Quantitative Assessment of Fusarium graminearum Infection in Resistant and Susceptible Barley Genotypes Beyond Visual...

Fusarium head blight (FHB), primarily caused by Fusarium graminearum, damages cereal crops by inducing discoloration of spikes and producing deoxynivalenol (DON), which contaminates grains. A TaqMan multiplex real-time PCR previously demonstrated a strong correlation between DON and Fusarium biomass measured by Fusarium Tri5 over barley actin but a weaker association with severity. To investigate this observed disconnection, we analyzed data from 340 spikes of susceptible (Explorer) and resistant (AAC Synergy) barley at rating, sourced from a single field plot inoculated with F. graminearum and categorized according to severity rating categories (SRCs). F. graminearum load was measured externally via the Tri5 gene and internally through Fusarium biomass and colony-forming units (CFUs), in addition to DON levels, to identify reliable infection indicators. Significant genotype × SRC interactions were observed across all measurements, including Tri5 (P = 0.0003), biomass (P = 0.0031), CFUs (P = 0.0012), and DON (P = 0.0022). The genotype influenced Tri5 and CFUs but did not significantly affect biomass or DON levels. SRC had a notable impact on all four metrics, with higher visual severity correlating with increased Tri5 levels, Fusarium DNA ratios, and CFU counts, thereby indicating greater fungal presence and biomass. Although severity correlated strongly with these measurements, it did not account for differences in genotype response. The combination of real-time PCR and CFU assays offers potential for improving future screening for FHB resistance. These findings underscore the importance of employing diverse measurement approaches to accurately evaluate F. graminearum infection in barley spikes. [Formula: see text] Copyright © 2026 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.