Abstract：
BACKGROUND: Litchi downy blight, caused by Phytophthora litchii, is one of the most important diseases of litchi. Ametoctradin, as the only QioI (quinone inside and outside inhibitor) fungicide, has been registered in China in 2019. However, the ametoctradin-resistance risk and molecular basis in Phytophthora litchii have not been reported.
RESULTS: In this study, the sensitivity profile of 144 Phytophthora litchii strains to ametoctradin was determined, with a mean median effective concentration (EC50 ) value of 0.1706 ± 0.091 μg mL-1 . Nine stable resistant Phytophthora litchii mutants [resistance factor (RF) > 400] were derived from sensitive isolates using fungicide adaption. The compound fitness index of three resistant-mutants (HN10-1-1, HN10-1-2 and HN10-2-1) was similar or higher than that of their parental isolates in vitro. All these ametoctradin-resistant mutants were sensitive to metalaxyl, dimethomorph, oxathiapiprolin and cyazofamid. Two point mutations, leading to the S33L and D228N changes in PlCyt b (cytochrome b) were found in ametoctradin-resistant mutants. Eight ametoctradin-resistant mutants containing S33L showed increased sensitivity to azoxystrobin and amisulbrom, and one mutant containing D228N exhibited increased sensitivity to cyazofamid. In vitro enzyme activity test showed that ametoctradin could not inhibit the activity of cytochrome bc1 complex with S33L and D228N point mutation. AS-PCR primers were designed based on the S33L change to detect the ametoctradin-resistant strains in the future.
CONCLUSIONS: These results suggest that Phytophthora litchii has a medium to high resistance risk to ametoctradin in the laboratory. Two changes, S33L and D228N, in PlCyt b are likely to be associated with the observed ametoctradin resistance. © 2022 Society of Chemical Industry.
RESULTS: In this study, the sensitivity profile of 144 Phytophthora litchii strains to ametoctradin was determined, with a mean median effective concentration (EC50 ) value of 0.1706 ± 0.091 μg mL-1 . Nine stable resistant Phytophthora litchii mutants [resistance factor (RF) > 400] were derived from sensitive isolates using fungicide adaption. The compound fitness index of three resistant-mutants (HN10-1-1, HN10-1-2 and HN10-2-1) was similar or higher than that of their parental isolates in vitro. All these ametoctradin-resistant mutants were sensitive to metalaxyl, dimethomorph, oxathiapiprolin and cyazofamid. Two point mutations, leading to the S33L and D228N changes in PlCyt b (cytochrome b) were found in ametoctradin-resistant mutants. Eight ametoctradin-resistant mutants containing S33L showed increased sensitivity to azoxystrobin and amisulbrom, and one mutant containing D228N exhibited increased sensitivity to cyazofamid. In vitro enzyme activity test showed that ametoctradin could not inhibit the activity of cytochrome bc1 complex with S33L and D228N point mutation. AS-PCR primers were designed based on the S33L change to detect the ametoctradin-resistant strains in the future.
CONCLUSIONS: These results suggest that Phytophthora litchii has a medium to high resistance risk to ametoctradin in the laboratory. Two changes, S33L and D228N, in PlCyt b are likely to be associated with the observed ametoctradin resistance. © 2022 Society of Chemical Industry.
摘要：
背景：荔枝枯萎病，由李奇疫霉引起的，是荔枝最重要的疾病之一。Ametoctradin,作为唯一的QioI（醌内外抑制剂）杀菌剂，已于2019年在中国注册。然而,尚未报道在李氏疫霉中的抗阿霉素的风险和分子基础。
结果：在这项研究中，确定了144个李氏疫霉菌株对阿糖胞苷的敏感性，平均中位有效浓度（EC50）值为0.1706±0.091μgmL-1。使用杀菌剂适应性从敏感的分离株中获得了9个稳定的抗性李氏疫霉突变体[抗性因子（RF）>400]。三种抗性突变体（HN10-1-1，HN10-1-2和HN10-2-1）的复合适应度指数在体外相似或高于其亲本分离株。所有这些抗氨色拉素的突变体都对甲霜灵敏感，烯酰吗啉,氧硫哌林和氰胺酮。两个点突变,在抗阿糖胞苷突变体中发现了导致PlCytb（细胞色素b）中S33L和D228N的变化。8个含有S33L的抗阿糖胞苷突变体显示对唑菌酯和氨硫霉素的敏感性增加，和一个含有D228N的突变体显示出对环磷酰胺的敏感性增加。体外酶活性试验表明，氨酰苦素不能抑制S33L和D228N点突变的细胞色素bc1复合物的活性。根据S33L的变化设计AS-PCR引物，以检测抗氨黄碱的菌株。
结论：这些结果表明，在实验室中，李氏疫霉对氨精苷具有中等至高的抗性风险。两个变化，S33L和D228N,在PlCytb中可能与观察到的阿糖胞苷耐药性有关。©2022化学工业学会。
结果：在这项研究中，确定了144个李氏疫霉菌株对阿糖胞苷的敏感性，平均中位有效浓度（EC50）值为0.1706±0.091μgmL-1。使用杀菌剂适应性从敏感的分离株中获得了9个稳定的抗性李氏疫霉突变体[抗性因子（RF）>400]。三种抗性突变体（HN10-1-1，HN10-1-2和HN10-2-1）的复合适应度指数在体外相似或高于其亲本分离株。所有这些抗氨色拉素的突变体都对甲霜灵敏感，烯酰吗啉,氧硫哌林和氰胺酮。两个点突变,在抗阿糖胞苷突变体中发现了导致PlCytb（细胞色素b）中S33L和D228N的变化。8个含有S33L的抗阿糖胞苷突变体显示对唑菌酯和氨硫霉素的敏感性增加，和一个含有D228N的突变体显示出对环磷酰胺的敏感性增加。体外酶活性试验表明，氨酰苦素不能抑制S33L和D228N点突变的细胞色素bc1复合物的活性。根据S33L的变化设计AS-PCR引物，以检测抗氨黄碱的菌株。
结论：这些结果表明，在实验室中，李氏疫霉对氨精苷具有中等至高的抗性风险。两个变化，S33L和D228N,在PlCytb中可能与观察到的阿糖胞苷耐药性有关。©2022化学工业学会。
