Gray mold, caused by the fungus Botrytis cinerea, is one of the most important diseases of strawberry in Germany. The application of site-specific fungicides remains the main strategy to reduce ...disease incidence and severity in the field. Isolates (n = 199) were collected from fungicide-treated strawberry fruit at a German research site with a long history of fungicide efficacy trials against gray mold. Sensitivities to the six site-specific botryticides registered in Germany were determined using microtiter assays. Values for the concentration of a fungicide at which fungal development is inhibited by 50% (EC
) ranged from 0.03 to ≥30 ppm for the succinate dehydrogenase inhibitor boscalid, 0.015 to ≥10 ppm for the hydroxyanilide fenhexamid, 0.009 to 0.739 ppm for the phenylpyrrole fludioxonil, 0.55 to 43.45 ppm for the dicarboximide iprodione, 0.021 to ≥3 ppm for the quinone outside inhibitor pyraclostrobin, and 0.106 to ≥30 ppm for the anilinopyrimidine pyrimethanil. Pyrosequencing revealed that amino acid substitutions in the target proteins Bos1 (I365S/N, V368F + Q369H), CytB (G143A), Erg27 (F412S), and SdhB (P225F, N230I, and H272R/Y) were associated with reduced sensitivity levels to the corresponding fungicide classes. In most cases, isolates with a decreased sensitivity to fludioxonil showed a reduced sensitivity to tolnaftate. This reduction is considered to be an indication of multidrug efflux pump activity. The amino acid change I365S, I365N, or V368F + Q369H in Bos1 and H272R in SdhB by itself showed EC
values of 3.99 to 14.73 ppm, 3.87 to 5.37 ppm, 4.81 to 15.63 ppm, and 2.071 to ≥30 ppm, respectively. When isolates that contained one of these mutations were also multidrug resistant, the ranges of EC
values shifted to 6.47 to 43.45 ppm for I365S, 7.28 to 29.84 ppm for I365N, 6.89 to 26.67 ppm for V368F + Q369H, and ≥30 ppm for H272R. The reported data suggest that the combination of multidrug resistance and an amino acid change in the target site may result in a lower sensitivity to the fungicides than one resistance mechanism by itself. Although 20% of the population analyzed was sensitive to all six different chemical classes, the majority showed reduced sensitivity to one (6%), two (13%), three (23%), four (17%), five (11%), and six (11%) different fungicides.
Septoria tritici blotch (STB;
) is a severe leaf disease on wheat in Northern Europe. Fungicide resistance in the populations of
is increasingly challenging future control options. Twenty-five field ...trials were carried out in nine countries across Europe from 2019 to 2021 to investigate the efficacy of specific DMI and SDHI fungicides against STB. During the test period, two single DMIs (prothioconazole and mefentrifluconazole) and four different SDHIs (fluxapyroxad, bixafen, benzovindiflupyr and fluopyram) along with different co-formulations of DMIs and SDHIs applied at flag leaf emergence were tested. Across all countries, significant differences in azole performances against STB were seen; prothioconazole was outperformed in all countries by mefentrifluconazole. The effects also varied substantially between the SDHIs, with fluxapyroxad providing the best efficacy overall, while the performance of fluopyram was inferior to other SDHIs. In Ireland and the UK, the efficacy of SDHIs was significantly lower compared with results from continental Europe. This reduction in performances from both DMIs and SDHIs was reflected in yield responses and also linked to decreased sensitivity of
isolates measured as EC
values. A clear and significant gradient in EC
values was seen across Europe. The lower sensitivity to SDHIs in Ireland and the UK was coincident with the prevalence of SDH-C-alterations T79N, N86S, and sporadically of H152R. The isolates' sensitivity to SDHIs showed a clear cross-resistance between fluxapyroxad, bixafen, benzovindiflupyr and fluopyram, although the links with the latter were less apparent. Co-formulations of DMIs + SDHIs performed well in all trials conducted in 2021. Only minor differences were seen between fluxapyroxad + mefentrifluconazole and bixafen + fluopyram + prothioconazole; the combination of benzovindiflupyr + prothioconazole gave an inferior performance at some sites. Fenpicoxamid performed in line with the most effective co-formulations. This investigation shows a clear link between reduced field efficacy by solo SDHIs as a result of increasing problems with sensitivity shifting and the selection of several SDH-C mutations. The presented data stress the need to practice anti-resistance strategies to delay further erosion of fungicide efficacy.
Net blotch of barley caused by
Pyrenophora teres
(Died.) Drechsler, is one of the most destructive diseases on barley in Algeria. It occurs in two forms:
P. teres
f.
teres
and
P. teres
f.
maculata
. ...A total of 212 isolates, obtained from 58 fields sampled in several barley growing areas, were assessed for fungicide sensitivity by target gene analysis. F129L and G137R mitochondrial cytochrome
b
substitution associated with quinone outside inhibitors (QoIs) resistance, and succinate dehydrogenase inhibitors (SDHIs) related mutations (B-H277, C-N75S, C-G79R, C-H134R, and C-S135R), were analyzed by pyrosequencing.
In vitro
sensitivity of 45 isolates, towards six fungicides belonging to three chemical groups (QoI, demethylase inhibitor, and SDHI) was tested by microtiter technique. Additionally, sensitivity towards three fungicides (azoxystrobin, fluxapyroxad, and epoxiconazole) was assessed
in planta
under glasshouse conditions. All tested isolates were QoI-sensitive and SDHI-sensitive, no mutation that confers resistance was identified. EC50 values showed that pyraclostrobin and azoxystrobin are the most efficient fungicides
in vitro
, whereas fluxapyroxad displayed the best disease inhibition
in planta
(81% inhibition at 1/9 of the full dose). The EC
50
values recorded for each form of net blotch showed no significant difference in efficiency of QoI treatments and propiconazole on each form. However, in the case of fluxapyroxad, epoxiconazole and tebuconazole treatments, analysis showed significant differences in their efficiency. To our knowledge, this study is the first investigation related to mutations associated to QoI and SDHI fungicide resistance in Algerian
P. teres
population, as well as it is the first evaluation of the sensitivity of
P. teres
population towards these six fungicides.
Net blotch of barley caused by Pyrenophora teres (Died.) Drechsler, is one of the most destructive diseases on barley in Algeria. It occurs in two forms: P. teres f. teres and P. teres f. maculata. A ...total of 212 isolates, obtained from 58 fields sampled in several barley growing areas, were assessed for fungicide sensitivity by target gene analysis. F129L and G137R mitochondrial cytochrome b substitution associated with quinone outside inhibitors (QoIs) resistance, and succinate dehydrogenase inhibitors (SDHIs) related mutations (B-H277, C-N75S, C-G79R, C-H134R, and C-S135R), were analyzed by pyrosequencing. In vitro sensitivity of 45 isolates, towards six fungicides belonging to three chemical groups (QoI, demethylase inhibitor, and SDHI) was tested by microtiter technique. Additionally, sensitivity towards three fungicides (azoxystrobin, fluxapyroxad, and epoxiconazole) was assessed in planta under glasshouse conditions. All tested isolates were QoI-sensitive and SDHI-sensitive, no mutation that confers resistance was identified. EC50 values showed that pyraclostrobin and azoxystrobin are the most efficient fungicides in vitro, whereas fluxapyroxad displayed the best disease inhibition in planta (81% inhibition at 1/9 of the full dose). The EC50 values recorded for each form of net blotch showed no significant difference in efficiency of QoI treatments and propiconazole on each form. However, in the case of fluxapyroxad, epoxiconazole and tebuconazole treatments, analysis showed significant differences in their efficiency. To our knowledge, this study is the first investigation related to mutations associated to QoI and SDHI fungicide resistance in Algerian P. teres population, as well as it is the first evaluation of the sensitivity of P. teres population towards these six fungicides.
Succinate dehydrogenase inhibitors (SDHIs) are an important group of fungicides (FRAC Group 7) for the control of
Venturia inaequalis
. Mechanisms which lead to reduced SDHI sensitivity in fungi are ...based on mutations in the SDH-subunits B, C, or D of the target gene. Monitoring studies have shown that most of the European population is still sensitive to SDHIs. Single cases of SDHI resistance have been detected shortly after market introduction although mainly at trial sites. The underlying resistance mechanisms have been identified as target site mutations (B-T258I, C-N85S and C-H151R). However, these were single findings which did not increase in frequency or even disappeared when the same field was analyzed one or more seasons later. This is in contrast to findings on other resistance cases which are stable over several seasons even without selection pressure, such as QoI and benzimidazole resistance. High frequencies of target site mutations for QoIs and benzimidazoles (G143A and E198A, respectively) have been detected in a 2022 survey, whereas no SDHI target site mutation exceeded the detection limit of our molecular detection assay in any sample.
Asian soybean rust (ASR), caused by the fungus Phakopsora pachyrhizi Syd & P. Syd, is the main disease that affects soybean crop in South America. Disease control is based on the use of site-specific ...fungicides (QoIs, DMIs and SDHIs), multisite fungicides and host-free period. Continuous and intensive use of fungicides has selected isolates of P. pachyrhizi, with reduced sensitivity to DMIs, QoIs and SDHIs. This work includes sensitivity studies for prothioconazole and SDHIs and genetic analysis of target site mutations in P. pachyrhizi related to sensitivity reduction to DMIs, QoIs and SDHIs collected from different regions of soybean production areas. Different CYP51 genotypes with distinct point mutations known to influence DMI sensitivity are present in Brazilian isolates. Combined mutation F120L + Y131H on CYP51 gene was the most frequent among Brazilian isolates. Mutant isolates showed higher EC50 values to the DMI prothioconazole compared to wild type isolates. Regarding QoI, almost all Brazilian isolates carried the mutation F129L in the CYTB gene. Wild type of the SdhC gene was the most frequent genotype to SDHI fungicides, but the mutation leading to the I86F amino acid exchange has also been detected. Such isolates showed higher EC50 values to the SDHIs bixafen, benzovindiflupyr and fluxapyroxad compared to wild type isolates. The most frequent genotype in our collection presented target site mutations in the CYP51 and CYTB genes. A monouredinial isolate with mutations in all three target genes was detected and is here described for the first time. Its current and further spread, and the impact on field performance of fungicides with these modes of action needs further evaluation.
Display omitted
•Multiple resistance Phakopsora pachyrhizi monouredinial isolate is first described.•Mutation F120L + Y131H on the CYP51 gene was the most frequent.•90% of the samples carried CYTB F129L alleles.•Wild type of the SdhC gene were the most frequent genotype to SDHI fungicides.
Ramularia collo-cygni is a devastating plant pathogen of barley with an increasing importance in Europe and several other barley growing regions worldwide. R. collo-cygni is a pathogen with potential ...to adapt rapidly to environmental changes and is classified as a “high-risk” phytopathogen with respect to the evolution of fungicide resistance. Quinone-outside inhibitors (QoIs), demethylation inhibitors (DMIs) and succinate dehydrogenase inhibitors (SDHIs) represent three major fungicide classes that are frequently used to control a broad range of relevant cereal pathogens. However, in recent years R. collo-cygni has acquired resistance to QoIs; in addition reduced efficacy of SDHI-and DMI-containing products has been observed. In this study, we have investigated the frequency of SDHI-and DMI-adapted isolates in a European population of R. collo-cygni and evaluated the underlying resistance mechanisms towards both fungicide classes. Several mutations in the target genes of SDHIs were detected in the population of R. collo-cygni under investigation (B-H266Y/R, B-T267I, B-I268V, C-N87S, C-H146R, C-H153R and some others) with increasing frequencies since 2014. SDHI resistance in R. collo-cygni is mainly driven by both the presence of mutations and the high frequency of such mutations in the population. Additionally, DMI-adapted isolates of R. collo-cygni were found at a high frequency in the countries under investigation. Fifteen different Cyp51 haplotypes were detected in the set of isolates from 2009 to 2017. The most frequent haplotype in 2017 was C1 haplotype, which comprises three mutations in Cyp51 and shows a substantial increase in EC₅₀ values to DMIs compared with other isolates. As R. collo-cygni has adapted to several groups of fungicides in many regions in Western Europe, future control of this highly diverse and adaptable pathogen must focus on new molecules, choosing resistant varieties and the improvement in seed hygiene standards.
PDF
