Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 1, 2012
Publication Date: January 1, 2013
Citation: Strausbaugh, C.A., Eujayl, I.A., Foote, P. 2013. Selection for resistance to the rhizoctonia-bacterial root rot complex in sugar beet. Plant Disease. 97:93-100. Interpretive Summary: Rhizoctonia root rot caused by Rhizoctonia solani is of considerable concern in sugar beet production areas. Rhizoctonia root rot can reduce yield by 50% or more, but also seems to be on the increase and can be associated with losses in storage. In Idaho, Rhizoctonia root rot is frequently accompanied by a bacterial root rot caused by Leuconostoc mesenteroides. Previous studies focused only on resistance to Rhizoctonia root rot and not the rot complex. The most reliable results for identifying resistance to this complex came from evaluating the rot on the root surface in field studies. Evaluating the amount root tissue rotted internally for both fungal and bacterial rot did not allow for as good a cultivar separation for resistance. Studies in the greenhouse with mature roots from the field allowed for cultivar separation for resistance, but gave a storage response and did not relate to rot in the field. Thus to evaluate for resistance to Rhizoctonia root rot in the field, studies with roots inoculated in the field will have to be conducted.
Technical Abstract: The Rhizoctonia-bacterial root rot complex continues to be a concerning problem in sugar beet production areas. To investigate resistance to this complex in 26 commercial sugar beet cultivars, field studies and greenhouse studies with mature roots from the field were conducted with Rhizoctonia solani AG-2-2 IIIB strains and Leuconostoc mesenteroides. Based on means for the 26 cultivars in the 2010 and 2011 field studies, fungal rot ranged from 0 to 8%, bacterial rot ranged from 0 to 37%, total rot ranged from 0 to 44%, and surface rot ranged from 0 to 52%. All four rot variables resulted in significant (P < 0.0001) cultivar differences. Based on regression analysis, strong positive relationships (r2 from 0.6628 to 0.9320; P < 0.0001) were present among the rot variables. When ranking cultivars, the most consistent rot variable was surface rot, since 12 out of 13 variable-year combinations had significant (P < 0.05) correlations. When cultivar ranking in the greenhouse assays were compared, there was frequently a good positive correlation with storage data but when compared with field results there was no relationship. Thus with this root rot complex, the greenhouse assays related to storage and did not substitute for conducting field screening.