油菜病害:黑腿病

The fungus Leptosphaeria maculans is the primary cause of blackleg of canola. 另一个物种，L. biglobosa, 会对作物造成轻微损害，但不会对北达科他州的油菜籽造成严重威胁.

L. maculans is genetically variable, 不同的种(以前在油菜中称为致病群)随着病原菌战胜抗性基因而发展. 种的流行率随着杂交品种中抗性基因的变化而变化. When a resistant hybrid is planted continuously, 尤其是在短时间的旋转中, 比赛s capable of attacking it will increase in prevalence.

If this selection pressure is not managed properly, 由于黑腿造成的产量损失将增加到杂交品种中存在的抗性基因不再有用的程度. 因此, 种植具有适当抗性来源的品种对黑腿病的治理至关重要.

以前, 感染携带抗性基因Rlm1或Rlm2的品种的小种被归为致病性组2 (PG-2)。, and 比赛s that attack cultivars carrying resistance genes Rlm1, Rlm2 or Rlm3 were grouped within PG-4. While multiple 比赛s can be contained in each PG, they all have the ability to infect cultivars that carry the resistance genes listed.

图片来源:

Luis del Rio Mendoza, NDSU

图1. 子叶上的病变

在子叶、叶、茎和豆荚上可观察到该病的体征和症状(图1-4)。. 子叶(图1)和叶片(图2a和B)的病变形状为圆形到不规则，浅棕色到棕褐色. 病灶表面可见小的深色真菌假孢子(这些结构释放无性孢子称为假孢子).

图片来源:

山姆·马克尔，NDSU

图2. A–Foliar lesion with profuse pycnidia

图片来源:

Luis del Rio Mendoza, NDSU

图2. B-Foliar病变

在感染, 真菌通过维管系统进入主茎，向冠和根区域移动. Stem lesions may result in rotting and canker development in the crown area or where the stem is attached to the leaves; however, lesions may form on any part of the stem. 在极端的疾病压力下，茎可能会断裂(图3)并与根系分离(图4)。.

图片来源:

山姆·马克尔，NDSU

图3. 破裂的茎具假体.

The pathogen can infect canola plants at any stage of development. 然而, 发生在幼苗期和第四至第六叶生长期之间的感染到达树冠的机会最高，通常会造成重大的经济损失.

图片来源:

山姆·马克尔，NDSU

图4. 茎具环状病变

在季节后期受到影响的植物表现出类似营养缺乏和水分胁迫的症状. 这些植物在茎上可能没有明显的病变或溃烂，但在基茎内部可能有深色变色.

Root discoloration and rotting can cause premature death and yield reduction. Infected pods may result in seed infection, and they might shed and result in yield loss.

The pathogen overwinters on canola residue as pseudothecia, which are small dark-colored 性ual fruiting bodies. 在春天, ascospores are produced and disseminated by the wind over long distances; however, most remain close to the source.

While ascospores can be released after one year of overwintering, ascospore release reaches its maximum rate on 2-year-old stubble. 一旦病变形成，弧菌将发展并产生无性孢子作为次级接种物. 这些孢子可以通过风和雨的飞溅传播很短的距离，并在田地里造成“热点”.

The pathogen also can survive on canola seeds. When seed-borne infections occur, emerged seedlings show the lesions on cotyledons. Infected plants might become stunted and die premature.

The severity of the disease is higher in regions with frequent rainfall, 以及温暖潮湿的环境. 然而, 在干燥的条件下，如果季节早期的阵雨分散了接种物，这种疾病就会有问题.

当空气温度在55 - 70华氏度之间，相对湿度高于80%时，孢子的扩散最大. 风在引起原发性和继发性感染的有性和无性孢子的传播中也起着重要作用, 分别.

Integrated pest management (IPM) strategies such as cultural practices, 认证的种子, 在黑腿病的管理中，强烈建议使用种子处理和杀菌剂.

侦察: 侦察对于确定管理工具(如遗传抗性)是否有效很重要. 子叶和下叶可见黄褐色病变，中心有小的深色胡椒状结构(花椒). Stem cankers and vascular discoloration may be visible as the season progresses.

电阻: Planting resistant cultivars is an essential part of blackleg management. More than a dozen resistance genes have been identified, although not all of them have been incorporated into commercial hybrids. 一些种子公司正在根据它们携带的抗性基因给它们的杂交品种贴上标签. Rotation of resistance genes is important for long-term effective management. 根据经验，避免在两个以上的连续生长季节种植同一种杂交作物.

轮作: Two-year old canola residues produce the highest amounts of ascospores; therefore, avoid planting canola every other year if blackleg is a problem. 另外, 紧密的轮换可以加快病原体产生新菌种和克服抗性基因的速度. A three-year rotation will help manage the disease.

避免油菜籽残留物: When possible, avoid planting canola close to a previous year’s crop residue. 前一季的油菜残茬可以作为新种植的重要接种物来源. 而1,500 feet of separation is ideal, 甚至更短的播种间隔也会减少孢子传播到新作物的数量.

杂草管理: Common weeds such as shepherd’s purse and wild mustard, 还有志愿者的油菜, can be infected by blackleg and will serve as sources of inoculum. 杂草和感染黑腿病的志愿者降低了轮作减少接种量的效果.

认证的种子: 种植无病种子可以防止种子传播感染和将疾病引入新的地区.

种子处理: Seed treatments can protect the seedlings from early infection, especially when the disease pressure is high. 然而, treated seeds provide protection for no longer than three weeks after planting. Multiple compounds have been registered for seed treatment in North Dakota. For the most recent information, see the “North Dakota Field Crop Disease 管理 Guide” (扩展 publication PP622).

杀菌剂乐虎集团程序: In some cases, foliar fungicide application may help manage blackleg. 有几个因素, including resistance level of the hybrid, 轮作计划, weather conditions and inoculum presence, should be taken into consideration before making any fungicide applications. 叶面施用最有效的时间通常是植物处于二到四叶生长期的时候. 正在开发预测子囊孢子阵雨时间对疾病发展的影响的预测模型，并帮助确定最佳的杀菌剂施用时间. 将这些模型纳入预测系统的工作正在进行中，这可能有助于种植者在未来做出管理决策.

Consult the most recent publication of the “North Dakota Field Crop Fungicide Guide” (扩展 publication PP622) for more information regarding foliar applications.

North Dakota State University, Fargo, North Dakota

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