https://www2.clarku.edu/faculty/dhibbett/Reprints%20PDFs/Taylor%20et%20al%202000%20FGB.pdf

Phylogenetic Species Recognition and Species Concepts in Fungi

Morphological, thermal and rheological properties of starches from different botanical sources

The magnitude of fungal diversity: the 1.5 million species estimate revisited

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/

Heading for disaster: Fusarium graminearum on cereal crops.

One of the greatest impediments to the study of Fusarium has been the incorrect and confused application of species names to toxigenic and pathogenic isolates, owing in large part to intrinsic limitations of morphological species recognition and its application. To address this problem, we have created FUSARIUM-ID v. 1.0, a publicly available database of partial translation elongation factor 1-alpha (TEF) DNA sequences, presently representing a selected sample of the diversity of the genus diversity, with excellent representation of Type-B trichothecene toxin producers, and the Gibberella fujikuroi, Fusarium oxysporum and F. solani species complexes. Users can generate sequences using primers that are conserved across the genus, and use the sequence as a query to BLAST the database, which can be accessed at http://fusarium.cbio.psu.edu, or in a phylogenetic analysis. Correct identification of a known species in these groups often can be performed using this gene region alone. This growing database will contain only vouchered sequences attached to publicly available cultures. In the future, FUSARIUM-ID will be expanded to include additional sequences, including multiple sequences from the same species, sequences from new and revised species, and information from additional genes.

FUSARIUM-ID v. 1.0: A DNA sequence database for identifying Fusarium

During the past decade, the plant disease called scab or Fusarium head blight of wheat and barley has reached epidemic proportions in North America and elsewhere in the world. Scab is an economically devastating plant disease, not only because it causes significant reduction in seed yields and quality, but also because infested seeds are often contaminated with trichothecene and estrogenic mycotoxins that pose a serious threat to animal health and food safety. To test whether the primary etiological agent of scab, the fungus Fusarium graminearum, is panmictic throughout its range, allelic genealogies were constructed from six single-copy nuclear genes from strains selected to represent the global genetic diversity of this pathogen. Excluding one hybrid strain, all six genealogies recovered the same seven biogeographically structured lineages, suggesting that they represent phylogenetically distinct species among which gene flow has been very limited during their evolutionary history. Parsimony analysis of the combined data set comprising 7,120 aligned nucleotide characters resolved most relationships among the seven lineages of the F. graminearum clade and related fusaria included in the study. Phylogenetic evidence is also presented for introgressive hybridization and intragenic recombination among lineages of the F. graminearum clade in nature.

https://www.pnas.org/content/pnas/97/14/7905.full.pdf

Gene genealogies reveal global phylogeographic structure and reproductive isolation among lineages of Fusarium graminearum, the fungus causing wheat scab

Potato starch with anomalous stable (constant with time) paste viscosity has been proposed as a natural replacement for cross-linked starch, but its behavior and the influencing factors are not well understood. Starch from 44 samples of potato tubers representing 34 genotypes was analyzed for phosphorus, mean granule diameter, amylose, calcium, magnesium, sodium, and potassium. Except for granule diameter, sodium, and potassium, each of those properties correlated significantly with one or more of five paste characteristics determined using the Brabender Visco-amylograph. Three samples had a stable viscosity in 1 yr of the study, but their behavior was not associated with unusual values of the other measured properties. The stable viscosity is probably a heritable trait influenced by cultural and climatic factors.

Potato Starch Paste Behavior as Related to Some Physical/Chemical Properties

A rapid and reliable method to determine deoxynivalenol (DON) in wheat, barley, and malt is described. Samples are extracted with acetonitrile-water (84 + 16). Extracts are eluted through a C18-alumina (1 + 3) column, evaporated to dryness, and derivatized with trimethylsilylimidazole-trimethylchlorosilane (100 + 1). DON is identified and quantitated by capillary gas chromatography with electron capture detection. This method can quantitate DON levels from 0.2 to 40 ppm. Multiple analyses of wheat spiked at 2 ppm and of naturally contaminated wheat, malt, and barley resulted in coefficients of variation of 5.1, 5.1, 6.0, and 9.8%, respectively. Recoveries of DON spikes at 3 levels were 94-100% for wheat, 100-105% for barley, and 100-105% for malt. Results for wheat sample analyzed with this procedure (1.9 +/- 0.1 ppm DON) compared well with results for the same sample analyzed by enzyme-linked immunosorbent assay (1.9 ppm DON) and by liquid chromatography (1.7 ppm DON).

Beth K. Tacke

Papers

Gene genealogies reveal global phylogeographic structure and reproductive isolation among lineages of Fusarium graminearum, the fungus causing wheat scab

Potato Starch Paste Behavior as Related to Some Physical/Chemical Properties

Determination of deoxynivalenol in wheat, barley, and malt by column cleanup and gas chromatography with electron capture detection.