Interaction of Sugarbeet Host Resistance and Rhizoctonia Solani Ag-2-2 Iiib Strains

Abstract

Rhizoctonia crown and root rot caused by Rhizoctonia solani can cause serious economic losses in sugar beet fields. Preliminary evidence suggests that there could be interactions between different strains and resistance sources. Thus, field studies were conducted to determine whether nine R. solani AG-2-2 IIIB strains varied for virulence when compared with a noninoculated check and interacted with five sugar beet lines (four resistant lines and a susceptible check). The studies were arranged in a randomized complete block design with six replications. Roots were evaluated for surface rot and internal fungal and bacterial rot in September. All strains were virulent on the susceptible check, FC901/C817, and had a similar ranking (r = 0.80 to 0.97; P = 0.0096 to <0.0001) regardless of disease variable. Line FC709-2 was resistant (response not different from noninoculated check, P ≥ 0.1042) to all strains, while the strain responses resulted in weak interactions with less-resistant lines in 14 of 19 variable-year combinations. Because most commercial sugar beet cultivars contain low to intermediate resistance to Rhizoctonia crown and root rot, the strain used to screen should be considered in order to maintain consistent responses between nurseries and commercial fields. Rhizoctonia crown and root rot caused by Rhizoctonia solaniKühn can lead to yield losses of 50% or more in commercial sugar beet (Beta vulgaris L.) fields, affect sucrose losses in stored roots, and lead to difficulties in factory processing (6,17,33,36,39). Because R. solani strains form a species complex, strains have been further classified into subgroups known as anastomosis groups (AGs) and intraspecific groups (ISGs) (8,11,30). In Idaho, R. solani AG-2-2 IIIB is the primary AG and ISG associated with the most damaging rot in mature sugar beet roots (33). Recent Idaho studies have shown that the fungus is primarily limited to damaging the outer 3 to 5% of the root mass, while subsequent bacterial rot led by Leuconostoc mesenteroides subsp. dextranicum (Beijerinck) Garvie frequently invades the tissue, leading to 70% or more of the root being rotted (31,32,34,35). Because Rhizoctonia crown and root rot appears to be on the increase in a number of growing areas worldwide, developing management options for this disease is an important concern (4,5,10,22).Management of Rhizoctonia crown and root rot with crop rotation (4,5,9,19,26,28) and fungicide applications (2,17,18,37,41) helps limit problems but unacceptable levels of rot still frequently occur (2). Host resistance would be the most desirable control measure (24), because it tends to be more cost effective than other approaches. However, most commercial cultivars provide only low to intermediate levels of resistance (32). Cultivars with higher levels of resistance often do not have the yield and resistance to other diseases (curly top, Aphanomyces root rot, Fusarium wilt, and Cercospora leaf spot) needed for cultivar approval. A number of germplasm lines with Rhizoctonia crown and root rot r...

Leuconostoc spp. Associated with Root Rot in Sugar Beet and Their Interaction with Rhizoctonia solani

“…However, most commercial sugar beet cultivars provide only low to intermediate levels of resistance (Strausbaugh et al 2013a). In addition, cultivars that do contain good resistance typically do not have the yield and resistance to other diseases necessary to make it through the cultivar approval process (Strausbaugh et al 2013b). Developing resistant cultivars is problematic, because resistance is quantitative and the cultivars frequently suffer from yield drag (Hecker and Ruppel 1975;Lein et al 2008;Panella 2005).…”

“…Also complicating the screening process for resistance in sugar beet are the different strains of R. solani and their interactions with different Leuconostoc spp. (Strausbaugh et al 2013b). The use of crop rotation (Buddemeyer et al 2004;Buhre et al 2009;Engelkes and Windels 1996;Ruppel 1985;Rush and Winter 1990) and fungicides (Bolton et al 2010;Kiewnick et al 2001;Kirk et al 2008;Stump et al 2004;Windels and Brantner 2005) can also help limit RRCR; however, unacceptable levels of rot still frequently occur.…”