Regional and field-specific differences in Fusarium species and mycotoxins associated with blighted North Carolina wheat

Authors: Cowger, Christina; Ward, Todd; NILSSON, KATHRYN - North Carolina State University; ARELLANO, CONSUELO - North Carolina State University; McCormick, Susan; Busman, Mark

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2020
Publication Date: 3/19/2020
Citation: Cowger, C., Ward, T.J., Nilsson, K., Arellano, C., McCormick, S.P., Busman, M. 2020. Regional and field-specific differences in Fusarium species and mycotoxins associated with blighted North Carolina wheat. International Journal of Food Microbiology. https://doi.org/10.1016/j.ijfoodmicro.2020.108594.
DOI: https://doi.org/10.1016/j.ijfoodmicro.2020.108594

Interpretive Summary: Although Fusarium graminearum is the main fungal species causing Fusarium head blight (FHB) in small-grain cereals internationally, in most countries various other Fusarium species are also involved. In the U.S., FHB surveys have focused on F. graminearum and the toxins it produces, which are in the class called trichothecenes and include deoxynivalenol (DON), nivalenol (NIV), and related toxins. A large-scale survey was undertaken across the state of North Carolina in 2014 to explore the frequency and distribution of F. graminearum capable of producing NIV, which is not monitored by grain buyers. Symptomatic wheat spikes were sampled from 59 wheat fields in 24 counties in three agronomic zones typical of several states east of the Appalachian Mountains: Piedmont, Coastal Plain, and Tidewater. Altogether, 2,197 isolates were identified to species using DNA sequence-based methods. NIV- producing isolates were rare statewide (2.2%), and never more than 12% in a single field, indicating that routine testing for NIV is probably unnecessary. Surprisingly, however, although F. graminearum was the majority species detected, species in the Fusarium tricinctum species complex (FTSC) were frequent, and even dominant in some fields. These FTSC strains do not produce trichothecenes, and instead produce what are called “emerging mycotoxins.” The FTSC percentage was 50-100% in four fields, 30-49% in five fields, 20-29% in five fields, and <20% in the remaining 45 fields. FTSC species were significantly more frequent in the Coastal Plain than in the Piedmont or Tidewater (P < 0.05). Moniliformin concentrations in samples ranged from 0.0 to 38.7 parts per million. The patchy occurrence of the FTSC species in wheat crops showed the need to learn more about the possible presence of their mycotoxins and the factors that allow them to sometimes out-compete trichothecene producers. Sampling a large number of wheat fields within a given area led to the unexpected discovery of a minority FHB-causing population.

Technical Abstract: Worldwide, while Fusarium graminearum is the main causal species of Fusarium head blight (FHB) in small-grain cereals, a diversity of FHB-causing species belonging to different species complexes has been found in most countries. In the U.S., FHB surveys have focused on the Fusarium graminearum species complex (FGSC) and the frequencies of 3-ADON, 15-ADON, and nivalenol (NIV) chemotypes. A large-scale survey was undertaken across the state of North Carolina in 2014 to explore the frequency and distribution of F. graminearum capable of producing NIV, which is not monitored at grain intake points. Symptomatic wheat spikes were sampled from 59 wheat fields in 24 counties located in three agronomic zones typical of several states east of the Appalachian Mountains: Piedmont, Coastal Plain, and Tidewater. Altogether, 2,197 isolates were identified to species using DNA sequence-based methods. Surprisingly, although F. graminearum was the majority species detected, species in the Fusarium tricinctum species complex (FTSC) that produce “emerging mycotoxins” were frequent, and even dominant in some fields. The FTSC percentage was 50-100% in four fields, 30-49% in five fields, 20-29% in five fields, and <20% in the remaining 45 fields. FTSC species were at significantly higher frequency in the Coastal Plain than in the Piedmont or Tidewater (P < 0.05). Moniliformin concentrations in samples ranged from 0.0 to 38.7 µg g-1. NIV producing isolates were rare statewide (2.2%), and never more than 12% in a single field, indicating that routine testing for NIV is probably unnecessary. The patchy distribution of FTSC species in wheat crops demonstrated the need to investigate the potential importance of their mycotoxins and the factors that allow them to sometimes out-compete trichothecene producers. An increased sampling intensity of wheat fields led to the unexpected discovery of a minority FHB-causing population.