Screening for costs of disease resistance caused by stomatal dysfunction

事实证明，结合高产和对英国三种主要叶部病害(黑斑病、黄锈病和褐锈病)具有良好抗性的小麦品种是难以捉摸的。现在，科学文献中有重要的证据表明，一些通过传统植物育种引入品种的抗病基因会对作物造成产量损失。因此，抗病育种会造成“产量拖累”，从而减缓产量提高的速度。这抑制了育种者将精力集中在抗性选择上，因此大多数商业上受欢迎的高产小麦品种都容易受到叶部疾病的影响。其结果是，杀菌剂被常规用于控制重要的叶部疾病。对杀菌剂的依赖与种植者的高投入成本和致病病原体对所使用的杀菌剂不敏感的强大压力有关，从而减少了仍然有效的杀菌剂的数量。这里提出的项目将测试重要的抗病基因对可获得产量的影响。目前在植物育种计划中很难做到这一点，因为：(I)有大量的基因需要测试，(Ii)在没有仔细的实验的情况下，每个基因造成的产量损失的测量被它们通过疾病控制提供的产量好处所掩盖，(Iii)测试需要产生在存在或不存在抗病基因方面存在差异但在其他方面高度相似的小麦品系。为了排除抗病和感病小麦品系之间的其他差异对产量造成的影响，这一点很重要。如果能够在不产生产量成本的情况下，选择能够提供疾病控制益处的抗病基因将是有用的。最近，越来越多的证据表明，对产量的有害影响可能是由于叶表面细胞的抗病反应扰乱了相邻气孔的功能。气孔是叶片表面的气孔，通常在白天打开(允许二氧化碳进入叶片进行光合作用)，晚上关闭(以防止叶片不进行光合作用时不必要的水分损失)。由于抗性反应引起的气孔功能障碍，它们可能在白天不能完全打开，或者在晚上不能正常关闭。这里提出的项目将检验这样一种想法，即气孔功能的测量可以用于筛选抗性基因，以确定哪些基因可能对产量产生有害影响，哪些可能不会对产量产生有害影响。这将允许小麦育种者专注于导入基因，这些基因对叶片疾病有效，对植物的影响也是良性的。

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.