Rice blast, caused by the fungus Magnaporthe oryzae, is one of the most destructive diseases of rice worldwide. Management through the deployment of host resistance genes would be facilitated by understanding the dynamics of the pathogen’s population in the field. Here, to investigate the mechanism underlying the breakdown of disease resistance, we conducted a six-year field experiment to monitor the evolution of M. oryzae populations in Qujiang from Guangdong. The new variety of Xin-Yin-Zhan (XYZ) carrying R genes Pi50 and Pib was developed using the susceptible elite variety, Ma-Ba-Yin-Zhan (MBYZ), as the recurrent line. Field trials of disease resistance assessment revealed that the disease indices of XYZ in 2012, 2013, 2016, and 2017 were 0.19, 0.39, 0.70, and 0.90, respectively, indicating that XYZ displayed a very rapid increase of disease severity in the field. To investigate the mechanism underlying the quick erosion of resistance of XYZ, we collected isolates from both XYZ and MBYZ for pathogenicity testing against six different isogenic lines. The isolates collected from XYZ showed a similar virulence spectrum across four different years whereas those from MBYZ showed increasing virulence to the Pi50 and Pib isogenic lines from 2012 to 2017. Molecular analysis of AvrPib in the isolates from MBYZ identified four different AvrPib haplotypes, i.e., AvrPib-AP1-1, AvrPib-AP1-2, avrPib-AP2, and avrPib-AP3, verified by sequencing. AvrPib-AP1-1 and AvrPib-AP1-2 are avirulent to Pib whereas avrPib-AP2 and avrPib-AP3 are virulent. Insertions of a Pot3 and an Mg-SINE were identified in avrPib-AP2 and avrPib-AP3, respectively. Two major lineages based on rep-PCR analysis were further deduced in the field population, implying that the field population is composed of genetically related isolates. Our data suggest that clonal propagation and quick dominance of virulent isolates against the previously resistant variety could be the major genetic events contributing to the loss of varietal resistance against rice blast in the field.

由稻瘟病菌引起的稻瘟病是全世界稻米中最具破坏性的疾病之一。通过了解宿主中病原体种群的动态，将有助于通过宿主抗性基因的部署进行管理。在这里，为了调查抗病性崩溃的潜在机制，我们进行了为期六年的田间试验，以监测广东曲江米曲霉种群的演变。携带R基因Pi50和Pib的新品种Xin-Yin- Yan（XYZ）是使用易感精英品种马八贤詹（MBYZ）作为复发系而开发的。疾病抵抗力评估的现场试验显示，XYZ在2012年，2013年，2016年和2017年的疾病指数分别为0.19、0.39、0.70和0.90，这表明XYZ在该领域显示出非常严重的疾病严重度增加。为了研究XYZ抗性快速侵蚀的潜在机制，我们收集了XYZ和MBYZ的分离株，以针对六种不同的等基因系进行致病性测试。从XYZ收集的菌株表现在四个不同的几年类似的毒力谱，而那些来自MBYZ呈递增的毒力的Pi50和的Pib基因系从2012年到2017年的分子分析AvrPib来自MBYZ的分离物中的AmpA鉴定出了四种不同的AvrPib单倍型，即AvrPib-AP1-1，AvrPib-AP1-2，avrPib-AP2和avrPib-AP3，已通过测序验证。AvrPib-AP1-1和AvrPib-AP1-2对Pib无毒，而avrPib-AP2和avrPib-AP3具有毒性。在avrPib-AP2和avrPib-AP3中鉴定出Pot3和Mg-SINE的插入， 分别。在田间种群中进一步推导了基于rep-PCR分析的两个主要谱系，这表明田间种群由遗传相关的分离株组成。我们的数据表明，强毒分离株针对先前抗性品种的克隆繁殖和快速优势可能是造成该领域对稻瘟病的品种抗性丧失的主要遗传事件。