Koike S T
University of California Cooperative Extension, Salinas 93901.
Plant Dis. 1998 Sep;82(9):1063. doi: 10.1094/PDIS.1998.82.9.1063B.
Over the past 5 years, commercial acreage of the leafy crucifer arugula (Eruca sativa) has increased greatly in the Salinas Valley (Monterey County), California, and the crop is an important component in packaged salad products. A foliar disease has affected this crop and at times reduced its quality to the extent that it could not be harvested. Symptoms consisted of small (1 to 4 mm in diameter), irregular, dark brown to black speckling on adaxial leaf surfaces. Speckling sometimes expanded into tan spots 3 to 8 mm in diameter. Corresponding abaxial surfaces usually supported white fungal growth typical of a downy mildew. Conidiophores had main trunks with dichotomous branches ending in slender curved tips. Conidia were ovoid in shape, measuring 22 to 25 μm long and 19 μm wide. The fungus was identified as Peronospora parasitica. Pathogenicity was established by gently pressing diseased leaves onto arugula test plants and incubating plants in a humidity chamber for 48 h. Downy mildew developed after 6 days and the same fungus was observed. Although this disease has occurred on this crop for several years, this is the first documentation of P. parasitica on arugula in California. A previously described foliar bacterial disease caused by Pseudomonas syringae (1) has similar symptoms, making field diagnoses difficult if fungal signs of the downy mildew are not present on the leaf. Reference: (1) S. T. Koike et al. Plant Dis. 80:464. 1996.
在过去5年里，叶用十字花科植物芝麻菜（Eruca sativa）在加利福尼亚州萨利纳斯山谷（蒙特雷县）的商业种植面积大幅增加，并且该作物是包装沙拉产品中的一个重要组成部分。一种叶部病害影响了这种作物，有时会降低其品质，以至于无法收获。症状表现为叶片正面出现小的（直径1至4毫米）、不规则的、深褐色至黑色的斑点。斑点有时会扩大成直径3至8毫米的黄褐色病斑。相应的叶片背面通常有霜霉病特有的白色真菌生长。分生孢子梗有主干，具二叉状分枝，末端为细长的弯曲尖端。分生孢子呈卵形，长22至25微米，宽19微米。该真菌被鉴定为寄生霜霉。通过将病叶轻轻压在芝麻菜试验植株上，并将植株在湿度箱中培养48小时来确定致病性。6天后出现霜霉病，且观察到相同的真菌。尽管这种病害在这种作物上已发生数年，但这是加利福尼亚州首次有寄生霜霉在芝麻菜上的记录。一种先前描述的由丁香假单胞菌引起的叶部细菌病害（1）有相似症状，如果叶片上没有霜霉病的真菌迹象，会使田间诊断变得困难。参考文献：（1）S. T. Koike等人，《植物病害》80:464，1996年。
