Widespread distribution of resistance to triazole fungicides in Brazilian populations of the wheat blast pathogen,Plant Pathology

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Widespread distribution of resistance to triazole fungicides in Brazilian populations of the wheat blast pathogen
Plant Pathology ( IF 2.3 ) Pub Date : 2020-10-28 , DOI: 10.1111/ppa.13288
N.M. Poloni ₁ , G. Carvalho ₁ , S.N.C. Vicentini ₁ , A.F. Dorigan ₁ , J.L.N. Maciel ₂ , B.A. McDonald ₃ , S.I. Moreira ₁ , N. Hawkins ₄ , B.A. Fraaije _{4,

5} , D.E. Kelly ₆ , S.L. Kelly ₆ , P.C. Ceresini ₁

Affiliation

Fungicides have not been effective in controlling the wheat blast disease in Brazil. An earlier analysis of 179 isolates of Pyricularia oryzae Triticum lineage (PoTl) sampled from wheat fields across six populations in central‐southern Brazil during 2012 discovered a high level of resistance to strobilurin fungicides. Here we analysed azole resistance in the same strains based on EC50 measurements for tebuconazole and epoxiconazole. All six Brazilian populations of PoTl exhibited high resistance to both azoles, with in vitro EC50 values that were at least 35 to 50 times higher than the recommended field doses. We sequenced the CYP51A and CYP51B genes to determine if they were likely to play a role in the observed azole resistance. Although we found five distinct haplotypes in PoTl carrying four nonsynonymous substitutions in CYP51A, none of these substitutions were correlated with elevated EC50. CYP51B was sequenced for nine PoTl isolates, three each representing low, medium, and high tebuconazole EC50. Both PoTl CYP51A and CYP51B could complement yeast CYP51 function. All PoTl CYP51A‐expressing yeast transformants were less sensitive to triazoles than the PoTl CYP51B ones. Transformants expressing PoTl CYP51A haplotype H1 carrying the R158K substitution were not more resistant than those expressing PoTl CYP51A haplotype H5, which is synonymous to haplotype H6, found in triazole‐sensitive P. oryzae Oryza isolates from rice blast. Therefore, the reduced triazole sensitivity of wheat blast isolates compared to rice blast isolates appears to be associated with a non‐target‐site related resistance mechanism acquired after higher exposure to triazoles.

中文翻译：

巴西小麦稻瘟病菌种群对三唑类杀菌剂的抗性广泛分布

在巴西，杀菌剂在控制小麦稻瘟病方面没有效果。2012 年，对从巴西中南部六个种群的麦田中取样的 179 株稻瘟病菌谱系 (PoTl) 分离株进行的早期分析发现，对嗜球果伞素杀真菌剂具有高度抗性。在这里，我们根据戊唑醇和氧唑菌的 EC50 测量值分析了相同菌株的唑类抗性。所有六个巴西 PoT1 种群对两种唑类都表现出高抗性，体外 EC50 值至少比推荐的现场剂量高 35 到 50 倍。我们对 CYP51A 和 CYP51B 基因进行了测序，以确定它们是否可能在观察到的唑类耐药性中起作用。尽管我们在 PoTl 中发现了 5 个不同的单倍型，它们在 CYP51A 中携带了 4 个非同义替换，这些取代中没有一个与升高的 EC50 相关。对九个 PoT1 分离株的 CYP51B 进行了测序，三个分别代表低、中和高戊唑醇 EC50。PoT1 CYP51A 和 CYP51B 都可以补充酵母 CYP51 的功能。所有表达 PoTl CYP51A 的酵母转化体对三唑类药物的敏感性均低于 PoTl CYP51B。表达携带 R158K 取代的 PoTl CYP51A 单倍型 H1 的转化子并不比表达 PoTl CYP51A 单倍型 H5 的那些具有更强的抗性，后者与单倍型 H6 同义，存在于稻瘟病的三唑敏感稻瘟病菌分离株中。因此，与稻瘟病株相比，小麦瘟疫株对三唑类药物的敏感性降低似乎与更高程度接触三唑类药物后获得的非靶点相关抗性机制有关。

更新日期：2020-10-28

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