Characterising broad acting resistance to bacterial canker of cherry and elucidating tissue specific mechanisms of immunity

细菌溃烂病是全球樱桃的主要病害之一。这种多年生树木疾病非常复杂，由几种不同的假单胞菌引起，它们在整个季节占据不同的组织。对细菌溃烂的抗性遗传学几乎一无所知，尽管育种在限制这种疾病方面可能发挥关键作用。过去和正在进行的研究表明，默顿、荣耀和科尔尼等樱桃品种对所有病原体都表现出广泛的抗性。据预测，这种抗性是数量上的，可能涉及一系列在组织类型之间表现出差异表达的性状。这一博士学位将侧重于通过对在East Mling繁殖的野生和物种水平的樱桃种群进行基因分型和表型鉴定来表征抗性的遗传基础，目的是识别与溃烂抗性相关的新的抗性来源。这将导致广泛抗性标记的开发，这将在育种计划中非常有用，并已用于其他重大疾病，如苹果火疫病。此外，学生将开始研究不同宿主组织中耐药性反应的生物学基础，并优化表型鉴定的筛选方法。不同组织类型在寄主抗性中的相对重要性尚不清楚，对发生主要疾病的木质组织中发生的免疫反应了解很少。正在进行的关于细菌溃烂的研究表明，不同的组织对不同的假单胞菌分支的敏感性不同。田间观察到的抗性不能在实验室的叶片和果实检测中完全复制。这突出了了解抗性的潜在机制的重要性，特别是在木质组织中。学生将优化分析以了解免疫反应，例如测量活性氧物种和研究免疫基因的表达。他们将使用荧光标记菌株的显微镜来跟踪抗病和感病植物的感染情况，并表征宿主反应的关键差异。本博士论文所提供的工具将有助于开发快速、准确的抗性筛选方法，并提高我们对树木果实病原菌的组织特异性抗性反应的理解。

Bacterial canker is a major disease of cherry globally. This perennial tree disease is highly complex, caused by several distinct Pseudomonas pathogens that occupy different tissues throughout the season. Almost nothing is known about the genetics of resistance to bacterial canker, despite the key role breeding could play in limiting this disease. Past and ongoing research has shown that broad resistance to all pathogens is exhibited by cherry cultivars such as Merton Glory and Colney. This resistance is predicted to be quantitative and likely involves a range of traits that exhibit differential expression between tissue types. This PhD would focus on characterising the genetic basis of resistance by genotyping and phenotyping wild and species-level cherry populations propagated at East Malling, with the aim to identify novel sources of resistance associated with canker resistance. This would lead to the development of markers for broad resistance, which would be highly useful in breeding programs and have already been implemented for other major diseases, such as fireblight in apple. In addition, the student would begin to study the biological basis of resistance responses in different host tissues and optimise screening assays for phenotyping. The relative importance of different tissue types in host resistance is unknown, and very little is understood about the immune responses that occur in woody tissues where the main disease occurs. Ongoing work on bacterial canker has shown that different tissues vary in their susceptibility to the different clades of Pseudomonas. Resistance seen in the field is not replicated fully in leaf and fruit assays in the laboratory. This has highlighted the importance of understanding the underlying mechanisms of resistance, particularly in woody tissues. The student will optimise assays to understand immune responses e.g. measurement of reactive oxygen species and study immune gene expression. They will use microscopy of fluorescently tagged strains to follow infection in resistant and susceptible plants and characterise the key differences in host response. The tools produced in this PhD will aid the development of rapid and accurate resistance screening as well as improve our understanding tissue-specific resistance responses to tree fruit pathogens generally.