Submitted to: International Sugar Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/16/2011
Publication Date: 9/1/2011
Citation: Hanson, L.E., McGrath, J.M. 2011. Rhizoctonia seedling disease on sugar beet. International Sugar Journal. 113(1352):584-589.
Interpretive Summary: Seedling damping-off can cause losses in sugar beet production. One major cause of seedling damping-off is the fungus, Rhizoctonia solani. This same pathogen can cause a root rot later in the season that is one of the most important root diseases of beet. The pathogen has several subgroups, of which AG-4 historically has been the primary type associated with damping-off while AG2-2 is the major cause of mature plant root rot. Tolerance to mature plant root rot has been developed, but much of this tolerance is not reflected by reduced damping-off. In this study, the subgroups of R. solani associated with seedlings in the Michigan Sugar growing area was found to be approximately 80% AG-2-2. This is in contrast with older reports of primarily AG-4, and can affect disease screening and disease management efforts. USDA germplasm was identified that shows varied response to AG-2-2 isolates at the seedling stage, including potential seedling disease tolerance. This tolerance was found in greenhouse screens and confirmed in field tests, raisinig the possibility of adding host plant resistance to the management options for Rhizoctonia damping-off in the future.
Technical Abstract: Rhizoctonia seedling damping-off can cause losses in sugar beet as well as providing inoculum for later root rot. The disease is caused by Rhizoctonia solani. The pathogen has several subgroups, anastomosis groups (AG), of which AG-4 has historically been associated with damping-off, while AG-2-2 is the major cause of mature plant root rot. Recently little AG-4 had been isolated in Michigan, although damping-off was occurring. In this work, the subgroups of R. solani associated with seedlings in the Michigan Sugar growing area was investigated, and approximately 80% of seedling isolates were found to be AG-2-2. Germplasm was identified that varies in response to AG-2-2 isolates which may provide additional options for damping-off management in the future.