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美国及其他地区仙人掌疫霉对甲霜灵产生抗性的首次报道。

First Report of Resistance to Mefenoxam in Phytophthora cactorum in the United States and Elsewhere.

作者信息

Jeffers S N, Schnabel G, Smith J P

机构信息

Department of Entomology, Soils, and Plant Sciences, Clemson University, Clemson, SC 29634.

Edisto Research and Education Center, Clemson University, Blackville, SC 29817.

出版信息

Plant Dis. 2004 May;88(5):576. doi: 10.1094/PDIS.2004.88.5.576A.

Abstract

Phytophthora cactorum causes crown rot of strawberry (Fragaria × ananassa) (2), a disease that has been particularly severe during the last 5 years in the southeastern United States. In the fall of 2001, strawberry plants (cv. Camarosa) in a field in Lexington County, South Carolina exhibited typical crown rot symptoms (2) 1 to 2 weeks after transplanting, even though plants had been drenched with mefenoxam (Ridomil Gold; Syngenta Crop Protection, Greensboro, NC) immediately after transplanting. Initially, we observed leaves that had marginal necrosis, were smaller than normal, and were discolored. Soon after, diseased plants appeared stunted and unthrifty compared with other plants in the field, and some of these plants eventually wilted and died. Severely affected plants had necrotic roots and decayed crowns. Ten symptomatic plants were collected for isolation. In the laboratory, root and crown tissues were rinsed in running tap water and blotted dry, small pieces of necrotic tissue were placed aseptically on PAR-V8 selective medium (1), and isolation plates were placed at 20°C in the dark for up to 7 days. P. cactorum was recovered from six plants. Isolates produced characteristic asexual and sexual structures directly on the isolation plates (i.e., papillate sporangia on sympodial sporangiophores and oospores with paragynous antheridia) (2). A single hypha of an isolate from each plant was transferred to fresh PAR-V8, and pure cultures were stored on cornmeal agar in glass vials at 15°C in the dark. All six isolates from the Lexington County field and nine other isolates of P. cactorum from strawberry (three from South Carolina, three from North Carolina, and three from Florida) were tested for sensitivity to mefenoxam on fungicide-amended medium. Mefenoxam was added to 10% clarified V8 juice agar (cV8A) after autoclaving so the concentration in the medium was 100 ppm. Agar plugs from active colonies were transferred to mefenoxam-amended and nonamended cV8A (three replicates per treatment), plates were placed at 25°C in the dark for 3 days, and linear mycelium growth was measured. All six isolates from Lexington County were highly resistant to mefenoxam with mycelium growth relatively unrestricted on mefenoxam-amended medium (73 to 89% of that on nonamended medium). In comparison, the other nine isolates were sensitive to mefenoxam with mycelium growth severely restricted by 100 ppm of mefenoxam (0 to 7% of that on nonamended medium). To our knowledge, this is the first report of mefenoxam resistance in P. cactorum on strawberry or any other crop in the United States and elsewhere. Because mefenoxam is the primary fungicide used to manage Phytophthora crown rot in the southeastern United States, resistance may limit use of this fungicide in strawberry production. References: (1) A. J. Ferguson and S. N. Jeffers. Plant Dis. 83:1129, 1999. (2) E. Seemüller. Crown rot. Pages 50-51 in: Compendium of Strawberry Diseases, 2nd ed. J. L. Maas, ed. The American Phytopathological Society, St. Paul, MN, 1998.

摘要

恶疫霉可引发草莓(凤梨草莓)根腐病(2),在美国东南部,这种病害在过去5年尤为严重。2001年秋,南卡罗来纳州列克星敦县一块田地中的草莓植株(品种为卡玛罗莎)在移栽后1至2周出现了典型的根腐病症状(2),即便这些植株在移栽后立即用甲霜灵(瑞毒霉;先正达作物保护公司,北卡罗来纳州格林斯伯勒)进行了灌根处理。最初,我们观察到叶片边缘坏死、比正常叶片小且变色。不久后,患病植株与田间其他植株相比显得矮小且生长不良,其中一些植株最终枯萎死亡。受严重影响的植株根系坏死,根茎腐烂。采集了10株有症状的植株用于分离培养。在实验室中,将根和根茎组织用流动的自来水冲洗并吸干,把小块坏死组织无菌放置在PAR - V8选择性培养基上(1),分离培养平板置于20°C黑暗环境中培养长达7天。从6株植株中分离出了恶疫霉。分离株在分离平板上直接产生了典型的无性和有性结构(即,在合轴式孢子梗上具乳突的孢子囊以及具侧生雄器的卵孢子)(2)。将每株植株分离株的单根菌丝转移至新鲜的PAR - V8培养基上,纯培养物保存在装有玉米粉琼脂的玻璃小瓶中,于15°C黑暗环境下保存。对来自列克星敦县田地的所有6个分离株以及其他9个来自草莓的恶疫霉分离株(3个来自南卡罗来纳州,3个来自北卡罗来纳州,3个来自佛罗里达州)进行了在添加杀菌剂的培养基上对甲霜灵敏感性的测试。在高压灭菌后将甲霜灵添加到10%澄清V8汁琼脂(cV8A)中,使培养基中甲霜灵浓度为100 ppm。将活跃菌落的琼脂小块转移至添加和未添加甲霜灵的cV8A培养基上(每个处理3个重复),平板置于25°C黑暗环境中培养3天,测量线性菌丝生长情况。来自列克星敦县的所有6个分离株对甲霜灵高度抗性,在添加甲霜灵的培养基上菌丝生长相对不受限制(为未添加培养基上生长量的73%至89%)。相比之下,其他9个分离株对甲霜灵敏感,100 ppm甲霜灵严重抑制其菌丝生长(为未添加培养基上生长量的0%至7%)。据我们所知,这是美国及其他地区关于草莓或任何其他作物上恶疫霉对甲霜灵产生抗性的首次报道。由于甲霜灵是美国东南部用于防治疫霉根腐病的主要杀菌剂,抗性可能会限制该杀菌剂在草莓生产中的使用。参考文献:(1)A. J. 弗格森和S. N. 杰弗斯。《植物病害》83:1129,1999。(2)E. 泽米勒。根腐病。载于:《草莓病害简编》第2版,J. L. 马斯主编。美国植物病理学会,明尼苏达州圣保罗,1998,第50 - 51页。

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