SDHI resistance in Pyrenophora teres f teres and molecular detection of novel double mutations in sdh genes conferring high resistance

Abstract

BACKGROUND: Net blotch (NB), caused by Pyrenophora teres f. teres (Ptt), is an important disease of barley worldwide. NB control is commonly achieved through the use of fungicide mixtures including strobilurins, triazoles and carboxamides. Succinate dehydrogenase inhibitors (SDHI) are important components of fungicide management programs of barley diseases. However, during the last growing seasons in Argentina, barley fields sprayed with mixtures containing SDHI fungicides have shown failures in NB control. Here, we report the isolation and characterization of Argentine Ptt strains resistant to SDHI fungicides.RESULTS: Compared against a sensitive (wild-type) reference strain collected in 2008, all 21 Ptt isolates collected in 2021 exhibited resistance to pydiflumetofen and fluxapyroxad both in vitro and in vivo. Concordantly, all of them presented target-site mutations in any of the sdhB, sdhC and sdhD genes. Although the mutations detected have been previously reported in other parts of the world, this study documents for the first time the occurrence of double mutations in the same Ptt isolate. Specifically, the double mutation sdhC-N75S + sdhD-D145G confers high resistance to SDHI fungicides, while the double mutations sdhB-H277Y + sdhC-N75S and sdhB-H277Y + sdhC-H134R confer moderate levels of resistance in Ptt.CONCLUSIONS: SDHI-resistance in Argentine Ptt populations is expected to increase. These findings emphasize the urgent need to perform a wider survey and a more frequent monitoring of SDHI sensitivity of Ptt populations and to develop and implement effective antiresistance tactics.

Fungicide Sensitivity Profile of Pyrenophora teres f. teres in Field Population

“…In the current study, out of these only mutations, C-S135R and D-H134R were identified in the Ptt population, and 30% of the Ptt isolates collected in 2021 and 40% in 2022 were mutated. Mutation B-H277Y, which has been found in other countries [21,36], was absent in the Estonian Ptt population. The fluxapyroxad and bixafen sensitivity were both affected in the SDH-mutated Ptt isolates in Estonia.…”

“…Higher resistance factors have been associated with mutations C-G79R, D-H134R, D-D124E, and C-H134R, with reduced fluxapyroxad efficacy [21,35]. In Argentina, the detection of Ptt isolates carrying double mutation C-N75S + D-D145G raises concerns in fluxapyroxad field efficacy [36]. As fluxapyroxadcontaining products (e.g., Priaxor and Revytrex by BASF) are often used in cereal disease control and the spread of SDH-mutated Ptt isolates within the Estonian population is remarkable, the field efficacy should be monitored.…”

“…The sequences obtained were analysed, and the target-site mutations were identified using blastn and blastx search tools (https://blast.ncbi.nlm.nih.gov/Blast.cgi (accessed 21 December 2023)) available at NCBI. We focused on previously published relevant SNPs in the target protein-coding gene sequences associated with fungicide insensitivity [19,21,[34][35][36]. The representative sequences of the fungicide target protein genes of the studied Ptt isolates are deposited in NCBI GenBank with accession numbers OR530176, OR761967 to OR761973, and OR777246 to OR777248 (Table S1).…”

“…In this first comprehensive study of the Estonian Ptt population, we focused on the current status of fungicide sensitivity and its association with relevant SNPs in target protein-coding gene sequences linked to fungicide insensitivity [19,21,[34][35][36]. Therefore, the objectives of this research were to assess the Estonian Ptt population for (i) fungicide sensitivity level in vitro microtiter plate assays and subsequently associate insensitivity with (ii) Cyt b mutations, (iii) SDH subunit mutations, (iv) molecular changes in the Cyp51A gene and promoter region; and (v) potential sexual recombination by the analysing mating type prevalence rate.…”

Resistance risk assessment for benzovindiflupyr in Sclerotium rolfsii and transmission of resistance genes among population

“…This mutation was equivalent to the SdhD H132R in Sclerotinia sclerotiorum and Botrytis cinerea, and SdhD H134R in Pyrenophora teres f. teres, which were verified to confer SDHI resistance in previous studies. 30,32,33 It should be noted that SdhD H103Y was a heterozygous mutation (still containing the wild-type SdhD allele) in Sclerotium rolfsii, and these heterokaryotic resistant isolates were moderately resistant to benzovindiflupyr in this study. We speculate that this phenomenon is dependent on the nuclear resistant allele proportion, because other studies found that homokaryotic mutants of R. solani and Sclerotinia sclerotiorum commonly showed higher resistance to thifluzamide than heterozygous mutants.…”