Understanding resistance to decrease risk of severe phoma stem canker on oilseed rape

利用寄主抗性是防治植物病害最有效、最环保的方法。油菜(Brassica Napus)是英国重要的可耕种作物。由斑点钩端螺旋体引起的茎腐病对该作物的可持续生产构成越来越大的威胁。在英国，尽管使用了杀菌剂，茎腐烂病仍会造成每年1亿英磅的损失。如果欧盟立法不再允许最有效的杀菌剂，这些损失将会增加。此外，据预测，全球变暖将继续增加茎腐烂病流行的范围和严重程度。因此，在不断变化的气候中培育出具有有效抗性的品种以促进国家粮食安全是一项挑战。本项目旨在通过制定有效利用寄主抗性的方案和加深对寄主抗病作用的理解来指导抗病育种，从而降低未来油菜严重茎腐病的风险。甘蓝型油菜对黑斑病的抗性有两种类型，一种是主抗性(R)基因介导的定性抗性，秋季在子叶和叶片中发挥作用；另一种是数量抗性，在初叶侵染后至夏季收获时在叶柄和茎组织中发挥作用。R基因介导的抗性是单基因小种特异性抗性，只有当相应的无毒等位基因在当地斑点落叶松种群中占优势时，才能有效地保护植物。由于斑点落叶松种群的变化，R基因在商业品种上广泛应用后的2到3年内，抗性往往会失效。为了维持R基因抗性的有效性并降低其失效的风险，将对不同地区的斑点落叶松种群进行小种鉴定。利用斑点落叶松小种信息，制定不同R基因品种在空间和时间上的布点方案。Rothamsted先前的工作表明，温度对R基因抗性和数量抗性的有效性都有影响。为了确定在气候变化中油菜对黑斑病的有效抗性，该项目将评估不同类型的抗性在受控环境和自然条件下的有效性。在不同的环境下，对仅含R基因、仅含数量抗性或R基因+数量抗性组合的品种进行检测。从结果中，我们可以评估哪个R基因或哪个抗性组合更有效。这些信息可以用来改进育种策略。为了了解温度如何影响寄主抗性的有效性，本项目将重点研究对温度有不同反应的三个R基因；其中两个基因位于染色体A10上不同位置的同一区域。为了研究R基因的作用机制和对斑点落叶松的数量抗性，将利用具有相同背景的R基因或不同背景的相同R基因的材料。这些材料将使我们能够研究这三个R基因之间的温度响应差异是由于抗性基因还是寄主背景所致。该项目的成果将有助于将油菜严重流行的风险降至最低，从而保持产量，为国家粮食安全做出贡献，并避免不必要的杀菌剂使用。育种人员将从培育具有有效抗病能力的品种的改进策略中受益。通过改进油菜的疾病控制，减少温室气体排放也将使环境受益。

Use of host resistance is the most effective and environmentally friendly way to control plant diseases. Oilseed rape (Brassica napus) is an important arable crop in the UK. The disease phoma stem canker, caused by Leptosphaeria maculans, poses an increasing threat to sustainable production of this crop. In the UK, phoma stem canker cause losses of > £100M p.a., despite use of fungicides. These losses will increase if the most effective fungicides are no longer permitted by EU legislation. Furthermore, it is predicted that global warming will continue to increase the range and severity of phoma stem canker epidemics. There is thus a challenge to produce cultivars with effective resistance in a changing climate to contribute to national food security. This project aims to decrease future risk of severe phoma stem canker on oilseed rape by developing a scheme for effective use of host resistance and by improving understanding of operation of host resistance against the pathogen to guide resistance breeding. The two types of resistance to L. maculans identified in B. napus are major resistance (R) gene mediated qualitative resistance that operates in cotyledons and leaves in autumn and quantitative resistance that operates in leaf stalk and stem tissues, after initial leaf infection until harvest in summer. R gene mediated resistance to L. maculans is single-gene race-specific resistance that is effective in protecting plants only if the corresponding avirulent allele is predominant in the local L. maculans population. R gene resistance often loses its effectiveness in 2 to 3 years after widespread use in commercial cultivars because of changes in L. maculans populations. To maintain the effectiveness of R gene resistance and decrease the risk that it will become ineffective, races in L. maculans populations in different regions will be determined. The L. maculans race information will be used to develop a scheme for deployment of cultivars with different R genes in space and time. Previous work at Rothamsted showed that temperature influences the effectiveness of both R gene resistance and quantitative resistance against L. maculans. To identify effective resistance in oilseed rape that will operate against L. maculans in a changing climate, this project will assess effectiveness of different types of resistance in both in controlled environments and natural conditions. Cultivars with only R genes, only quantitative resistance or combinations of R gene & quantitative resistance will be tested in different environments. From the results, we can assess which R gene or which combination of resistance is more effective. This information can be used to improve breeding strategies. To understand how temperature influences the effectiveness of host resistance, this project will focus on the three R genes which show a differential response to temperature; two of them map in the same region on chromosome A10 at distinct loci. To investigate mechanisms of operation of R gene and quantitative resistance against L. maculans, sets of materials with these R genes in the same background or the same R gene in different backgrounds will be used. These materials will enable us to investigate whether the difference in temperature response between these three R genes is due to the resistance loci or host background. Results from this project will help to minimise the risk of severe epidemics on oilseed rape so that yields are maintained to contribute to national food security and avoid unnecessary fungicide use. Breeders will benefit from improved strategies for breeding cultivars with effective disease resistance. The environment will also benefit from reduced greenhouse gas emissions through improved disease control in oilseed rape.