Effect of Photoperiod on Growth and Production of Trichothecene Mycotoxins in Fusarium graminearum

Fusarium graminearum is a plant-pathogenic and mycotoxin-producing fungus of major concern to cereal production worldwide. There are genetically distinct populations of the pathogen that are associated with different trichothecene mycotoxin profiles. A recent study has identified key differences in genes associated with light response and circadian regulation among the major North American F. graminearum populations. It is currently unclear how these populations differ in their response to photoperiod (hours of light per day). Therefore, we evaluated the effects of photoperiod on growth and trichothecene production in isolates representing the three most prominent North American populations (NA1, NA2 and NA3) of F. graminearum. Photoperiod had a profound effect on fungal growth, colony morphology, and trichothecene production. This effect varied by substrate (i.e., fungal growth medium or plant host) and among pathogen populations. Photoperiod had a considerable impact on inoculated corn seedlings, and total trichothecene production was substantially greater (2–25×) in inoculated corn compared with wheat. Photoperiod had little effect on trichothecene production in inoculated wheat seedlings, except for NA3. Differences in trichothecene production were not due to differences in fungal biomass, but likely the result of photoperiod-dependent gene expression changes to trichothecene biosynthesis.