Accelerated breeding of black rot resistant brassicas for the benefit of east African smallholders

植物抗病基因可以保护作物免受含有相应无毒基因(AVR)的病原菌的侵染。在许多情况下，单一的、通常是显性的抗病(R)基因提供的保护是短暂的，因为病原体菌株可以通过突变和选择进化，有利于具有改变或缺失AVR基因的菌株，因此能够导致疾病。广谱抗病是定量的，涉及几个基因，通常预计会更持久。然而，这种抗性在育种计划中更难利用。这种植物防御策略的基础目前尚不清楚。我们选择甘蓝型油菜对野油菜黄单胞菌(Xanthomonas campestris PV campestris，Xcc)的数量抗性作为研究模型。Xcc引起十字花科植物黑腐病。这种由种子传播的病害是世界范围内最重要的甘蓝病害之一。在WHRI之前的油菜研究中，我们已经确定了良好的抗性来源，并绘制了主要遗传成分的位置。在这个项目中，我们将利用油菜基因组学中令人兴奋的新发展，以及关于油菜和拟南芥基因组之间密切联系的新信息来描述抗性并鉴定相关基因。在拟议的项目中结合上述资源将使我们能够在作物物种数量抗病的基本基础上提供新的和令人兴奋的信息。这项工作的主要实际成果将是获得具有紧密连锁分子标记的抗病植物材料，以及有关油菜基因组中抗性自然变异程度的信息，这些信息可用于植物育种，以提供对一种非常重要的病原菌的持久抗性。

Plant disease resistance genes can protect crops against pathogens that have the corresponding avirulence (avr) genes. In many cases, the protection conferred by single, generally dominant, disease resistance (R) genes is short lived as the pathogen strains can evolve through mutation and selection, favouring strains with altered or missing avr genes that are therefore able to cause disease. Broad spectrum disease resistance that is quantitative, involving several genes, is generally expected to be more durable. However, this kind of resistance is more difficult to exploit in breeding programmes. The basis of this plant defence strategy is currently unknown. We have chosen quantitative resistance to Xanthomonas campestris pv campestris (Xcc) in Brassica rapa as a model for investigation. Xcc causes black rot of crucifers. This seed-borne disease is one of the most important diseases of Brassicas worldwide. In previous Brassica research at WHRI we have identified good sources of resistance and mapped the location of the major genetic components. In this project we will exploit the exciting new developments in Brassica rapa genomics and emerging information on the close relatedness of the Brassica and Arabidopsis genomes to characterise the resistance and identify the genes involved. The combination of the above resources in the proposed project will allow us to deliver novel and exciting information on the fundamental basis of quantitative disease resistance in a crop species. Key practical outcomes of this work will be resistant plant material with tightly linked molecular markers and information on the extent of natural variation for resistance in Brassica genomes that could be exploited in plant breeding to provide durable resistance to a very significant pathogen.