Ten-Year Comparison of Fungicide Sensitivity and Mycotoxin Production of Fusarium Head Blight Isolates from Korea

Abstract

Fusarium head blight (FHB) is an important disease reducing yield and quality of wheat and barley. To study changes in fungicide efficacy over time, 161 FHB isolates (F. asiaticum and F. graminearum) were obtained from infected wheat and barley in the Jeolla provinces of the Republic of Korea from 2010-2013 and 2020-2023. Over 10 years, FHB fungi developed resistance to demethylation inhibitors (DMIs), methyl benzimidazole carbamates (MBCs), and phthalimides, with few exceptions. Also, no significant resistance against succinate dehydrogenase inhibitors (SDHI) and quinoneoutside inhibitors (QoI) was observed, but sensitivity to phenylpyrrole (PP) increased. Mycotoxin production by four representative isolates of both species indicated that higher doses of DMI, DMI + DMI, MBC, MBC + DMI, and PP controlled trichothecenes, whereas zearalenone was controlled only by SDHI. QoI, QoI + DMI, and phthalimide did not control mycotoxin production in either species. Despite resistance development, DMI, MBC, and PP can still be used to control FHB and mycotoxins in wheat and barley in Korea with close monitoring of resistance.

Keywords: cereals; effective concentration 50%; scab; toxin.

Fig. 1

(A) A map of the Republic of Korea indicating two provinces where the sampling was done. Parenthesized percentages represent distribution of isolates from the respective regions. (B) Distribution of Fusarium asiaticum and F. graminearum isolates by chemotypes at two time periods. Number of isolates obtained in respective chemotype are given above bars. NIV, nivalenol; 3AD, 3-acetyl deoxynivalenol; 15AD, 15-acetyl deoxynivalenol.

Fig. 2

Comparison of sensitivity of Fusarium asiaticum and F. graminearum isolates to 15 fungicide treatments between 2010 and 2020. Asterisk (*) in red indicates significant difference (P ≤ 0.05) in EC₅₀ values between compared time periods within a species. Hash sign (#) followed by year indicate significant difference (P ≤ 0.05) in EC₅₀ values between F. asiaticum and F. graminearum at respective time period. Arrows within each chart represent intuitive comparison of the changes in the slope. The less-than sign “<“ between the species in charts indicate the fungicide treatments for which F. asiaticum isolates showed less mean EC₅₀ values compared to F. graminearum isolates. DMI, demethylation inhibitor; MBC, methyl benzimidazole carbamate; PP, phenylpyrrole; QoI, quinone-outside inhibitor; SDHI, succinate dehydrogenase inhibitors.

Fig. 3

Principal component analysis based on EC₅₀ values of 161 Fusarium asiaticum and F. graminearum isolates against 15 fungicide treatments. Proportion of total variance that can be explained by the first and second principal components are given by RX2 values. Labels in color represent: brown points for F. asiaticum isolates, black triangle points for F. graminearum isolates, and green points for factors including fungicide treatments, plant hosts, year of isolation, province, chemotypes and species.

Fig. 4

Growth (colony diameter) and mycotoxin production by Fusarium asiaticum (R17 & R50), F. graminearum (R05 & R51) at different fungicide concentrations. Alphabetical labels inside each chart represent respective fungicides. (A) Demethylation inhibitor (DMI) and DMI combination fungicides. D, difenoconazole; H, hexaconazole; M, metconazole; P, propiconazole; T, tebuconazole; DP, difenoconazole + propiconazole; PT, propiconazole + tebuconazole; DMI + MBC: PTh, propiconazole + thiophanate-methyl; AH, azoxystrobin + hexaconazole. (B) Non-DMI fungicides. PP fungicide: F, fludioxonil; MBC: Th, thiophanate-methyl; QoI: A, azoxystrobin; Tr, trifloxystrobin; SDHI: Fl, fluxapyroxad; Phthalimides: C, captan. Columns in charts represent growth in terms of colony diameter. Continuous lines across charts represent mycotoxins; 4-ANIV (red), nivalenol (green), 15-ADON (grey), deoxynivalenol (orange), 3-ADON (yellow), and zearalenone (blue). MBC, methyl benzimidazole carbamate; PP, phenylpyrrole; QoI, quinone-outside inhibitor; SDHI, succinate dehydrogenase inhibitors.

Fig. 5

Correlation analyses between fungicide concentration, growth (colony diameter) and mycotoxin production in Fusarium asiaticum (A) and F. graminearum (B). The upper triangle of the plot shows the Spearman’s correlation coefficients for pairs of variables, the diagonal displays density plots, which help understand the distribution of each variable and the lower triangle shows scatterplots to visualize the relationship between variables. Asterisks (*) indicate statistical significance. ***Highly significant (P < 0.001), **Moderate significance (P < 0.01), *Significant (P < 0.05), no asterisk indicate non-significant. DON, deoxynivalenol; NIV, nivalenol; PP, phenylpyrrole; ZEA, zearalenone; 4-ANIV, 4-acetyl nivalenol; 3-ADON, 3-acetyl deoxynivalenol; 15-ADON, 15-acetyl deoxynivalenol.