ARS | Publication request: Sugar beet root rot at harvest in the U.S. Intermountain West

Submitted to: Canadian Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 27, 2009
Publication Date: June 1, 2009
Citation: Strausbaugh, C.A., Gillen, A.M. 2009. Sugar Beet Root Rot at Harvest in the U.S. Intermountain West. Canadian Journal of Plant Pathology. 31:232-240.

Interpretive Summary: Root rot on sugar beet can cause considerable losses worldwide. In an effort to explain why root rots are on the increase in some sugar beet production areas of the Intermountain West (IMW), rotting roots were collected from across this region. When only fungi were isolated from roots, only 6% of the root area on individual roots was rotted. However, 71 and 68% of the root area was rotted when bacteria were found individually or with other organisms, respectively. Although the fungi were frequently present, they appeared to be responsible for only a low percentage of the overall rot, but may facilitate bacterial establishment in the root. Rhizoctonia root rot has been the primary focus for breeding efforts in the IMW. However, given the high percentage of rot associated with bacteria, bacterial root rot should also be addressed by breeding efforts.

Technical Abstract: Root rot in sugar beet causes significant losses worldwide. To assess the distribution of root rot fungi and their relationship to bacterial root rot, commercial sugar beet roots were collected at harvest time in the Intermountain West. Isolations for both fungi and bacteria were conducted using standard microbiological techniques and the root area rotted was assessed. A subset of fungal isolates was tested for pathogenicity in greenhouse assays. In the field survey, root rot averaged 6% for individual roots when fungi were isolated individually, while root rot averaged 71 and 68% when bacteria were isolated individually or in combination with other organisms, respectively. Fungi frequently associated with root rot included Rhizoctonia solani, Geotrichum spp., Fusarium spp. (F. oxysporum, F. acuminatum, F. culmorum, and F. equiseti), Mucor spp., Phoma betae, and oomycetes. However, only R. solani isolate F321 consistently caused rot in greenhouse pathogenicity tests. Lactic acid bacteria (primarily Leuconostoc and Lactobacillus) were the most frequently isolated bacteria from roots with a wet-bacterial rot. Traditionally fungal root rots have been the main focus of breeding programs, but with the larger root area rotted by lactic acid bacteria, especially Leuconostoc, these bacteria should not be ignored in breeding efforts.