Phytopathology. 2002 Jun;92(6):671-5. doi: 10.1094/PHYTO.2002.92.6.671.
ABSTRACT A fundamental principle of integrated pest management is that actions taken to manage disease should be commensurate with the risk of infection and loss. One of the less-studied factors that determines this risk is ontogenic, or age-related resistance of the host. Ontogenic resistance may operate at the whole plant level or in specific organs or tissues. Until recently, grape berries were thought to remain susceptible to powdery mildew (Uncinula necator) until late in their development. However, the development of ontogenic resistance is actually quite rapid in berries, and fruit become nearly immune to infection within 4 weeks after fruit set. Our objective was to determine how and at what stage the pathogen was halted in the infection process on ontogenically resistant berries. Adhesion of conidia, germination, and appressorium formation were not impeded on older berries. However, once berries were approximately 3 weeks old and older, few germlings were able to form secondary hyphae. Ontogenically resistant berries responded rapidly to infection by synthesis of a germin-like protein that had been previously shown to play a role in host defense against barley powdery mildew. On susceptible berries, cell discoloration around penetration sites indicated the oxidation of phenolic compounds; a process that was followed by localized cell death. However, the pathogen was still able to infect such cells prior to their death, continue secondary growth, and thereby colonize young berries. Formation of papillae was not involved in the differential resistance mechanism of older berries. In susceptible berries, papillae formed frequently at infection sites but did not always contain the pathogen, whereas in resistant berries, the pathogen was always halted prior to the formation of papillae. The host defense, which conditions ontogenic resistance, operates in the earliest stages of the infection process, in the absence of gross anatomical barriers, prior to the formation of a functional haustorium and prior to the development of a conspicuous penetration pore. We also found that diffuse powdery mildew colonies that were not visible in the field predisposed berries to bunch rot by Botrytis cinerea, increased the levels of infestation by spoilage microorganisms, and substantially degraded wine quality. Our improved understanding of the nature, causes, and stability of ontogenic resistance in the grapevine/ powdery mildew system has supported substantial changes in how fungicides are used to control the disease. Present applications are more focused on the period of maximum fruit susceptibility instead of following a calendar-based schedule. This has improved control, reduced losses, and in many cases reduced the number of fungicide applications required to suppress the disease. Particularly where fungicides are deployed in a programmatic fashion and ontogenic resistance is dynamic, there may be equivalent improvements to be made in other hostpathogen systems through studies of how host susceptibility changes through time.
综合虫害管理的一个基本原则是，管理疾病的措施应与感染和损失的风险相称。决定这种风险的一个研究较少的因素是宿主的个体发育或与年龄相关的抗性。个体发育抗性可能在整个植物水平或特定器官或组织中起作用。直到最近，人们还认为葡萄浆果在其发育后期仍易受白粉病（Uncinula necator）的感染。然而，浆果中的个体发育抗性实际上发展得非常快，果实套袋后 4 周内几乎对感染具有免疫力。我们的目标是确定病原体在个体发育抗性浆果的感染过程中是如何以及在哪个阶段被阻止的。在较老的浆果上，孢子的附着、萌发和附着胞的形成并没有受到阻碍。然而，一旦浆果大约 3 周龄或更老，很少有芽管能够形成次生菌丝。个体发育抗性浆果通过合成一种先前被证明在大麦白粉病中对宿主防御起作用的芽管蛋白迅速对感染作出反应。在易感浆果上，穿透部位周围细胞的变色表明酚类化合物的氧化；这一过程随后导致局部细胞死亡。然而，病原体仍然能够在这些细胞死亡之前感染它们，继续进行二次生长，并因此定植于幼果。在老浆果的差异抗性机制中不涉及乳突的形成。在易感浆果上，乳突经常在感染部位形成，但并不总是包含病原体，而在抗性浆果上，病原体总是在乳突形成之前被阻止。在没有明显的解剖学障碍的情况下，在形成功能性吸器和明显的穿透孔之前，在感染过程的最早阶段，即在宿主防御作用下，条件产生了个体发育抗性。我们还发现，在田间不易察觉的弥漫性白粉病菌落使浆果易受葡萄孢菌引起的果穗腐烂的影响，增加了腐烂微生物的侵染水平，并大大降低了葡萄酒的质量。我们对葡萄/白粉病系统中个体发育抗性的性质、原因和稳定性的认识的提高，支持了如何使用杀菌剂来控制该疾病的重大变化。目前的应用更加集中在果实最易受感染的时期，而不是按照日历安排。这提高了控制效果，减少了损失，在许多情况下减少了抑制疾病所需的杀菌剂施用量。特别是在杀菌剂以计划的方式部署并且个体发育抗性具有动态性的情况下，通过研究宿主易感性随时间的变化，在其他宿主-病原体系统中可能会有同等程度的改进。
