Strausbaugh, C. A., Eujayl, I. A., and Foote, P. 2013. Selection for resistance to the Rhizoctonia-bacterial root rot complex in sugar beet. Plant Dis. 97:93-100.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 anastomosis group 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 internal 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 (r 2 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, because 12 of 13 variable-year combinations had significant (P ≤ 0.05) correlations. When cultivar ranking in greenhouse assays was compared, there was frequently a positive correlation with storage data but no relationship with field results. Thus, the greenhouse assays will identify storage rot resistance but field screening will be required to find resistance to this rot complex in the field.Rhizoctonia root rot caused by Rhizoctonia solani Kühn is of considerable concern in sugar beet production areas in the United States and other areas of the world (9,15,38). Rhizoctonia root rot can lead to root yield losses of 50% or more but also seems to be on the increase and can be associated with losses in storage (9,21,27,38,41,43). In Idaho, Rhizoctonia root rot on mature roots tends to be associated with the R. solani anastomosis group (AG) 2-2 IIIB strains and is frequently accompanied by a bacterial root rot caused by Leuconostoc mesenteroides subsp. dextranicum (Beijerinck) Garvie which leads to a Rhizoctonia-bacterial root rot complex (36,38,39). The prevalence of this rot complex seems to be favored by warmer longer-season production areas, poor crop rotation, and surface irrigations (38,40).The fungus R. solani survives from season to season as propagules in the soil or as mycelia in infested organic matter, while L. mesenteroides is widely distributed throughout the environment (11,13,19,39). The genus Leuconostoc is a gram-positive heterofermentative lactic acid bacterium commonly found in soils, sugar factories, fermenting vegetables, dairy products, manure, and wine (4,11,12,16,19,28,35,47). These bacteria are known to be important in the initial phase of fermentation but usually are superseded by other bacteria and yeast (2,6,16). A number of other bacteria and yeast associated with bacterial root rot in sugar beet roots do not cause rot on their own but will slow down rot caused by L. mesenteroides and inhibit R. solani (25,39). These bacteria and yeast in competition wi...

To reduce storage losses and improve resistance to rhizomania caused by Beet necrotic yellow vein virus (BNYVV), studies were initiated to establish a storage cultivar selection program. In 2006 and 2007, 30 or more commercial sugar beet (Beta vulgaris) cultivars were grown in soil naturally infested with BNYVV. At harvest, two root samples from each plot were collected and used to establish percent sugar. Additional samples were placed on top of an indoor pile (set point 1.7°C) and inside an outdoor pile in a randomized complete block design with four replications. After 142 and 159 days in indoor storage, sucrose reduction ranged from 13 to 90% in 2007 and 57 to 100% in 2008. Outdoor storage sucrose reduction ranged from 13 to 32% in 2007 and 28 to 60% in 2008. An average of 31 and 45% of the root surface was covered with fungal growth in 2007 and 2008, respectively. Cultivars that retained the most sucrose had resistance to BNYVV and the least fungal growth and weight loss. Indoor storage with BNYVV-infested roots allowed for the most consistent cultivar separation and will potentially lead to selection of cultivars for improved storability and rhizomania resistance.

Insect feeding and vectoring of viruses cause serious problems in sugarbeet (Beta vulgaris L.) production worldwide. In order to ameliorate insects and diseases on sugarbeet, two seed treatments, Poncho Beta (60 g a.i. [active ingredient] clothianidin + 8 g a.i. beta-cyfluthrin/100,000 seeds) and Cruiser Tef (60 g a.i. thiamethoxam + 8 g a.i. tefluthrin/100,000 seeds) were investigated in a series of five field trials from 2006 to 2009. The two seed treatments and an untreated check were tested on commercial sugarbeet cultivars in a randomized complete block design with eight replications. Insect incidence and curly top symptoms were evaluated. Both Poncho Beta and Cruiser Tef provided significant reduction in curly top symptoms and incidence of leafminers (Pegomya spp.), black bean aphid (Aphis fabae Scopoli), and sugarbeet root aphid (Pemphigus betae Doane). In the two trials conducted under curly top pressure, Poncho Beta and Cruiser Tef had more root yield than the untreated check by 3.4 to 15.1 t/ha. In the three trials without curly top pressure, Poncho Beta and Cruiser Tef resulted in root yield increases of 3.1 to 6.7 t/ha over that of the untreated check. Neonicotinoid seed treatments play an important role in early season disease and insect management in sugarbeet production, but should be viewed as a supplement to host plant resistance rather than a substitute for it.

Nitrogen (N) management is critical in sugarbeet production to optimize yield and quality. Although, past research has been critical to improving and understanding sugarbeet N nutrition, continued research is needed to evaluate evolving varieties and management practices.

A Rhizoctonia-bacterial root rot complex can lead to yield loss in the field but rots also have the potential to cause sucrose loss in storage. Thus, studies were conducted to investigate if combining sugarbeet roots suffering from this complex with healthy roots would compromise the ability of the healthy roots to retain sucrose. Over a three year period, root samples from three commercial cultivars were compared in storage as a healthy (eight healthy roots) or mixed (eight healthy roots + one rotted root) treatment inside an outdoor storage pile. The experiment was arranged as a split block (healthy in one half of block and mixed in the other) with the whole blocks arranged in a randomized complete block design with four replications. Treatments were sampled in December, January, and February and evaluated for discolored and frozen root area, weight loss, and sucrose reduction and recovery. When comparing the healthy to the mixed treatment over the nine year x sampling date combinations, the Wilcoxon signed-rank test indicated the median change for discoloration (7% increase), frozen area (14% increase), sucrose loss (5% loss), and recoverable sucrose (689 kg/ha less or 8% reduction) were significantly different from zero (P = 0.008, 0.031, 0.007, and 0.008, respectively). These data indicate that the Rhizoctonia-bacterial root rot complex can negatively affect neighboring healthy roots in storage leading to additional sucrose losses.