Screening for costs of disease resistance caused by stomatal dysfunction

在英国，结合高产和对三种主要叶部疾病（壳针孢斑点病、黄锈病和褐锈病）的良好抗性的小麦品种已被证明是难以捉摸的。现在科学文献中有重要证据表明，通过常规植物育种引入品种的一些抗病基因对作物的产量造成了惩罚。因此，抗病育种造成了“产量拖累”，减缓了产量提高的速度。这抑制了育种者集中精力进行抗性选择，因此大多数商业上流行的高产小麦品种易受叶面病害的影响。其结果是，杀真菌剂通常用于控制重要的叶面病害。对杀真菌剂的依赖与种植者的高投入成本和致病病原体对所用杀真菌剂不敏感的强大压力有关，从而减少了保持有效的杀真菌剂的数量。这里提出的项目将测试重要的抗病基因对可达到的产量的影响。这在目前的植物育种计划中难以实现，因为：（i）有大量的基因要测试，（ii）在没有仔细实验的情况下，对由每个基因引起的产量损失的测量被它们通过疾病控制提供的产量益处所隐藏，以及（iii）测试需要产生因抗性基因的存在或不存在而不同但在其他方面高度相似的小麦品系。这一点很重要，以便排除由抗性和敏感小麦品系之间的其他差异引起的对产量的任何影响。能够选择提供疾病控制益处而没有相关产量成本的抗性基因将是有用的。最近，越来越多的证据表明，对产量的有害影响可能是由叶表面细胞的抗病反应破坏相邻气孔的功能引起的。气孔是叶片表面的气孔，通常在白天打开（允许CO2进入叶片进行光合作用），在晚上关闭（防止叶片不进行光合作用时不必要的水分流失）。由于气孔功能障碍所造成的阻力反应，他们可能无法完全开放，在白天或夜间无法关闭。本文提出的项目将测试气孔功能的测量可以用于筛选抗性基因的想法，以确定那些可能对产量产生有害影响的基因。这将使小麦育种者能够集中精力引入对叶面疾病有效且对植物无害的基因。

Wheat varieties combining high yield and good resistance against three of the main foliar diseases in the UK (Septoria tritici blotch, yellow rust and brown rust) have proved elusive. There is now significant evidence in the scientific literature that some disease resistance genes, introduced into varieties by conventional plant breeding, impose a yield penalty on the crop. Hence, breeding for disease resistance creates 'yield drag' which slows the rate of yield improvement. This acts as a disincentive for breeders to focus efforts on selection for resistance, so most commercially popular, high yielding wheat varieties are susceptible to foliar diseases. The result of this is that fungicides are routinely used to control important foliar diseases. Dependence on fungicides is associated with high input costs for the grower and strong pressure for the disease-causing pathogens to develop insensitivity to the fungicides used, reducing the number of fungicides that remain effective. The project proposed here will test important disease resistance genes for their effects on attainable yield. This is difficult to achieve in plant breeding programmes currently, because: (i) there are large numbers of genes to test, (ii) without careful experimentation, measurements of the yield loss caused by each gene are hidden by the yield benefit they provide via disease control, and (iii) testing requires production of wheat lines that differ for presence or absence of the resistance gene but are otherwise highly similar. This is important in order to rule out any effects on yield caused by other differences between the resistant and susceptible wheat lines. It would be useful to be able to select resistance genes which provide the benefit of disease control, without an associated yield cost. Recently, evidence has accumulated that the deleterious effects on yield may be caused by disease resistance responses in the cells of the leaf surface disrupting the function of adjacent stomata. Stomata are pores in the leaf surface that normally open during the day (to allow CO2 to enter the leaf for photosynthesis) and close at night (to prevent unnecessary water loss when the leaf is not photosynthesising). As a result of the stomatal dysfunction caused by the resistance response, they may fail to open fully during the day or fail to shut properly at night. The project proposed here will test the idea that measurements of stomatal function can be used to screen resistance genes, to identify those which are, or are not, likely to have deleterious effects on yield. This would allow wheat breeders to focus on introducing genes which are effective against foliar diseases and benign in their effects on the plant.