Hanson L E
USDA-ARS, Sugar Beet and Bean Research Unit, 494 PSSB, Michigan State University, East Lansing 48824-1325.
Plant Dis. 2010 May;94(5):504-509. doi: 10.1094/PDIS-94-5-0504.
In recent years, growers in Michigan and other sugar beet (Beta vulgaris) production areas of the United States have reported increasing incidence of root rot with little or no crown or foliar symptoms in sugar beet with Rhizoctonia crown and root rot. In addition, Rhizoctonia-resistant beets have been reported with higher levels of disease than expected. In examining beets with Rhizoctonia root rot in Michigan, over 50% of sampled roots had a second potential root rot pathogen, Rhizopus stolonifer. Growing conditions generally were not conducive to disease production by this pathogen alone, so we investigated the potential for interaction between these two pathogens. In greenhouse tests, four of five sugar beet varieties had more severe root rot symptoms when inoculated with both pathogens than when inoculated with either pathogen alone. This synergism occurred under conditions that were not conducive to disease production by R. stolonifer. Host resistance to Rhizoctonia crown and root rot reduced diseases severity, but was insufficient to control the disease when both pathogens were present. This raises concerns about correct disease diagnosis and management practices and indicates that a root rot complex may be important on sugar beet in Michigan.
近年来，美国密歇根州及其他甜菜（Beta vulgaris）产区的种植者报告称，患有丝核菌冠腐和根腐病的甜菜出现根腐病的发病率不断上升，而冠部或叶片症状很少或没有。此外，据报道，抗丝核菌的甜菜病害水平高于预期。在检查密歇根州患有丝核菌根腐病的甜菜时，超过50%的采样根有第二种潜在的根腐病病原体——匍枝根霉。一般来说，生长条件并不利于这种病原体单独引发病害，因此我们研究了这两种病原体之间相互作用的可能性。在温室试验中，五个甜菜品种中有四个在同时接种两种病原体时比单独接种任何一种病原体时表现出更严重的根腐症状。这种协同作用发生在不利于匍枝根霉引发病害的条件下。宿主对丝核菌冠腐和根腐病的抗性降低了病害的严重程度，但当两种病原体都存在时，不足以控制病害。这引发了对正确病害诊断和管理措施的担忧，并表明根腐病复合体可能在密歇根州的甜菜种植中很重要。
