ETSI Montes, Forestal y del Medio Natural, Dep. Sistemas y Recursos Naturales, Universidad Politécnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain.
Tree Physiol. 2018 Feb 1;38(2):252-262. doi: 10.1093/treephys/tpx123.
Dutch elm disease (DED) is a vascular disease that has killed over 1 billion elm trees. The pathogen spreads throughout the xylem network triggering vessel blockage, which results in water stress, tissue dehydration and extensive leaf wilting in susceptible genotypes. We investigated the differences between four Ulmus minor Mill. clones of contrasting susceptibility to Ophiostoma novo-ulmi Brasier regarding morphological, anatomical and physiological traits affecting water transport, in order to gain a better understanding of the mechanisms underlying DED susceptibility. We analyzed the differential response to water shortage and increased air vapor pressure deficit (VPD) to investigate whether resistance to water stress might be related to DED tolerance. Sixteen plants per clone, aged 2 years, were grown inside a greenhouse under differential watering. Stomatal conductance was measured under ambient and increased VPD. Growth, bark water content and stem hydraulic and anatomical parameters were measured 22 days after starting differential watering. Vessel lumen area, lumen fraction and hydraulic conductance were highest in susceptible clones. Stomatal conductance was lowest under low VPD and decreased faster under increased VPD in resistant clones. We found a negative relationship between the decrease in stomatal conductance at increased VPD and specific hydraulic conductance, revealing a narrower hydraulic margin for sustaining transpiration in resistant clones. The effect of water shortage was greater on radial stem growth than on leaf area, which could be explained through an extensive use of capacitance water to buffer xylem water potential. Water shortage reduced stomatal conductance and vessel lumen area. Bark water content under conditions of water shortage only decreased in susceptible clones. Higher hydraulic constraints to sap flow in resistant clones may determine higher stomatal sensitivity to VPD and so contribute to DED resistance by limiting pathogen expansion and reducing water loss and metabolic impairment in cells involved in fighting against infection.
荷兰榆树病（DED）是一种血管疾病，已导致超过 10 亿棵榆树死亡。病原体在木质部网络中传播，引发血管阻塞，导致水胁迫、组织脱水和易感基因型的广泛叶片萎蔫。我们研究了四个对 Ophiostoma novo-ulmi Brasier 具有不同易感性的 Ulmus minor Mill. 无性系在影响水分运输的形态、解剖和生理特征方面的差异，以更好地了解 DED 易感性的机制。我们分析了对水分短缺和空气蒸气压亏缺（VPD）增加的差异响应，以研究对水分胁迫的抗性是否与 DED 耐受性有关。每个无性系 16 株，年龄为 2 年，在温室中进行不同的浇水处理。在环境和增加的 VPD 下测量气孔导度。在开始不同浇水后 22 天测量生长、树皮水含量以及茎水力和解剖参数。易感无性系的导管腔面积、腔分数和水力传导率最高。在抗性无性系中，气孔导度在低 VPD 下最低，在增加的 VPD 下下降更快。我们发现增加的 VPD 下气孔导度下降与比水力传导率呈负相关，这表明在抗性无性系中维持蒸腾作用的水力边际更窄。水分短缺对径向茎生长的影响大于对叶面积的影响，这可以通过广泛使用电容水来缓冲木质部水势来解释。水分短缺降低了气孔导度和导管腔面积。只有在易感无性系中，在水分短缺条件下树皮水含量才会降低。在抗性无性系中，对 sap 流的水力限制更高可能会导致气孔对 VPD 的敏感性更高，从而通过限制病原体的扩展以及减少与感染作斗争的细胞中的水分损失和代谢损伤来有助于 DED 抗性。
