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BACKGROUND: Septoria tritici blotch caused by Zymoseptoria tritici continues to be one of the most economically destructive diseases of winter wheat in north‐western Europe. Control is heavily reliant on the application of fungicides, in particular those belonging to the azole group. Here we describe the sensitivity of European Z. tritici populations to the novel azole mefentrifluconazole and the analysis of associated mechanisms of resistance. RESULTS: A wide range of sensitivity to mefentrifluconazole was observed amongst the Z. tritici collections examined, with strong cross‐resistances also observed between mefentrifluconazole, difenoconazole and tebuconazole. Overall, the Irish population displayed the lowest sensitivity to all azoles tested. Further detailed analysis of the Irish population in 2021 demonstrated differences in sensitivity occurred between sampling sites, with these differences associated with the frequencies of key resistance mechanisms (CYP51 alterations and MFS1 promoter inserts linked to overexpression). Under glasshouse conditions reductions in the efficacy of mefentrifluconazole were observed towards those strains exhibiting the lowest in vitro sensitivities. CONCLUSIONS: This study demonstrates that a large range of sensitivity to mefentrifluconazole exists in European Z. tritici populations. Those strains exhibiting the lowest sensitivity to the azoles tested had the most complex CYP51 haplotypes in combination with the 519 bp insert, associated with enhanced activity of MFS1. The future use of mefentrifluconazole should take these findings into consideration to minimise the selection of these strains. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Research to identify appropriate biological agents for controlling pathogens might exploit experimental evolution to select for enhanced antagonism against pathogens. We developed an experimental regime facilitating this approach, featuring the bacterial broad‐spectrum predator Myxococcus xanthus and the fungal wheat pathogen Zymoseptoria tritici. We demonstrate that Z. tritici, a major cause of crop loss and fungicide use worldwide, both fuels growth of and is killed by M. xanthus on wheat straw, a probable source of seedling infection. M. xanthus was found capable of growth on moistened straw alone, unaided by Z. tritici, in a manner dependent on both M. xanthus initial density and on how long straw was moistened before M. xanthus inoculation. Such growth of non‐cellulolytic myxobacteria on plant detritus may have implications for understanding their roles in nutrient cycling. However, straw with Z. tritici was found to fuel greater M. xanthus growth than straw alone under many conditions. After shorter moistening periods, growth by low‐density M. xanthus populations was found to be fully dependent on Z. tritici. Such pathogen‐dependent M. xanthus populations could be sustained with population replacement over five 1‐week growth cycles, indicating the feasibility of conducting long‐term experimental evolution with this system. Furthermore, M. xanthus was found to kill majorities of Z. tritici populations on both buffered agar and straw. Our results suggest that myxobacteria may serve as effective biocontrol agents of Z. tritici and are amenable to long‐term experimental selection for enhanced killing of this pathogen, an approach broadly applicable to many potential biocontrol agents and target pathogens. [ABSTRACT FROM AUTHOR]

Septoria tritici blotch (STB) is one of the main causes of wheat yield loss in the world. Apart from good agrotechnical practice, disease‐resistant cultivars are required to prevent yield losses. Breeding of such cultivars is time‐consuming and laborious, mainly due to the quantitative character of such resistance, but can be shortened using precise phenotyping. We show that fluorescence parameters, collected in a high‐throughput system, can be used for estimating wheat STB resistance. Using machine learning methods (deep learning network, random forest), we demonstrate that disease resistance based on the percentage of necrotic leaf area can be estimated by alterations in fluorescence parameters 8 days after inoculation, and before disease symptoms become visible. Moreover, we applied a random forest classifier to assess the significance of fluorescence parameters in an informative way (classification accuracy = 64.84%, p value [Accuracy >No information rate] <0.001). Based on this, we observed extensive alterations in parameters of sensitive cultivars, reflecting worse photosynthetic performance. The most highly altered parameters were fluorescence intensity measurements and descriptors of energy flux through photosystem II (PSII) reaction centres towards PSI such as F2, F3 and F4 fluorescence intensities at 0.1, 0.270 and 2 ms; initial to maximal fluorescence ratio (F0/Fm); the time derivative of relative variable fluorescence (dV/dT0); maximum quantum yield of PSII in the dark‐adapted state (Fv/Fm); maximum electron transport flux at PSII (ET0/RC); maximum trapped excitonic energy flux per excited PSII cross section (CS) at time T0 (TR0/CS0); and quantum efficiency of the reduction of end acceptors dR0 [dR0/(1 − dR0)]. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]