Nelson B D, Mallik I, McEwen D, Christianson T
Department of Plant Pathology, North Dakota State University, Fargo, ND 58102.
Plant Dis. 2008 Jul;92(7):1062-1066. doi: 10.1094/PDIS-92-7-1062.
Phytophthora root rot, caused by Phytophthora sojae, is the most important disease of soybean (Glycine max) in North Dakota. Because of the expansion of soybean hectares and appearance of disease on cultivars with resistance genes, we investigated the pathotypes, distribution, and metalaxyl sensitivity of P. sojae in North Dakota. Soil from 347 soybean fields in 20 counties in eastern North Dakota was collected between 2002 and 2004, and P. sojae was baited from the soil with the susceptible cultivar McCall. The virulence phenotype of each isolate was determined on eight differentials, and all isolates were tested for sensitivity to metalaxyl incorporated into V8 agar. The pathogen was recovered from 80 fields located in five counties. Sixteen pathotypes, which included 14 known races and two previously reported pathotypes that had not been assigned a race, were identified out of 157 isolates. A single pathotype was recovered from 61 fields, 2 pathotypes from 14 fields, 3 pathotypes from 4 fields, and 4 pathotypes from 1 field. Pathotypes with virulence phenotypes 1a,1c,7 (race 4; 39%) and 1a,7 (race 3; 28%) were the most common, representing 67% of the total isolates. One or both of these pathotypes was found in 79% of the fields where P. sojae was recovered. Seven of the 157 isolates showed limited growth on metalaxyl after 14 days of incubation. In the past 10 years, the number of pathotypes of P. sojae in North Dakota has increased from 4 to 16, and pathotypes have developed that can attack the three most common resistance genes found in soybean cultivars for the region.
由大豆疫霉引起的疫霉根腐病是北达科他州大豆（Glycine max）最重要的病害。由于大豆种植面积的扩大以及具有抗性基因的品种上出现病害，我们对北达科他州大豆疫霉的致病型、分布及甲霜灵敏感性进行了调查。在2002年至2004年间，从北达科他州东部20个县的347个大豆田采集土壤，用感病品种麦考尔从土壤中诱捕大豆疫霉。在8个鉴别品种上测定每个分离株的毒力表型，并对所有分离株进行添加到V8琼脂中的甲霜灵敏感性测试。在五个县的80个田块中分离到了该病原菌。在157个分离株中鉴定出16种致病型，其中包括14个已知小种和2个以前报道但未指定小种的致病型。从61个田块中分离到单一致病型，从14个田块中分离到2种致病型，从4个田块中分离到3种致病型，从1个田块中分离到4种致病型。毒力表型为1a、1c、7（小种4；39%）和1a、7（小种3；28%）的致病型最为常见，占分离株总数的67%。在分离到大豆疫霉的田块中，79%的田块发现了这两种致病型中的一种或两种。在157个分离株中，有7个在培养14天后在甲霜灵上生长受限。在过去10年中，北达科他州大豆疫霉的致病型数量从4种增加到16种，并且已经出现了能够攻击该地区大豆品种中发现的三种最常见抗性基因的致病型。
