Fusarium
head blight (FHB) is a devastating disease of barley that leads to significant
losses for the malting and brewing industry; however, there has been
insufficient attention towards understanding the new fungal growth and the
production of deoxynivalenol mycotoxin during the malting process. Field trials
were carried out in 2019, 2020 and 2021 at Agriculture and Agri-Food Canada-Brandon
Research and Development Centre, Brandon, MB. Barley varieties of different FHB
resistant levels: Newdale (moderately resistant to moderately susceptible) and
AAC Goldman (moderately resistant) were inoculated with single strain conidial
suspensions of each of seven different Fusarium graminearum strains, plus
a non-inoculated control. The severity of FHB (as a percentage of visibly
symptomatic spikelets) was higher in Newdale than in AAC Goldman in all three
years of the study (9% vs. 3%, respectively in 2019; 38% vs. 21% in 2020; 3.5%
vs. 0.6% in 2021). FHB in non-inoculated controls was present at low levels compared
to inoculated treatments each year. Cultivar differences were also evident and
consistent across years when Fusarium density was assessed by
quantitative PCR (Fusarium: barley
gene abundance ratios averaged 74.3 in Newdale vs. 36.5 in AAC Goldman in 2019;
9.7 vs. 4.4 in 2020; 22.1 vs. 13.9 in 2021) and in non-inoculated controls, the
Fusarium density was at very low levels. Deoxynivalenol content
(determined via ELISA) in the harvested grain was also higher in Newdale than
in AAC Goldman (11.6 vs. 5.0 ppm in 2019; 1.2 vs 0.7 ppm in 2020). We
micro-malted this Fusarium-infested barley
and found that cultivar differences in susceptibility factors persisted through
malting; Fusarium density in finished malt remained higher in Newdale
than in AAC Goldman (17.0 vs. 12.4 in 2019; 4.3 vs. 2.1 in 2020; 19.0 vs. 18.2
in 2021), as did deoxynivalenol content in the finished malt (3.8 ppm in
Newdale vs. 1.4 ppm in AAC Goldman for 2019). Both Fusarium density and
deoxynivalenol content were significantly correlated between barley and
finished malt (P < 0.05). Differences among Fusarium strains were less frequent than expected, although in
general deoxynivalenol content was higher for pathogen strains with a 3-acetyl-deoxynivalenol
chemotype, compared to those with a 15-acetyl-deoxynivalenol chemotype. Future
study objectives will be to understand the relationship between Fusarium
trait variability and malt quality parameters which will suggest more effective
criteria for grading barley grain or predicting final quality at early stages
of malting.