Browsing by Subject "Deoxynivalenol"

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    Exploring Variation for Fusarium Head Blight Resistance and Deoxynivalenol Distribution in the Naked Barley Diversity Panel
    (2022-07) Hawkins, John
    Hull-less or naked barley (Hordeum vulgare L.) is a grain of growing importance in food, feed, and malting applications. Fusarium Head Blight (FHB), a disease caused by fungi in the genus Fusarium, causes significant damage to barley grain through accumulation of mycotoxins and undesirable fungal proteins and reduction of grain mass and malting quality. The most important Fusarium mycotoxin in North America is deoxynivalenol (DON). Naked barley accumulates significant amounts of DON in hull tissue, which is discarded at threshing, providing a mechanism for limiting FHB discounts due to mycotoxin contamination. For this research, genome wide association studies were performed using the Naked Barley Diversity Panel genotyped with an array of 50,000 single nucleotide polymorphisms (SNPs) and phenotyped for traits associated with DON distribution in the barley spike. Three notable quantitative trait loci (QTLs) for disease related traits were discovered. A QTL on the short arm of chromosome 3H, linked to a hydroxyproline rich glycoprotein gene was associated with reduced FHB severity. Another QTL on the long arm of 3H, linked to sdw1, was associated with shorter plants, greater FHB severity under grain spawn inoculation, and earlier heading. A third QTL on the short arm of 2H, linked to PPD-H1, was associated with taller plants, later heading, and a greater proportion of the total DON being localized in the hull. Overall, there appears to be potential for the improvement of FHB resistance and DON mitigation in naked barley.
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    Factors affecting Fusarium head blight development and trichothecene accumulation in fusarium-infected wheat heads.
    (2010-06) Gautam, Pravin
    Fusarium head blight (FHB), primarily caused by Fusarium graminearum Schwabe, is an economically important disease as it results in yield loss and quality losses of infected grain and the accumulation of mycotoxins produced by the invading fungus. Environmental factors, host genetics, and isolate aggressiveness impact FHB development and subsequently trichothecene production and accumulation. Though it is well established that moisture around anthesis promotes FHB development and trichothecene accumulation, the role of moisture, either in the form of rainfall or mist-irrigation during the period from anthesis to harvest has been largely overlooked. A three year field experiment was conducted in 2006, 2007 and 2008 to examine the influence of environmental factors, especially moisture, host resistance, and pathogen variation with respect to mycotoxin production capacity and pathogen aggressiveness, on infection, FHB development and mycotoxin production and accumulation in planta. In mature harvested grain FHB severity, visually scabby kernel (VSK) and mycotoxin concentration were significantly higher in Wheaton (FHB susceptible) than in the other two cultivars examined, Alsen and 2375. Although FHB severities were not significantly different in plots receiving different durations of mist-irrigation, VSK were significantly lower in the treatments receiving the least amount of mist-irrigation (14 DAI) than for treatments receiving mist-irrigation for longer periods, suggesting that extended periods of moisture promote disease development. DON concentration in harvested grain was, however, significantly lower in the treatment receiving the longest duration of mist-irrigation than those treatments receiving less water. In the whole head samples, which were collected 0, 7, 11, 14, 21, 28 and 41 days after inoculation, DON and other trichothecenes either declined with increased durations of mist-irrigation or remained low while water was being applied by the misting system. However, trichothecene accumulation was observed to increase after the cessation of mist-irrigation, with increases being most pronounced for the treatments with shorter mist-irrigation periods. The largest reduction in DON observed as a result of extended mist-irrigation periods was seen in the susceptible cultivar Wheaton. The influence of host resistance and pathogen variation on infection, FHB infection, disease development and mycotoxin accumulation in planta was examined in the series of greenhouse experiments utilizing point and spray inoculations. The levels of FHB severity and mycotoxins were higher in spray inoculated experiment than point inoculation in all cultivars examined. Wheaton (FHB susceptible) had the highest FHB severity and levels of mycotoxins. Alsen (moderately resistant to FHB) had significantly lower FHB severities, DON, 15-ADON, 3-ADON and NIV than either 2375 or Wheaton. Though there were no significant differences in initial infection among cultivars examined, Alsen had reduced spread of FHB symptoms from initial infection presumably due to type II resistance. DON production did not peak in all treatments, but where evident, the peak was earlier in 2375 (11 dai) than Alsen and Wheaton (21 or 14 dai). Multiple peaks and declines in DON levels were also evident. The performance of isolates was highly variable, though generally isolates Butte86Ada-11 and B63A were the most aggressive isolates and 49-3 and B45A were the least. The impact of free moisture, such as that from irrigation systems or rainfall, on mycotoxin accumulation was evaluated in greenhouse experiments. Despite the similar levels of FHB severity observed, the levels of mycotoxins were significantly less in the plants that received a single six hour wetting treatment compared to the respective control. The loss of DON and other mycotoxins was evident in all cultivars examined. Further, DON and 15-ADON were detected in run-off water. The results of these studies suggest that the availability of free moisture such as from mist-irrigation or rainfall may increase FHB severity and VSK, although DON and other trichothecene concentrations may be concomitantly reduced. Leaching appears to contribute to reductions in DON following wetting events.
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    Trichothecene transport in the phytopathogen Fusarium graminearum and trichothecene production in the entomopathogen Beauveria bassiana.
    (2020-09) O'Mara, Sean
    This dissertation explores the transport mechanisms involved in the export of the trichothecene mycotoxin deoxynivalenol (DON) in the plant pathogenic fungus Fusarium graminearum, and the potential expression of a trichothecene biosynthetic gene homolog in the insect pathogen Beauveria bassiana. First, our current understanding of the biosynthesis and transport of fungal secondary metabolites is reviewed. The major classes of fungal secondary metabolites and the biosynthetic enzymes and gene clusters which produce them are covered, and notable examples of each secondary metabolite class are highlighted. This review emphasizes how our understanding of the biosynthesis of many secondary metabolites is far more complete than our understanding of the mechanisms which export or sequester the final bioactive molecule. Then, the role of the F. graminearum vesicular t-SNARE Sso2 in the export of DON is investigated. A knockout mutant of Sso2 is generated and shown to have an essential role in DON accumulation, virulence, and xenobiotic resistance. A double mutant, generated by crossing the Δsso2 mutant with the membrane-bound transporter mutant Δabc1, was shown to be further reduced in DON accumulation and virulence, indicating potentially interconnected, but independent, modes of DON export. Deletion of Sso2 is shown to down-regulate the expression of a number of F. graminearum secondary metabolite gene clusters and up-regulate many cellular repair gene categories. Subsequently, the role of Abc1 and other membrane-bound transporters in DON accumulation, virulence, and xenobiotic defense is investigated in further detail. Through in vitro, in planta, and heterologous expression studies it is shown that Abc1 plays the most substantial role in these processes, and other membrane-bound transporters may function primarily in defense and as accessory DON exporters. Afterwards, this dissertation examines the whether other Hypocreales fungi contain homologs for the trichothecene biosynthetic enzymes and identifies a putative trichothecene biosynthetic cluster in B. bassiana. Deletion attempts of the B. bassiana Tri5 homolog are undertaken but are unsuccessful, and further work suggests that a new antibiotic selection agent may be necessary. Expression studies indicate, however, that the BbTri5 homolog is not expressed in conditions known to induce trichothecene production in F. graminearum, bringing into question whether the B. bassiana trichothecene cluster is expressed in unknown conditions or not at all. This dissertation concludes by revisiting the major findings of each chapter and proposing future perspectives and experiments which have arisen throughout this body of research. Further examination of unused F. graminearum deletion mutants and heterologous expression of B. bassiana Tri homologs are emphasized for future consideration.
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    Using near isogenic barley lines to validate Deoxynivalenol (DON) QTL previously identified through association analysis
    (2013-01) Navara, Stephanie Lynn
    Fusarium head blight (FHB) is a serious disease of cereal grains caused by the fungal pathogen Fusarium graminearum. Deoxynivalenol (or DON), the associated trichothecene mycotoxin is of special concern to barley producers and consumers. A recent association mapping (AM) study of U.S. six-row spring barley identified several modest effect quantitative trait loci (QTL) for DON and FHB. To date, few studies have attempted to verify the results of association analyses, particularly for complex traits such as FHB and DON resistance in barley. Despite control measures used to mitigate the effects of population structure and multiple testing in AM, false positives may still occur. To verify previously reported associations we evaluated the effects of nine DON QTL using near isogenic lines (NILs) for each QTL region. Families of contrasting homozygous haplotypes for each region were derived from lines in the original AM populations that were heterozygous for DON QTL. Seventeen NIL families were evaluated for FHB and DON in three field experiments. Significant differences between contrasting NIL haplotypes were detected for three QTL across environments and/or genetic backgrounds, thereby confirming QTL from the original AM study. Several explanations for those QTL that were not confirmed are discussed, including the effect of genetic background and incomplete sampling of relevant haplotypes.