ROLE OF CHEMOTYPE IN AGGRESSIVENESS, TOXICITY, AND COMPETITIVE-NESS OF FUSARIUM GRAMINEARUM ON WHEAT
Author ORCID Identifier
https://orcid.org/0009-0009-7190-6428
Date Available
8-20-2026
Year of Publication
2025
Document Type
Master's Thesis
Degree Name
Master of Science (MS)
College
Agriculture, Food and Environment
Department/School/Program
Plant Pathology
Faculty
Dr. Lisa Vaillancourt
Abstract
Fusarium Head Blight (FHB) of wheat, caused by the fungus Fusarium graminearum, is a devastating disease that led to epidemics in the U.S. during the 1990s, resulting in economic losses exceeding $2.6 billion. Typical symptoms include bleached spikelets and shriveled grains, often contaminated with trichothecene mycotoxins that make them unsafe for food or feed. FHB severity and mycotoxin production are influenced by a complex interplay between host genotype, environmental factors, and pathogen genotype. Integrated management practices that include the use of more resistant cultivars, crop rotation, and fungicide applications help to reduce disease incidence and severity. Disease forecasting models are used to predict when disease levels will be high enough to require fungicide treatment. However, current forecasting models, which incorporate weather and host cultivar data, achieve only ~70% accuracy. These models might be improved if we could include more information about the impact of pathogen genetic variation on disease outcomes. Unfortunately, we still know relatively little about this corner of the disease triangle. In North America (NA), F. graminearum sensu stricto, comprising at least three genetically distinct populations (NA1, NA2, and NA3), is responsible for most FHB. While NA1 remains dominant, NA2 has expanded its range and increased in frequency in recent years across parts of the U.S. and Canada. Most NA strains of F. graminearum produce deoxynivalenol (DON) as the primary mycotoxin. In addition to DON, the NA1 population also typically produces a smaller amount of the 15-acetyl version of DON (15ADON), while the NA2 population mostly produces the 3-acetyl version (3ADON). Previous studies have shown that NA2 field isolates with the 3ADON chemotype are more aggressive and produce more toxin than NA1 15ADON isolates. It has been hypothesized that 3ADON confers a competitive advantage which has facilitated the expansion of the NA2 population. If there is a real link to aggressiveness and mycotoxin levels, it could be useful to incorporate regional chemotype data into risk assessment models. However, because all previous studies have been done using field isolates, it is difficult to separate the role of chemotype from contributions of other genetic factors that distinguish these populations. To address this issue, I used a classical genetics approach to test the hypothesis that the 3ADON chemotype directly increases aggressiveness, toxicity, and competitiveness in wheat heads, regardless of genetic background. I measured these traits in greenhouse assays among a group of progeny from a cross of an NA2 3ADON isolate and an NA1 15ADON tester. If chemotype plays a primary role, I expected that 3ADON progeny would induce more disease symptoms and produce more mycotoxin than 15ADON progeny, or would outcompete 15ADON progeny in co-inoculation experiments, either with or without fungicides. The objectives of my study were to: (1) develop mapping populations segregating for chemotype, and investigate whether genetic markers segregated in expected Mendelian ratios; (2) determine whether individual progeny and progeny pools segregating for the 3ADON versus 15ADON chemotype differed in aggressiveness, mycotoxin production, and competitiveness on susceptible and moderately resistant wheat cultivars with or without fungicides; and (3) identify single nucleotide polymorphism (SNP) markers associated with aggressiveness among the segregating progeny. Mapping populations from crosses between a heterothallic 15ADON tester strain and homothallic wild type strains with the 3ADON, NIV or NX2 chemotypes were created and evaluated for expected segregation patterns of two unlinked markers. The 3ADON and NIV crosses segregated normally, while the NX2 cross showed skewed ratios (3:1 instead of the expected 1:1) for the chemotype marker. Sixty-seven progeny of the 3ADON x 15ADON cross, including representatives of each chemotype, were used for point inoculation assays on susceptible Wheaton and moderately resistant Alsen wheat. Infected wheat heads were harvested and sent for mycotoxin analysis. The NA2 3ADON parent was more aggressive and more toxic than the NA1 15ADON parent, but there were no statistical differences between 3ADON and 15ADON progeny in either trait on either wheat variety. Additional experiments performed with a selected group of progeny with high versus low aggressiveness relative to the mean (high-low progeny), and including more replications, confirmed that progeny phenotypes were stable and reproducible. There was no bias in favor of either chemotype in the high or low groups. For competition assays, seven pools were created each containing 10 randomly selected progeny (five 15ADON and five 3ADON). Pools were inoculated onto Wheaton heads with or without fungicide. Wheat heads inoculated with the pools generally had equivalent amounts of 3ADON and 15ADON: there was no evidence for bias in favor of 3ADON. Progeny recovered from one experiment that included fungicide were 3ADON or 15ADON in equal ratios, providing no compelling evidence for a competitive advantage of 3ADON versus 15ADON so far. The high-low progeny, along with the parent strains, were subjected to whole-genome sequencing and SNP analysis. Analysis of SNP segregation patterns revealed a region on Chromosome 2 closely associated with aggressiveness that would be interesting to follow up in the future. Overall, results suggested that the 3ADON chemotype was not a primary determinant of increased aggressiveness, toxicity, or competitiveness relative to 15ADON in F. graminearum. Thus, the findings do not support the idea that the emergence of the NA2 population is primarily due to the 3ADON chemotype. Other genes in the NA2 background are probably as important or more important than the 3ADON TRI genes. My thesis demonstrates the value of classical genetic analysis of mapping populations to study the inheritance of important traits, analyze segregation patterns, and facilitate marker-assisted studies and functional genomics. We could use these tools to identify better markers for population genetics and risk assessment in future.
Digital Object Identifier (DOI)
https://doi.org/10.13023/etd.2025.441
Funding Information
USWBSI ( US Wheat and Barley Scab Initiative )
Recommended Citation
Goyal, Simran, "ROLE OF CHEMOTYPE IN AGGRESSIVENESS, TOXICITY, AND COMPETITIVE-NESS OF FUSARIUM GRAMINEARUM ON WHEAT" (2025). Theses and Dissertations--Plant Pathology. 49.
https://uknowledge.uky.edu/plantpath_etds/49
Included in
Agricultural Science Commons, Genetics Commons, Genomics Commons, Molecular Genetics Commons, Plant Pathology Commons
