Performing Department
(N/A)
Non Technical Summary
The fungus Fusarium graminearum causes important diseases of wheat, barley, rice, maize, and other cereal crops. Fusarium Head Blight (FHB) of wheat and other small grains, and Gibberella Ear Rot (GER) of maize, are the most common and damaging of these in the U.S. and worldwide.Even more concerning than direct yield loss from reduced grain weight is contamination of infected grains with mycotoxins, e.g. deoxynivalenol (DON), that are dangerous for human and animal health, and subject to regulation to ensure compliance with low tolerance limits.Both FHB and GER have a complex epidemiology that includes multiple alternate hosts and a very strong influence of the environment on disease outcomes and toxin accumulation. The pathogen population exhibits a high degree ofvariation among strains, further contributing to the unpredictability of disease and toxin levels from year to year.Since a series of major epidemics in the U.S. cost wheat growers around $3 billion during the 1990s, FHB has received increased research attention and this has resulted in the development of improved disease forecasting models, more efficacious fungicides and application technologies, and new sources of resistance in wheat and barley. In contrast, there are very few similar resources for GER, despite total losses in the U.S. that were 160 times greater than those due to FHB in 2020-2022. Furthermore, infested maize stubble left in the field after harvest is a primary source of spores that cause FHB, which continues to be one of the most damaging diseases of wheat and barley in the U.S. With the existence of a single pathogen population causing most GER and FHB in N. America, we need to focus much more attention on monitoring, modeling, and managing Fusarium graminearum on maize in order to reduce losses from both of these important diseases. The proposed research will address this critical need by developing new tools and resources to study, track, and model Fusarium strainscausing GER. Our long-term goal is to identify markers that could be used to detect and diagnosepathogen strains that pose a particularly high risk(e.g., that have high levels of aggressiveness on wheat, corn, or both;that have increased tolerance to environmental stress like heat or drought;or that are more resistant to fungicides) so that we can effectively monitorshifts in the fungal population in the field. Incorporation of this information with disease forecasting models will help us to better manage FHB and GER disease epidemics, by providing better surveillance and prediction tools for growers.
Animal Health Component
(N/A)
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
Fusarium Head Blight (FHB) on wheat and Gibberella Ear Rot (GER) on maize, both caused by the Fusarium graminearum species complex (FGSC), cost U.S. farmers more than $750M from 2020-2022. After devastating epidemics in the 1990s, improved management options were developed for FHB. However, few similar resources exist for GER, even though infested maize stubble is the primary FHB inoculum source, and the same pathogen population affects both hosts. Fungal strains vary in aggressiveness and fitness, but current FHB treatments do not account for pathogen diversity. We know little about the role of maize versus wheat in structuring pathogen populations. We aim to improve pathogen surveillance and disease prediction by studying the influence of host on fungal population selection. This addresses the program area priorities of "advancing knowledge of invasive or established plant pests...leading to innovative and biologically-based strategies to manage pests"; "questions of intra- and interspecies interactions relevant to pest management"; and "factors that contribute to invasiveness and movement and dispersal dynamics of pests". Objectives are: (1) Analyze genome sequences of a geographically diverse collection of FGSC isolates from maize and wheat to identify loci experiencing differential host selection. 2) Characterize and compare population shifts among a diverse collection of FGSC isolates in continuous maize vs. continuous wheat vs. crop rotations in the field in two locations, or after multiple generations on maize ears under two different temperature regimes 3) Use controlled crosses between maize and wheat isolates to characterize loci conditioning high levels of aggressiveness to each host.
Project Methods
1) Analyze genome sequences of a geographically diverse collection of Fusarium graminearumspecies complex (FGSC)isolates from maize and wheat to identify loci experiencing differential host selection on wheat vs corn. In this first objective we will compile a representative collection of Fusarium graminearummaize isolates from N. America and Brazil, and subject them to whole genome sequencing (WGS). Once we have inferred subpopulations, assigned isolates to them, and inferred admixed isolates with mixed ancestry, we will measure genetic differentiation among the subpopulations and test for evidence of selective sweeps within them and gene flow between them. We will compare with a collection of public and newly generated sequence assemblies of FGSC from wheat from the same regions to evaluate evidence of host-associated or other selection or substructure. Inclusion of Brazilian isolates will be especially informative because of the broader genetic base of the pathogens there, and the differences in cultivation practices (specifically, the routine use of double cropping including maize after wheat and maize after maize). It will also indicate the extent of intercontinental gene flow.2) Characterize and compare population shifts among a diverse collection ofFGSC isolates in continuous maize vs. continuous wheat vs. crop rotations in the field in two geographic locations, or after multiple generations on maize ears under two different temperature regimes.For this objective, we will be conducting artificial selection experiments with populations of FGSC inoculated on maize vs. wheat grown continuously versus in various rotations to impose different types of host selection. Inoculum prepared from mixtures of Fusarium strains will be subjected to multiple cycles of selection under each cropping regime, and population shifts will be tracked after recovery of strains and identification of surviving clones by SNP genotyping using the Monsterplex genotyping platform. The aim is to identify genotypes or alleles that exhibit signs of positive selection in one or more of the cropping regimes, and to discover whether maize and wheat impose similar selective forces.3) Use controlled crosses between maize and wheat isolates of Fusarium graminearum to characterize loci conditioning high levels of aggressiveness to each host in greenhouse assays. In this objective, we will use controlled crosses among FGSC strains and Monsterplex genotyping of progenyto identify genetic regions associated with high levels of toxigenicity and aggressiveness on maize, and to determine whether these same regions determine high levels of toxigenicity and aggressiveness on wheat. We will also evaluate whether there are fitness tradeoffs associated with high aggressiveness on maize by comparing various fitness characteristics among progeny with high vs. low aggressiveness.