopo in the eastern parts of South Africa. The last detailed analysis of the population biology of F. circinatum in this region was conducted more than 10 years ago when the focus was on the pathogen’s genetics in commercial seedling nurseries. Here, we investigated the population genetics of 296 isolates of F. circinatum from different sites including both nurseries and plantations in the summer rainfall region of South Africa. For this purpose, we utilized microsatellite markers and mating type assays. Sixty-eight genotypes of the pathogen were identified, of which one was found across most of the sites in both nurseries and plantations. Although we found individuals of both mating types at most of the sites, the results of linkage disequilibrium analyses suggested that the fungus reproduces mainly asexually in the summer rainfall region of South Africa. Our data also indicated that disease outbreaks in the region were caused by relatively small numbers of highly abundant genotypes. This study confirms the view that there were multiple introductions of F. circinatum in South Africa and that human activity likely play an important role in the distribution of the fungus. These findings have serious negative implications for future pine disease management strategies in the country.

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Symposia

A phylogenomic view of the Fusarium oxysporum Species Complex provides a robust framework for addressing questions in systematics, ecology and plant pathology

Session Number
S44
Location
202 B+C 2nd Floor, Puerto Rico Convention Center, San Juan, Puerto Rico
Date
07/21/2018
Time
02:00 PM - 04:00 PM
Presentation Number
S44-2
Authors
  • D. Geiser
  • B. Park
  • S. Kang
  • L. Lagoze
  • E. Wallace
  • M. Jiménez-Gasco
  • J. Demers
  • K. O'Donnell
  • A. Burkhardt
  • F. Martin
  • L. Fokkens
  • M. Rep

Abstract

Abstract

Members of the Fusarium oxysporum species complex (FOSC) cause devastating vascular wilt diseases on a broad array of crop plants. In addition, some FOSC are known to inhabit soils and plants as presumed non-pathogens, and others inhabit plumbing systems and are associated with serious human infections. Initial attempts to produce a comprehensive phylogeny of the FOSC were hindered by a lack of concordance between phylogenies inferred from different loci. With the goal of producing a highly resolved phylogeny, we used a phylogenomic approach to extract 41 highly informative orthologous protein-coding genes useful for inferring organismal history in this group. OrthoMCL was used to identify orthologous protein clusters from the genomes of the FOSC, F graminearum, F. verticillioides, and an undescribed species in the F. solani Species Complex (FSSC 11). From the initial set of 9037 orthologue clusters identified, 4056 were found to represent a single protein from each of the four Fusarium genomes. Of these 4056 putative single-copy orthologues, only one mapped to a “lineage-specific” chromosome previously identified in the FOSC, with three additional loci mapping to unassembled contigs. This is hypothesized to reflect a strong connection between gene orthology patterns and the core genome of the FOSC. The coding sequences of each putative orthologue were then extracted from ten additional FOSC genomes and subjected to neighbor-joining bootstrap analysis, as a simple means to assess phylogenetic signal. 41 loci that provided ≥70% bootstrap support at seven or more nodes in the phylogeny of the eleven FOSC were then extracted from complete genome sequences of >100 FOSC isolates. Resulting sequences, covering 69,201 nucleotide sites with 9479 parsimony-informative characters, were aligned and subjected to a phylogenetic analysis. The resulting tree showed highly supported terminal clades, providing evidence for species boundaries within the FOSC, along with signatures of historical recombination within terminal species lineages. In addition, relationships between pathogenic and non-pathogenic isolates within clades suggest possible models for acquisition and loss of pathogenicity determinants. This highly resolved view of the evolution of the FOSC based on its core genome provides a powerful vantage point for observing the evolutionary patterns associated with pathogenicity and niche adaptation in this extremely important group of fungi.

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Symposia

Characterization of the RNAi pathway required for ascospore formation in the cereal pathogen Fusarium graminearum

Session Number
S44
Location
202 B+C 2nd Floor, Puerto Rico Convention Center, San Juan, Puerto Rico
Date
07/21/2018
Time
02:00 PM - 04:00 PM
Presentation Number
S44-3
Authors
  • D. Kim
  • H. Kim
  • S. Yun

Abstract

Abstract

Fusarium graminearum, the causal agent of Fusarium head blight in cereal crops, produces sexual progeny (ascospore) as an important overwintering and dissemination strategy for completing the disease cycle. This homothallic ascomycetous species carries two opposite mating-type (MAT) loci in a single nucleus to control sexual development. Recently, we have identified a RNA interference (RNAi) pathway that controls a late stage of sexual development in F. graminearum. Using several molecular strategies, we have determined the functions of several genes involved in the putative RNAi pathway. In particular, we have focused on the role of FgSMS-2 encoding an Argonaute-like protein, which is a part of the RNA-induced silencing complex for specific cleavage of target mRNAs. Both gene deletion- and gene overexpression-strains of FgSMS-2 were defective in ascospore/asci maturation. A GFP-tagging analysis showed that FgSMS-2 was specifically localized on perinuclear regions inside the immature asci. A BiFC analysis revealed that FgSMS-2 was able to bind to a Dicer-like protein, FgDCL-1 in cytoplasmic region during the early stage of sexual development. In addition, we identified putative target gene sets of FgSMS-2 using transcriptomics and RNA-immunoprecipitation (RIP)-seq analyses. A total of 262 genes were up-regulated in the FgSMS-2 deletion strain under sexual development compared to its wild-type progenitor, and a total of 525 genes were identified from putative RNA samples co-precipitated with FgSMS-2. Using the same RNA samples used in RIP analysis, we were able to identify a total of 8,922 small RNAs (17~32 bp in size). Overall, it is likely that a RNAi pathway plays an important role during the sexual development in F. graminearum, particularly the Argonaute-like protein, FgSMS-2 protein, controls a set of mRNAs that might be unnecessary during meiotic event.

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Symposia

The structural and functional diversity of fungi in the sorghum-Striga interaction in Ethiopia

Session Number
S44
Location
202 B+C 2nd Floor, Puerto Rico Convention Center, San Juan, Puerto Rico
Date
07/21/2018
Time
02:00 PM - 04:00 PM
Presentation Number
S44-4
Authors
  • L. Lombard
  • M. Hernández-Restrepo
  • D. Etalo
  • J. Raaijmakers
  • P. Crous

Abstract

Abstract

Sorghum bicolor is a key staple crop for millions of people in sub-Saharan Africa, and grown primarily for household food security in drought-prone and resource-poor regions. Striga hermonthica is a parasitic weed of sorghum roots and other crops including maize. In Ethiopia, Striga infestation can cause severe yield loss annually. Current measures to control Striga include cultural and chemical methods as well as breeding for host resistance, of which none have proved to be singularly effective. Furthermore, several of these control measures are not accessible or too expensive for resource-poor famers. Hence, there is a strong need for novel, effective, affordable, integrated and durable control strategies. Key to developing these control strategies are a better understanding of the structure and functionality of the extant microbial diversity within the sorghum-Striga interaction, in which fungi play a major role. For sorghum and Striga, however, knowledge of the diversity, biogeography and metabolic potential of microbes is fragmentary or non-existent. Therefore, the goal of the PROMISE (promoting root microbes for integrated Striga eradication) research programme is to identify specific groups and functions of known & unknown microbes that, in conjunction with specific sorghum lines and agronomic practices, consistently suppress Striga infections, adversely affect the Striga seed bank and enhance sorghum productivity for smallholder farmers. To this end, fungal isolations were made from soils collected in different Ethiopian agroecologies displaying both Striga-suppressive and -conducive traits. Additionally, endo- and epiphytic fungal isolations were made from Striga seeds collected from six different sorghum growing regions in Ethiopia. To meet the goals of the PROMISE research programme, only fast-growing fungi, excluding members of the Eurotiales and Mucorales, were characterised using the ribosomal ITS fungal barcode in combination with LSU. Where required, secondary barcodes (cmdA, rpb2, tef1 and tub2) were used for species-level identification. The majority of the fungi identified from soils and Striga seeds belonged to the Hypocreales and Pleosporales. Additionally, several novel taxa were also identified. In conclusion, a high diversity of fungi was isolated from the different agroecological regions sampled in Ethiopia, some displaying their own unique diversity. This diversity in sorghum fields is mostly driven by soil structure and climatic conditions, which in turn could adversely affect the application of a fungus to disrupt the Striga life cycle.

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Symposia

Genetic linkage maps and genomes provide clues to growth rate differences in Fusarium

Session Number
S44
Location
202 B+C 2nd Floor, Puerto Rico Convention Center, San Juan, Puerto Rico
Date
07/21/2018
Time
02:00 PM - 04:00 PM
Presentation Number
S44-5
Authors
  • B. Wingfield
  • L. De Vos
  • S. Van Wyk
  • B. Swarlask-Parry
  • M. Wingfield
  • E. Steenkamp

Abstract

Abstract

Sequencing fungal genomes has become almost routine and this is also true in the case of Fusarium species. Close to a 100 genome sequences are now available for Fusarium spp. and in some cases numerous isolates of a species have been sequenced. Understanding the functions of the genes coded by these genome sequences, especially in non-model species, will be important in managing plant pathogens in the future. We have used a combination of genetic linkage maps for a hybrid cross between Fusarium circinatum and F. temperatum and whole genome sequences to identify genes involved in growth rate differences in these two species. Predicted quantitative trait loci (QTLs) for growth in culture were mapped onto the genome sequence of both parents. Two QTLs were investigated. One of these enabled the identification of a five gene indel specific to F. circinatum that was not present in any other Fusarium for which genome data are available. The other QTL involves an indel in which two genes are absent in some F. circinatum isolates. Further investigations of these QTLs will enable a better understanding of growth and potentially, also pathogenicity in F. circinatum and F. temperatum.
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