Resistance to triazole fungicides in Pyricularia species is associated with invasive plants from wheat fields in Brazil

ABSTRACT. Triazole fungicides have not been effective for managing the wheat blast disease in Brazil. A broad analysis across six geographical populations of Pyricularia graminis-tritici in central-southern Brazil indicated a high level of resistance to triazole fungicides. Since P. graminis-tritici is also associated with others poaceous species, here, we analyzed whether triazole-resistant isolates of the blast pathogen could be recovered from other poaceous hosts that are invasive of sprayed wheat fields. In addition to P. graminis-tritici (Pygt), we also evaluated the levels of sensitivity of three other grass-associated blast pathogens, which included P. grisea (Pg), P. pennisetigena (Pp), and P. urashimae (Pu). Resistance to the triazole fungicides tebuconazole and epoxiconazole was assessed phenotypically based on EC50 values and molecularly by analysis of the presence of mutations in the CYP51A gene, which encodes for the target enzyme 14-alpha-demethylase. We detected triazole-resistant Pyricularia spp. (Pg, Pp, Pu and Pygt) that is associated with Avena sativa, Cenchrus echinatus, Chloris distichophylla, Cynodon sp., Digitaria horizontalis, D. sanguinalis, Panicum maximum or Urochloa spp. The major outcome from our study was the evidence that invasive poaceous species from wheat fields could be an important source of triazole resistant fungal inoculum for the initial phases of the wheat blast epidemics.

摘要。三唑类杀菌剂（triazole fungicides）对巴西小麦瘟病的防治效果不佳。针对巴西南部中部的6个小麦瘟病菌（Pyricularia graminis-tritici，简称Pygt）地理种群开展的全面分析结果显示，该病原菌对三唑类杀菌剂具有高水平抗性。由于小麦瘟病菌还可侵染其他禾本科植物，本研究旨在探究喷施过杀菌剂的麦田中的外来禾本科寄主是否可分离得到抗三唑类杀菌剂的瘟病病原菌菌株。除小麦瘟病菌（Pyricularia graminis-tritici，简称Pygt）外，本研究还评估了另外3种与禾草相关的瘟病病原菌的敏感性水平，分别为灰梨孢菌（P. grisea，简称Pg）、狼尾草梨孢菌（P. pennisetigena，简称Pp）以及浦岛梨孢菌（P. urashimae，简称Pu）。本研究通过基于半最大效应浓度（EC50 values）的表型分析，以及对编码靶标酶14-α-脱甲基酶（14-alpha-demethylase）的CYP51A基因的突变检测开展分子分析，以此评估病原菌对戊唑醇（tebuconazole）与环氧菌唑（epoxiconazole）这两种三唑类杀菌剂的抗性水平。本研究从燕麦（Avena sativa）、刺蒺藜草（Cenchrus echinatus）、双叶虎尾草（Chloris distichophylla）、狗牙根属（Cynodon sp.）、横叶马唐（Digitaria horizontalis）、马唐（D. sanguinalis）、大黍（Panicum maximum）以及臂形草属（Urochloa spp.）等寄主中分离得到了抗三唑类杀菌剂的梨孢属真菌菌株（涵盖Pg、Pp、Pu及Pygt）。本研究的核心结论为：麦田中的外来禾本科植物可成为小麦瘟病流行初期阶段抗三唑类杀菌剂真菌接种体（fungal inoculum）的重要来源。