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

细菌性溃疡病是全球樱桃的主要病害。这种多年生树木疾病非常复杂，由几种不同的假单胞菌病原体引起，它们在整个季节占据不同的组织。尽管育种可以在限制这种疾病方面发挥关键作用，但对细菌溃疡病抗性的遗传学几乎一无所知。过去和正在进行的研究表明，Merton Glory和Colney等樱桃品种对所有病原体都具有广泛的抗性。预计这种抗性是定量的，可能涉及一系列在组织类型之间表现出差异表达的性状。该博士将通过对在East Malling繁殖的野生和物种水平的樱桃种群进行基因分型和表型分型，重点描述抗性的遗传基础，目的是确定与溃疡病抗性相关的新型抗性来源。这将导致广泛抗性标记的发展，这将在育种计划中非常有用，并且已经应用于其他主要疾病，如苹果的火枯病。此外，学生将开始研究不同宿主组织中耐药反应的生物学基础，并优化表型筛选试验。不同组织类型在宿主抗性中的相对重要性尚不清楚，对主要疾病发生的木质组织中发生的免疫反应知之甚少。正在进行的细菌性溃疡病研究表明，不同的组织对不同分支的假单胞菌的易感性各不相同。田间观察到的抗性在实验室的叶片和果实分析中不能完全复制。这突出了理解抗性潜在机制的重要性，特别是在木本组织中。学生将优化分析以了解免疫反应，例如测量活性氧和研究免疫基因表达。他们将使用荧光标记菌株的显微镜来跟踪抗性和易感植物的感染，并描述宿主反应的关键差异。本博士所开发的工具将有助于快速准确的抗性筛选，并提高我们对果树病原体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.