Ascochyta blight disease, caused by the necrotrophic fungus Ascochyta rabiei, is a major biotic constraint to chickpea production in Australia and worldwide. Detailed knowledge of the structure of the pathogen population and its potential to adapt to our farming practices is key to informing optimal management of the disease. This includes understanding the molecular diversity among isolates and the frequency and distribution of the isolates that have adapted to overcome host resistance across agroecologically distinct regions. Thanks to continuous monitoring efforts over the past 6 years, a comprehensive collection of A. rabiei isolates was collated from the major Australian chickpea production regions. To determine the molecular structure of the entire population, representative isolates from each collection year and growing region have been genetically characterized using a DArTseq genotyping-by-sequencing approach. The genotyped isolates were further phenotyped to determine their pathogenicity levels against a differential set of chickpea cultivars and genotype-phenotype associations were inferred. Overall, the Australian A. rabiei population displayed a far lower genetic diversity (average Nei’s gene diversity of 0.047) than detected in other populations worldwide. This may be explained by the presence of a single mating-type in Australia, MAT1-2, limiting its reproduction to a clonal mode. Despite the low detected molecular diversity, clonal selection appears to have given rise to a subset of adapted isolates that are highly pathogenic on commonly employed resistance sources, and that are occurring at an increasing frequency. Among these, a cluster of genetically similar isolates was identified, with a higher proportion of highly aggressive isolates than in the general population. The discovery of distinct genetic clusters associated with high and low isolate pathogenicity forms the foundation for the development of a molecular pathotyping tool for the Australian A. rabiei population. Application of such a tool, along with continuous monitoring of the genetic structure of the population will provide crucial information for the screening of breeding material and integrated disease management packages.

中文翻译：

---

澳大利亚Ascochyta rabiei当前的种群结构和致病性模式

壳囊菌枯萎病由坏死性真菌Ascochyta rabiei引起，是澳大利亚和全世界鹰嘴豆生产的主要生物限制因素。详细了解病原体种群的结构及其适应我们农业实践的潜力是为疾病进行最佳管理的关键。这包括了解分离株之间的分子多样性以及已适应克服农业生态不同区域的宿主抗性的分离株的频率和分布。通过过去 6 年的持续监测工作，从澳大利亚主要鹰嘴豆产区收集了全面的狂犬病菌株。为了确定整个种群的分子结构，使用 DArTseq 测序方法对来自每个收集年份和生长区域的代表性分离株进行了遗传表征。对基因分型的分离株进行进一步的表型分析，以确定其对一组差异鹰嘴豆品种的致病性水平，并推断出基因型-表型关联。总体而言，澳大利亚狂犬病种群表现出的遗传多样性（平均 Nei 基因多样性为 0.047）远低于全球其他种群。这可能是由于澳大利亚存在单一交配型 MAT1-2，限制了其繁殖方式为克隆模式。尽管检测到的分子多样性较低，但克隆选择似乎已经产生了适应分离株的子集，这些分离株对常用的抗性来源具有高致病性，并且发生频率不断增加。其中，鉴定出一组遗传相似的分离株，其中高侵袭性分离株的比例高于一般人群。与高和低分离株致病性相关的不同遗传簇的发现为开发澳大利亚拉比埃拉氏菌种群分子病理分型工具奠定了基础。这种工具的应用以及对种群遗传结构的持续监测将为筛选育种材料和综合疾病管理包提供重要信息。