Xanthomonas plant diseases: mitigating existing, emerging and future threats to UK agriculture

油菜种植是全球价值数十亿美元的产业，而黄单胞菌是一种细菌性植物病原体，可侵染350多种植物，包括许多油菜。这个多学科项目汇集了微生物学、基因组学、病理学、成像、分子生物学和风险评估方面的专家，利用涉及大规模基因组测序的方法，对植物病原菌野油菜黄单胞菌(Xanthomonas campestris，XC)进行了首批大规模综合研究之一，并利用一套独特的油菜多样性系进行植物成像和病原菌抗性筛选。我们的目标是提高知识，支持在英国和其他面临类似挑战的国家有效繁殖和部署适当的防治策略。我们的中心重点是十字花科植物黑腐病(XC PV)。Campestris或Xcc)，可侵染所有栽培的甘蓝。XCC是一种种子传播的维管束(允许水分和营养物质流动的组织)疾病，可能是世界上最重要的蔬菜甘蓝(如卷心菜、花椰菜、西兰花、球芽甘蓝和甘蓝)的病害。XCC还侵染甘蓝型油菜(瑞典油菜)、芥菜(芥菜)和油菜(萝卜、大白菜)。因此，这真的很重要。Xcc可能导致作物完全损失，尽管在英国，它通常会导致质量和适销性下降。Xcc有两个主要问题。首先，与大多数细菌植物病原体不同，对于真菌病原体，没有简单的化学干预。氯氧铜等传统杀菌剂正在停止销售。其次，这项提议的一个关键驱动因素是，商业甘蓝品种几乎没有抗药性--这可能已经被培育出来了。因此，我们将回到野生亲缘关系中，幸运的是，华威的英国蔬菜种质库保存了6000多份甘蓝种质。显然，这太难处理了，但我们最近(在Defra的资助下)产生了我们所说的Brassica多样性固定基础集(DEF)。这些设计是为了捕捉纯合品系群体中的大部分遗传变异，然后可以对这些品系进行Xcc抗性筛选。这个项目将用于甘蓝、甘蓝型油菜和干扰的C基因组作物的野生亲缘关系。我们还幸运地拥有欧洲最大的Xanthomonas分离物(约1,000个)以及英国最有知识的Xanthomonas病理学家Joana Vincente博士。我们将对这个收集的900多个黄单胞菌分离物进行测序，这样我们就可以解决该领域的一些关键挑战，例如什么是病原体，黄单胞菌病原体需要部署哪些关键基因来在特定植物上致病，以及病原体如何随着时间的推移而变化。这项工作的主要成果将是一大套诊断标记，这些标记可用于识别黄单胞菌的特定病原体，即使在田间也是如此！我们将结合这些研究，使用两种互补的成像方法，即荧光/生物发光记者和植物内源叶绿素荧光，了解病原体如何在植物中感染和繁殖-这种荧光随着疾病的进展而变化。我们还打算提出这样的问题，我们能否利用有益的土壤真菌来预防Xcc疾病，以及害虫(如蚜虫)在取食受感染的植物后是否会在田间传播这种疾病？全球社区真正关注的问题之一是病原体的入侵。因此，除了建议的诊断工作外，我们还将对毁灭性的玉米黄单胞病进行详细的风险评估，该疾病正在美国迅速传播，在一些地区造成超过50%的损失。这项评估还将考虑其他被认为可能“处于危险”的作物所面临的风险。

Brassica cultivation is a multi-billion dollar industry worldwide and Xanthomonas is a bacterial plant pathogen pathogens that can infect more than 350 plant species including many brassicas. This multidisciplinary project brings together experts in microbiology, genomics, pathology, imaging, molecular biology and risk assessment to take one of the first large scale integrated studies of the plant pathogen Xanthomonas campestris (Xc), using approaches involving large scale genomic sequencing, in planta imaging and screening for pathogen resistance using a unique set of brassica diversity lines. The objectives are to enhance knowledge and support effective breeding and deployment of appropriate control strategies for Xanthomonas in the UK and other countries that face similar challenges.Our central focus is on black rot of crucifers (Xc pv. campestris or Xcc for short) which can attack all cultivated brassicas. Xcc, is a seed-borne vascular (the tissue that allows water and nutrients to flow) disease and probably the most important disease of vegetable Brassicas (Brassica oleracea; e.g. cabbage, cauliflower, broccoli, Brussels sprouts and kale) in the world. Xcc also infects B. napus (oilseed rape, swede), B. juncea (mustards) and B. rapa (turnip, Chinese cabbage). It is therefore really important. Xcc can cause complete crop loss, though in the UK it usually leads to reduced quality and marketability. There are two main problems with Xcc. First, as with most bacterial phytopathogens, there is no simple chemical interventions, unlike for fungal pathogens. Traditional bactericides such as copper oxychloride are being withdrawn from sale. Secondly, and one key driver of this proposal, there is virtually no resistance in commercial Brassica oleracea varieties - this has probably been bred out. So we are going back to wild relatives and are fortunate that Warwick's UK Vegetable Germplasm collection maintains more than 6000 brassica accessions. Obviously this is far too much to deal with, but we recently (with Defra funding) generated what we call Brassica diversity fixed foundation sets (DFFs). These are designed to capture the majority of the genetic variation in a population of homozygous lines which can then be screened for resistance to Xcc. This project will use DFFSs for Brassica oleracea, Brassica napus and also interfertile C genome crop wild relatives.We are also fortunate to have the largest collection of Xanthomonas isolates in Europe (~ 1,000) as well as the UKs most knowledgable Xanthomonas pathologists Dr Joana Vincente on board. We will sequence more than 900 Xanthomonas isolates from this collection so we can address some of the key challenges in the field, such as what makes a pathogen, what are the key genes a Xanthomonas pathogen needs to deploy to cause disease on specific plants and how the pathogen changes over time. A major output of this work will be a large set of diagnostic markers that can be used to identify specific pathovars of Xanthomonas, even in the field!We will couple these studies to understanding how the pathogen infects and multiplies in the plant using two complementary imaging approaches, fluorescent/bioluminescent reporters and the plant endogenous chlorophyll fluorescence - which changes as disease progresses. We also aim to ask the questions, can we use a beneficial soil fungus to protect from Xcc disease and can insect pests such as aphids transmit the disease in the field following feeding on infected plants?One of the real concerns in a global community is incursions of pathogens. So aside from the diagnostic work proposed, we will also undertake a detailed risk assessment on a devastating Xanthomonas disease of maize, which is rapidly spreading in the US and causing over 50% of losses in some regions. This assessment will also consider risks to other crops considered potentially "at risk".