Leuconostoc spp. associated with root rot in sugar beet and their interaction with rhizoctonia solani

Authors: Strausbaugh, Carl

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/29/2015
Publication Date: 4/29/2016
Publication URL: http://handle.nal.usda.gov/10113/62370
Citation: Strausbaugh, C.A. 2016. Leuconostoc spp. associated with root rot in sugar beet and their interaction with rhizoctonia solani. Phytopathology. 106:432-441.

Interpretive Summary: Rhizoctonia root and crown rot (RRCR) caused by Rhizoctonia solani can lead to yield losses of 50% or more in commercial sugar beet fields, affect sucrose losses in stored roots, and lead to difficulties in factory processing. Management of RRCR with crop rotation and fungicide applications helps limit problems, but unacceptable levels of rot still occur. Host resistance would be the most desirable control measure, but most commercial cultivars contain only low levels of resistance. Observations from both research and commercial fields suggested that a synergistic interaction between Leuconostoc and R. solani might exist which leads to more rot than when either pathogen is present alone. To investigate this interaction, 203 Leuconostoc isolates were collected across the Amalgamated Sugar Co. production area from recently harvested roots during 2010 and 2012. The predominant Leuconstoc sp. found was L. mesenteroides, but L. pseudomesenteroides, L. kimchi, and a few isolates that may represent novel species were also found. In pathogenicity field studies with commercial sugar beet cultivar B-7, all Leuconostoc isolates had more rot when combined with R. solani than when inoculated alone both years. Also, 46 of the 52 combination treatments over the two years, had significantly more rot than the fungal check. Therefore, the data support that a synergistic interaction leads to more rot when both Leconostoc and R. solani are present in sugar beet roots.

Technical Abstract: Rhizoctonia root and crown is an important disease problem in sugar beet caused by Rhizoctonia solani and also shown to be associated with Leuconostoc. Since, the initial Leuconostoc studies were conducted with only a few isolates and the relationship of Leuconostoc with R. solani is poorly understood, a more thorough investigation was conducted. A total of 203 Leuconostoc isolates were collected from recently harvested sugar beet roots in southern Idaho and southeastern Oregon during 2010 and 2012: 88 and 85% L. mesenteroides, 6 and 15% L. pseudomesenteroides, 2 and 0% L. kimchi, and 4 and 0% unrecognized Leuconostoc sp., respectively. Based on 16S rRNA sequencing, haplotype 11 (L. mesenteroides isolates) comprised 68 to 70% of the isolates both years. In pathogenicity field studies with commercial sugar beet cultivar B-7, all Leuconostoc isolates had more rot (P <0.0001; alpha = 0.05) when combined with R. solani than when inoculated alone both years. Also, 46 of the 52 combination treatments over the two years, had significantly more rot (P <0.0001; alpha = 0.05) than the fungal check. Therefore, the data support that a synergistic interaction leads to more rot when both Leconostoc and R. solani are present in sugar beet roots.