Spatio-temporal distribution of DMI and SDHI fungicide resistance of Zymoseptoria tritici throughout Europe based on frequencies of key target-site alterations.

BACKGROUND: Over the past decade, demethylation inhibitor (DMI) and succinate dehydrogenase inhibitor (SDHI) fungicides have been extensively used to control to septoria tritici blotch, caused by Zymoseptoria tritici on wheat. This has led to the development and selection of alterations in the target-site enzymes (CYP51 and SDH, respectively). RESULTS: Taking advantage of newly and previously developed qPCR assays, the frequency of key alterations associated with DMI (CYP51-S524T) and SDHI (SDHC-T79N/I, C-N86S and C-H152R) resistance was assessed in Z. tritici-infected wheat leaf samples collected from commercial crops (n = 140) across 14 European countries prior to fungicide application in the spring of 2019. This revealed the presence of a West to East gradient in the frequencies of the most common key alterations conferring azole (S524T) and SDHI resistance (T79N and N86S), with the highest frequencies measured in Ireland and Great Britain. These observations were corroborated by sequencing (CYP51 and SDH subunits) and sensitivity phenotyping (prothioconazole-desthio and fluxapyroxad) of Z. tritici isolates collected from a selection of field samples. Additional sampling made at the end of the 2019 season confirmed the continued increase in frequency of the targeted alterations. Investigations on historical leaf DNA samples originating from different European countries revealed that the frequency of all key alterations (except C-T79I) has been gradually increasing over the past decade. CONCLUSION: Whilst these alterations are quickly becoming dominant in Ireland and Great Britain, scope still exists to delay their selection throughout the wider European population, emphasizing the need for the implementation of fungicide antiresistance measures. © 2021 Society of Chemical Industry.

Dynamics of nitrous oxide with depth in groundwater: Insights from ambient groundwater and laboratory incubation experiments (Hesbaye chalk aquifer, Belgium).

Aquifers under agricultural areas are considered to be an indirect source of nitrous oxide emission (N2O) to the atmosphere, which is the greenhouse gas (GHGs) characterized with the highest global warning potential and acts as a stratospheric ozone depletion agent. Previous investigations performed in the Cretaceous Hesbaye chalk aquifer in Eastern Belgium suggested that the dynamics of N2O in the aquifer is controlled by overlapping biochemical processes such as nitrification and denitrification. The current study aims to obtain better insight concerning the factors controlling the distribution of N2O concentration along a vertical dimension in the aquifer, and to capture and quantify the occurrence of nitrification and denitrification processes in the groundwater system. Low-flow groundwater sampling technique was undertaken at different depths in the aquifer to collect groundwater samples aiming at obtaining information about ambient aquifer hydrogeochemical conditions and their effect on the accumulation of GHGs. Afterwards, laboratory stable isotope experiments, using NO3- and NH4+ compounds labeled with heavy 15N isotope, were applied to quantify the rates of nitrification and denitrification processes. Ambient studies suggest that the occurrence of N transformation was related to denitrification while laboratory incubation experiments did not detect it. Such controversial results might be explained by the discrepancy between real aquifer conditions and lab design studies. Thus, additional in situ tracer experiments should be carried out in areas where natural groundwater fluxes do not flush the injected tracer too rapidly. In addition, it would be useful to conduct microbiological studies to obtain better insight into the nature of subsurface biofilm biotope.

Relationship between Fusarium spp. diversity and mycotoxin contents of mature grains in southern Belgium.

Over a 4-year period (2010-13), a survey aiming at determining the occurrence of Fusarium spp. and their relations to mycotoxins in mature grains took place in southern Belgium. The most prevalent species were F. graminearum, F. avenaceum, F. poae and F. culmorum, with large variations between years and locations. An even proportion of mating type found for F. avenaceum, F. culmorum, F. cerealis and F. tricinctum is usually a sign of ongoing sexual recombination. In contrast, an unbalanced proportion of mating type was found for F. poae and no MAT1-2 allele was present in the F. langsethiae population. Genetic chemotyping indicates a majority of deoxynivalenol (DON)-producing strains in F. culmorum (78%, all 3-ADON producers) and F. graminearum (95%, mostly 15-ADON producers), while all F. cerealis strains belong to the nivalenol (NIV) chemotype. Between 2011 and 2013, DON, NIV, enniatins (ENNs) and moniliformin (MON) were found in each field in various concentrations. By comparison, beauvericin (BEA) was scarcely detected and T-2 toxin, zearalenone and α- and ß-zearalenols were never detected. Principal component analysis revealed correlations of DON with F. graminearum, ENNs and MON with F. avenaceum and NIV with F. culmorum, F. cerealis and F. poae. BEA was associated with the presence of F. tricinctum and, to a lesser extent, with the presence of F. poae. The use of genetic chemotype data revealed that DON concentrations were mostly influenced by DON-producing strains of F. graminearum and F. culmorum, whereas the concentrations of NIV were influenced by the number of NIV-producing strains of both species added to the number of F. cerealis and F. poae strains. This study emphasises the need to pay attention to less-studied Fusarium spp. for future Fusarium head blight management strategies, as they commonly co-occur in the field and are associated with a broad spectrum of mycotoxins.