Phytopathology. 2014 Sep;104(9):908-17. doi: 10.1094/PHYTO-12-13-0333-R.
Verticillium wilt, caused by Verticillium dahliae, is a destructive disease in lettuce, and the pathogen is seedborne. Even though maximum seed infestation rates of <5% have been detected in commercial lettuce seed lots, it is necessary to establish acceptable contamination thresholds to prevent introduction and establishment of the pathogen in lettuce production fields. However, introduction of inoculum into lettuce fields for experimental purposes to determine its long term effects is undesirable. Therefore, we constructed a simulation model to study the spread of Verticillium wilt following pathogen introduction from seed. The model consists of four components: the first for simulating infection of host plants, the second for simulating reproduction of microsclerotia on diseased plants, the third for simulating the survival of microsclerotia, and the fourth for simulating the dispersal of microsclerotia. The simulation results demonstrated that the inoculum density-disease incidence curve parameters and the dispersal gradients affect disease spread in the field. Although a steep dispersal gradient facilitated the establishment of the disease in a new field with a low inoculum density, a long-tail gradient allowed microsclerotia to be dispersed over greater distances, promoting the disease spread in fields with high inoculum density. The simulation results also revealed the importance of avoiding successive lettuce crops in the same field, reducing survival rate of microsclerotia between crops, and the need for breeding resistance against V. dahliae in lettuce cultivars to lower the number of microsclerotia formed on each diseased plant. The simulation results, however, suggested that, even with a low seed infestation rate, the pathogen would eventually become established if susceptible lettuce cultivars were grown consecutively in the same field for many years. A threshold for seed infestation can be established only when two of the three drivers of the disease-(i) low microsclerotia production per diseased plant, (ii) long-tail dispersal gradient, and (iii) low microsclerotia survival between lettuce crops-are present.
黄萎病是由大丽轮枝菌引起的生菜毁灭性病害，病原菌可通过种子传播。尽管在商业生菜种子中检测到最高种子侵染率<5%，但仍有必要建立可接受的污染阈值，以防止病原菌在生菜生产田中引入和建立。然而，为了确定其长期影响而将接种体引入生菜田进行实验是不可取的。因此，我们构建了一个模拟模型来研究病原菌从种子传入后黄萎病的传播。该模型由四个部分组成：第一部分用于模拟宿主植物的感染，第二部分用于模拟病株上微菌核的繁殖，第三部分用于模拟微菌核的存活，第四部分用于模拟微菌核的扩散。模拟结果表明，接种体密度-发病率曲线参数和扩散梯度会影响田间病害的传播。尽管陡峭的扩散梯度有助于在接种体密度较低的新田中建立病害，但长尾梯度可以使微菌核扩散到更远的距离，从而促进高接种体密度田中的病害传播。模拟结果还揭示了避免在同一田地上连续种植生菜、降低作物间微菌核存活率以及在生菜品种中培育对大丽轮枝菌抗性以降低每个病株上形成的微菌核数量的重要性。然而，模拟结果表明，即使种子侵染率很低，如果易感生菜品种在同一田地上连续多年种植，病原菌最终也会定殖。只有当病原菌传播的三个驱动因素中的两个（i）每株病株上微菌核的产量低，（ii）长尾扩散梯度，以及（iii）生菜作物间微菌核的存活率低）存在时，才能建立种子侵染阈值。
