Role of ascospores in further spread of QoI-resistant cytochrome b alleles (G143A) in field populations of Mycosphaerella graminicola
Role of ascospores in further spread of QoI-resistant cytochrome b alleles (G143A) in field populations of Mycosphaerella graminicola
复制标题
DOI：
10.1094/phyto-95-0933
复制
发表时间：
2005-08-01
期刊：
影响因子：
3.2
通讯作者：
Lucas, JA
中科院分区：
文献类型：
--
作者：
Fraaije, BA;Cools, HJ;Lucas, JA
自1997年以来，Strobilurin杀菌剂或醌外抑制剂（QoIs）已在英国成功地用于控制Septoria叶斑病。然而，2002年夏季在洛桑首次报道了对qoi耐药的结核分枝杆菌分离株。细胞色素b基因的序列分析显示，所有耐药菌株都携带一个突变，导致密码子143 （G143A）上的甘氨酸被丙氨酸取代。利用实时聚合酶链反应（PCR）检测的广泛监测显示，基于qoi的杀菌剂处理可以快速选择田间种群中携带抗性a143 (R)等位基因的分离株。这种选择主要是由大量产生的无性分生孢子在短距离上的多环扩散所驱动的。为了研究有性繁殖的空气传播子囊孢子在R等位基因进一步传播中的作用，建立了一种将孢子捕获与实时PCR检测相结合的方法。该方法使我们既能定量测定空气样品中禾草分枝杆菌子囊孢子的数量，又能估计子囊孢子种群中R等位基因的频率。正如预期的那样，大多数子囊孢子是在小麦作物衰老期间生长季节结束时产生的。然而，在生长第32期第一次施用QoI后，在一个小麦地块取样的空气传播子囊孢子群体中，r等位基因频率立即从35%增加到80%。在第二次qi施用后，处理地块叶片和气溶胶中稻瘟病菌群体的r等位基因频率均超过90%。对稻瘟病菌旗叶群体的空间取样和测试表明，携带R等位基因的子囊孢子可以在作物顶端至85 in的距离内迅速传播。收获后，空气样本中检测到的子囊孢子较少，测量的r等位基因频率受到来自附近麦田的子囊孢子的影响。
Strobilurin fungicides or quinone outside inhibitors (QoIs) have been used successfully to control Septoria leaf blotch in the United Kingdom since 1997. However, QoI-resistant isolates of Mycosphaerella gramoinicola were reported for the first time at Rothamsted during the summer of 2002. Sequence analysis of the cytochrome b gene revealed that all resistant isolates carried a mutation resulting in the replacement of glycine by alanine at codon 143 (G143A). Extensive monitoring using real-time polymerase chain reaction (PCR) testing revealed that fungicide treatments based on QoIs rapidly selected for isolates carrying resistant A 143 (R) alleles within field populations. This selection is driven mainly by polycyclic dispersal of abundantly produced asexual conidia over short distances. In order to investigate the role of sexually produced airborne ascospores in the further spread of R alleles, a method integrating spore trapping with real-time PCR assays was developed. This method enabled us to both quantify the number of M. graminicola ascospores in air samples as well as estimate the frequency of R alleles in ascospore populations. As expected, most ascospores were produced at the end of the growing season during senescence of the wheat crop. However, a rapid increase in R-allele frequency, from 35 to 80%, was measured immediately in airborne ascospore populations sampled in a wheat plot after the first QoI application at growth stage 32. After the second QoI application, most R-allele frequencies measured for M. graminicola populations present in leaves and aerosols sampled from the treated plot exceeded 90%. Spatial sampling and testing of M. graminicola flag leaf populations derived from ascospores in the surrounding crop showed that ascospores carrying R alleles can spread readily within the crop at distances of tip to 85 in. After harvest, fewer ascospores were detected in air samples and the R-allele frequencies measured were influenced by ascospores originating from nearby wheat fields.