BACKGROUND: Fusarium asiaticum is one of predominant pathogens of Fusarium head blight (FHB) in China. Pydiflumetofen (Pyd) is a novel succinate dehydrogenase inhibitor (SDHI) which has been commercialized in China for the controlling of wheat FHB since 2019. In the current study, a risk assessment of the pydiflumetofen-resistance selected in Fusarium asiaticum was investigated. RESULTS: One Pyd MR mutant [resistance factor (RF) < 80] and four Pyd HR mutants (RF > 3000) were generated by fungicidetaming from 1000 mycelial discs of the wild-type strain 2021. Nucleotide sequences alignment results of FaSdh from the wild-type strain and resistant mutants showed that all the mutations were categorized into three genotypes, i.e. FaSdhB H248Y from Pyd MR mutant, both FaSdhC 1 A64V and FaSdhC 1 R67K from Pyd HR mutants. All the resistant mutants possessed no fitness penalty based on the data of mycelial linear growth, conidiation and virulence. In addition, the FaSdhC 1 A64V mutants showed positive cross-resistance between pydiflumetofen and boscalid or thifluzamide, but no cross-resistance between pydiflumetofen and Y13149 or Y12196, while the FaSdhC 1 R67K mutants exhibited positive cross-resistance between pydiflumetofen and boscalid, thifluzamide or Y12196, and no cross-resistance between pydiflumetofen and Y13149. Furthermore, positive cross-resistance between the five tested SDHIs was detected in the FaSdhB H248Y mutants. CONCLUSION: The results suggest a moderate to high resistance risk of F. asiaticum to pydiflumetofen, and provide essential data for monitoring the emergence of resistance and resistance management strategies for pydiflumetofen, which will be useful for scientific application of this fungicide in China.
Fusarium graminearum is one of the phytopathogenic fungi causing cereal fusarium head blight worldwide. Flubeneteram (Flu) is a novel succinate dehydrogenase inhibitor (SDHI) which exhibits strong fungicidal activity against F. graminearum. In this study, four Flu-resistant (FluR) mutants were generated by fungicide domestication from the wildtype strain PH-1. Sequencing alignment results of FgSdh from PH-1 and FluR mutants showed that all the mutations could be categorized into three resistant genotypes. Genotype I had an A-to-T mutation at the −57 bp of the 5′ untranslated region (5′UTR) of FgSdhC 1 , while genotypes II and III carried nonsynonymous mutations conferring T77I or R86C in FgSdhC 2 , respectively. All the mutations conferring the Flu resistance and causing fitness penalty were validated. The genotype I mutant showed high Flu-resistance, while genotype II and III mutants exhibited low Flu resistance. Additionally, all the FluR genotypes showed distinct cross-resistance patterns among the five SDHIs.
Garlic leaf blight (GLB) caused by Stemphylium eturmiunum is first reported in Jiangsu Province of China. The dicarboximide fungicide (DCF) procymidone is reported to possess broad-spectrum action in inhibiting filamentous fungi and widely used to control leaf disease of various plants. In current study, of 41 S. eturmiunum isolates collected from commercial garlic farms in Pizhou and Dafeng Counties of Jiangsu Province, eight isolates were resistant to procymidone. Three phenotypes were categorized according to the in vitro responses to dicarboximide fungicides: S (sensitive), S+ (LR to iprodione and procymidone), and R2 (HR to all iprodione and procymidone). The fitness of all the resistant isolates was decreased in accordance with the data of mycelial growth, conidiation and virulence. After treated with 10µg/ml procymidone for 4 h, mycelial intracellular glycerol concentrations of resistant isolates were significantly lower than those of sensitive isolates. Positive cross-resistance was observed between dicarboximides and phenylpyrroles, but no cross-resistance between dicarboximides and fluazinam or difenoconazole in the two resistant phenotypes. Nucleotide sequence alignment results of the two-component histidine kinase genes from the sensitive and resistant isolates indicated that amino acid mutations were located at the histidine kinase, adenylyl cyclase, methyl-accepting chemotaxis protein, and phosphatase (HAMP) domain of N-terminal region, and response regulator domain (Rec) of C-terminal region. To our knowledge, the DCF-resistance in S. eturmiunum is first reported, and the findings are helpful to establish the rational strategy to manage the DCF-resistant populations of S. eturmiunum in field.
Alternaria alternata, a causal agent of leaf blights and spots on a wide range of hosts, has a high risk of developing resistance to fungicides. Procymidone, a dicarboximide fungicide (DCF), has been widely used in controlling Alternaria leaf blights in China for decades. However, the resistance of A. alternata against DCFs has rarely been reported from crucifer plants. A total of 198 A. alternata isolates were collected from commercial fields of broccoli and cabbage during 2018–2019, and their sensitivities to procymidone were determined. Biochemical and molecular characteristics were subsequently compared between the high-level procymidone-resistant (ProHR) and procymidone-sensitive (ProS) isolates, and also between ProHR isolates from broccoli and cabbage. Compared with ProS isolates, the mycelial growth rate, sporulation capacity and virulence of most ProHR isolates were reduced; ProHR isolates displayed an increased sensitivity to osmotic stresses and a reduced sensitivity to sodium dodecyl sulfate (SDS); all ProHR isolates showed a reduced sensitivity to hydrogen peroxide (H2O2) except for the isolate B102. Correlation analysis revealed a positive cross-resistance between procymidone and iprodione, or fludioxonil. When treated with 10 μg/mL of procymidone, both mycelial intracellular glycerol accumulations (MIGAs) and relative expression of AaHK1 in ProS isolates were higher than those in ProHR isolates. Sequence alignment of AaHK1 from ten ProHR isolates demonstrated that five of them possessed a single-point mutation (P94A, V612L, E708K or Q924STOP), and four isolates had an insertion or a deletion in their coding regions. No significant difference in biochemical characteristics was observed among ProHR isolates from two different hosts, though mutations in AaHK1 of the cabbage-originated ProHR isolates were distinct from those of the broccoli-originated ProHR isolates.
Black spots caused by Alternaria Alternata poses a sever threat to the industry of Dendrobium officinale, a Chinese indigenous medicinal herb. Dicarboximide fungicides (DCFs) are intensively used to control this disease for decades in China, and offering excellent efficacy. The resistance of phytopathogenic pathogens against DCFs are reportedly selected in fields; however, the DCF-resistance of A. alternata from D. officinale is not well understood. The low procymidone-resistant (ProLR) isolates of A. alternata were detected in the commercial orchards of D. officinale in China in 2018 and biochemically characterized in this study. The result showed that the low procymidone-resistant (ProLR) isolates were selected in the commercial orchards with the resistance frequency of 100 %, and no significant difference in mycelial growth, sporulation and virulence was observed among the ProLR and ProS isolates. A positive cross-resistance pattern was exhibited between procymidone and iprodione. Amino acid sequence alignment results of AaOS-1 from the tested isolates showed that all the ProLR genotypes could be categorized into two groups, including group I (mutations at AaOs-1) and group II (no mutation). On procymidone (5.0 μg/ml) treatment condition, the AaOs-1 expression levels increased in the ProS isolates ranged from 2.94~3.69 folds higher than those on procymidone-free condition, while the AaOs-1 expressions of the ProLR isolates were significantly lower than those in the ProS isolates on the same conditions. The data indicated that the mutations at AaOs-1 are involved in the DCF-resistance of A. alternata selected in the D. officinale orchards.
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