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North Dakota (ND) and Minnesota (MN) are two leading sugar beet producing states in the US jointly contributing 57% of domestic production, which results in over $5 billion in total economic activities. Sugar beet plant samples that had typical wilting and root rot symptoms were collected from Hickson, ND and Foxhome, MN in 2020. A fungus was isolated from diseased roots in potato dextrose agar media and was identified as Rhizopus arrhizus (synonym: R. oryzae) based on morphological features, microscopic visualizations, and the ribosomal Internal Transcribed Spacer DNA sequence identity. The pathogenicity of the R. arrhizus isolates was checked by seed and root inoculation in the laboratory and greenhouse. In vitro inoculation of sugar beet seeds with mycelial agar plugs in PDA plates showed reduced seedling growth and emergence. In the greenhouse, seeds inoculated with young growing mycelial agar plugs showed seedling rot, wilting and abnormal growth of cotyledons when evaluated at 10 days post inoculation (dpi). Sugar beet plants at four weeks old were inoculated with fungal spore suspension by the dipping method. At 21-dpi, inoculated roots showed characteristics root rot and wilting symptoms. Re-isolated fungus from inoculated seedlings with root rot symptom was found to be identical to pure culture of the isolates retrieved from the field samples. These findings added a new insight on and better understanding of the fungus causing seedlings and root rot of sugar beet; the information generated will direct further plan of action for its management to prevent crop loss.

In this contribution, we report on a survey of leaf blight on sugar beet in the Sidney factory district of Montana caused by the soilborne fungus Sclerotinia sclerotiorum. In addition to morphological and pathological characterization of the pathogen on sugar beet, we confirmed the molecular identity of the fungus by DNA sequence analysis of the ribosomal internal transcribed spacer region. Our findings are significant because the sugar beet production in south-central and eastern Montana contributes more than $100 million in economic activities. The incidence of this emerging disease will require changes in conventional disease management.

Rhizoctonia solani is an economically important pathogen of sugar beet (Beta vulgaris L.) causing seedling damping-off, and root and crown rot. Cultural practices, partially resistant cultivars, and fungicides are among the methods most used to manage R. solani. Penicillium pinophilum, a potential biocontrol agent for Rhizoctonia damping-off, was isolated from sugar beet. Our objective was to evaluate the biocontrol potential of P. pinophilum against R. solani AG 2–2 under laboratory and greenhouse conditions. In vitro co-culture of both fungi showed that R. solani growth was inhibited by P. pinophilum. A greenhouse inoculation study was done using sclerotia of R. solani and a conidia suspension of P. pinophilum to evaluate the response of a Rhizoctonia susceptible cultivar. Treatments included R. solani sclerotia, P. pinophilum conidia suspension, a combination of R. solani sclerotia with P. pinophilum conidia suspension, and a mock inoculation with water (control). One 2-cm deep furrow was made in the middle of peat filled trays into which 10 seeds were planted. Each treatment was applied adjacent to each seed and covered with peat. There were four replicates per treatment arranged in a completely randomized design. The sole sclerotia treatment caused 75% damping-off and severe root rot on surviving plants whereas the combination of sclerotia with P. pinophilum conidia suspension reduced damping-off by 50%. No damping-off incidences were observed with the P. pinophilum conidia suspension or the mock-inoculated control. It was concluded that P. pinophilum has the potential to reduce damping-off caused by R. solani but use of the most appropriate P. pinophilum concentration and its mitigation mechanisms need further studies.

Minnesota and North Dakota combined contain 55% of the sugar beet production area in the United States, contributing to 49% of the nation’s sugar beet production in 2018. Fusarium diseases caused by Fusarium oxysporum f. betae and F. secorum on sugar beet can cause significant reduction in both root yield and sucrose concentration and purity. The objective of this research was to identify an alternative artificial inoculation method to induce Fusarium diseases on sugar beet leaves and roots caused by both Fusarium spp. in greenhouse conditions to better aid in research efforts. We tested four inoculation methods, including barley to seed, barley to root, drenching, and cutting. and compared them with the conventional root-dipping inoculation method. The inoculation method of placing Fusarium-colonized barley seed close to sugar beet seed (barley to seed) caused levels of symptom severities on both leaves and roots similar to the root-dipping method. Because the traditional root-dipping method involves a laborious transplant process, use of infected barley seed as inoculum may serve as an alternative method in the evaluation of host resistance and pathogen virulence among Fusarium diseases by Fusarium spp. on sugar beet at the seed or seedling stage.

Background Sugarbeet (Beta vulgaris L.) roots are stored under conditions that cause roots to dehydrate, which increases postharvest losses. Although exogenous jasmonate applications can reduce drought stress in intact plants, their ability to alleviate the effects of dehydration in postharvest sugarbeet roots or other stored plant products is unknown. Research was conducted to determine whether jasmonate treatment could mitigate physiological responses to dehydration in postharvest sugarbeet roots. Methods Freshly harvested sugarbeet roots were treated with 10 µM methyl jasmonate (MeJA) or water and stored under dehydrating and non-dehydrating storage conditions. Changes in fresh weight, respiration rate, wound healing, leaf regrowth, and proline metabolism of treated roots were investigated throughout eight weeks in storage. Results Dehydrating storage conditions increased root weight loss, respiration rate, and proline accumulation and prevented leaf regrowth from the root crown. Under dehydrating conditions, MeJA treatment reduced root respiration rate, but only in severely dehydrated roots. MeJA treatment also hastened wound-healing, but only in the late stages of barrier formation. MeJA treatment did not impact root weight loss or proline accumulation under dehydrating conditions or leaf regrowth under non-dehydrating conditions. Both dehydration and MeJA treatment affected expression of genes involved in proline metabolism. In dehydrated roots, proline dehydrogenase expression declined 340-fold, suggesting that dehydration-induced proline accumulation was governed by reducing proline degradation. MeJA treatment altered proline biosynthetic and catabolic gene expression, with greatest effect in non-dehydrated roots. Overall, MeJA treatment alleviated physiological manifestations of dehydration stress in stored roots, although the beneficial effects were small. Postharvest jasmonate applications, therefore, are unlikely to significantly reduce dehydration-related storage losses in sugarbeet roots.

Rhizoctonia crown and root rot of sugar beet (Beta vulgaris L.), caused by Rhizoctonia solani, continues to be one of the important concerns for the beet industry in Minnesota and North Dakota. Use of resistant cultivars is an important strategy in the management of R. solani in combination with seed treatment and timely fungicide application during the growing season. The objective of this greenhouse study was to determine how sugar beet plants responded to increasing age in resistance to R. solani. Each of three seed companies provided three commercial cultivars with varying R. solani resistance levels: susceptible, moderately resistant, and resistant. Seed were planted at a weekly interval to create different plant age groups from seed to 10-week-old plants, with growing degree days (GDD) ranging from 0 to 1,519 thermal time (°Cd). Seed and plants were all simultaneously inoculated with R. solani AG2-2-infested barley grains. Twenty-eight days after inoculation, plants were pulled and washed, and roots were evaluated for disease severity. All cultivars were highly susceptible to R. solani when inoculated at seed to 3 weeks old (0 to 464°Cd). At 4 and 5 weeks of plant age (617 to 766°Cd), resistant cultivars started to show significant resistance to R. solani. Proportion of the affected roots with disease score ≥ 5 followed a sigmoid response, declining with increased GDD in moderately resistant and resistant cultivars, whereas it continued to decline linearly with increased GDD in susceptible cultivars. This study demonstrated that sugar beet cultivars, regardless of their assigned level of R. solani resistance, were highly susceptible to the pathogen before they reached the six- to eight-leaf stage at 4 to 5 weeks (617 to 766°Cd) after planting. Therefore, additional protection in the form of seed treatment or fungicide application may be required to protect sensitive sugar beet seed and seedlings in fields with a history of R. solani under favorable environmental conditions.

Sugarbeet (Beta vulgaris) is considered as one of the most viable feedstock alternatives to maize for biofuel production since herbicide resistant sugarbeet was deregulated by the United States Department of Agriculture in 2012. So far, only a few sugarbeet simulation models have been developed and these models are limited to application for local regions. The Decision Support System for Agrotechnology Transfer (DSSAT) provides a common framework for a cropping system study and currently has crop modules for >40 crops. However, DSSAT currently does not include a model for sugarbeet. In this study, the Crop and Environment REsource Synthesis (CERES) Beet model was modified and incorporated into the current version of the Cropping System Model (CSM) to simulate growth, development, and yield of sugarbeet. The PEST optimizer was used for parameter estimation, transferability evaluation, and predictive uncertainty analysis. The sugarbeet model was evaluated with two sets of experimental data collected in two different regions and under different environmental conditions; one in Romania (Southeastern Europe) during 1997–1998 and the other in North Dakota, US (North America) during 2014–2016. After model calibration for specific cultivars, the CSM-CERES-Beet model performed well for the simulation of leaf area index, leaf number, leaf or top weight, and root weight for both datasets (NSE = 0.144–0.976, rRMSE = 0.127–1.014). Uncertainty analysis revealed that the calibrated CSM-CERES-Beet consistently over-predicted leaf number with false confidence, although measured leaf number also showed a significant variability. The model was successfully applied for predicting yield for six different sugarbeet cultivars grown in North Dakota during the 2014 to 2016 growing seasons. CSM-CERES-Beet could be applied for predicting sugarbeet yield for different soil and climatic conditions and various management scenarios for the Red River Valley in the US and other regions with environmental conditions favorable for sugarbeet production.

France was one of the earliest countries to grow sugar beet, and in 2016, it produced 382,858 ha in 10 of its northern regions to supply sugar and ethanol/alcohol. France is a top producer of sugar beet with average of over 88 tonnes of root yield ha−1 and 13.7 tonnes sugar ha−1. This paper describes the different husbandry practices involved in France producing its EU sugar quota and discussed some implications of the end of the sugar quota system in October 2017 and the need for continuous research by the Institut Technique de la Betterave to ensure that beet production continues to be efficient, profitable, and sustainable.

Minnesota is the top sugar beet (Beta vulgaris L.) producing state in the United States. In 2020, sugar beet plants were observed for the first time in which the two to three oldest leaves had light brown to dark brown necrotic leaf lesions that eventually became yellow or brown and died but remained attached to the plant. Morphological data and sequences of internal transcribed spacer regions identified the pathogen as Sclerotinia sclerotiorum. Because over 90% of the plants in identified fields were infected it was difficult to quantify loss in yield or quality caused by this disease. All fields with symptomatic plants had soybean or edible beans in the rotation. One field planted to several different varieties indicated that all the varieties were symptomatic. It will be useful to determine any economic loss caused by S. sclerotiorum and any known varietal resistance to this pathogen.

In May 2019, sugar beet (Beta vulgaris L.) seedlings with symptoms of wilting and root tip discoloration and necrosis were found in Moorhead (46.5507° N, 96.4208° W), Minnesota, USA. Roots of infected seedlings were surface sterilized with 10% bleach for 15 seconds, rinsed with sterile distilled water and cultured on water agar (MA Mooragar®, Inc, CA) for 3 days at 23 ± 2°C. Isolates were transferred to carnation leaf agar (CLA) and incubated at room temperature (22°C) under fluorescent light for 14 days. Abundant macroconidia were produced in sporodochia. Macroconidia were 5- to 7-septate, slightly curved at the apex, and ranged from 35 to 110 ×1.2 to 3.8 μm. No microconidia were produced. Chlamydospores with thick, roughened walls were observed in chains or in clumps, and were ellipsoidal or subglobose. Single spore was transferred from CLA to potato dextrose agar (HIMEDIA Laboratories, India) produced abundant white mycelium and was pale brown where the colony was in contact with the media. The morphological features of the isolates were consistent with Fusarium equiseti (Corda) Sacc. (Leslie and Summerell 2006, Li et al. 2015). Genomic DNAs (NORGEN BIOTEK CORP, Fungi DNA Isolation Kit #26200) of two representative isolates were used for polymerase chain reaction (PCR). The second largest subunit of RNA polymerase (RPB2) was amplified by PCR with primers 5f2/7cr (O'Donnell et al. 2010). The amplified PCR product was sequenced and deposited in GenBank (accession number MW048778). A BLAST search in Genbank and the Fusarium MLST database showed 100% sequence alignment to F. equiseti with accession MK077037.1 and NRRL 25795, respectively. Pathogenicity testing was done using three sugar beet seedlings (Hilleshog proprietary material, Hilleshog Seed, LLC, Halsey, OR 97348) at cotyledonary stage grown in a pot (4˝×4˝×6˝) with six replicates. Seedlings were inoculated with F. equiseti conidial suspension (104 conidia ml-1 for 8 minutes) by the root dip method (Hanson, 2006). Mock inoculated plants were dipped in sterile water. Inoculated and control plants were placed in the greenhouse at 25 ± 2°C, and 75 to 85% relative humidity. One week later, inoculated seedlings showed root tip tissue discoloration similar to those observed in the field and non-inoculated seedlings were symptomless. This study was repeated. The fungus was re-isolated from diseased roots and confirmed to be F. equiseti based on morphological characters. Fusarium equiseti was reported on freshly harvested and stored beet in Europe but was not found to be pathogenic (Christ et al. 2011). Strausbaugh and Gillen (2009) reported the association of F. equiseti and root rot of sugar beet but did not report pathogenicity. This pathogen is reported in several crops including edible beans that is grown in rotation with sugar beet in several production areas (Jacobs et al. 2018). The most important Fusarium species reported to cause significant economic damage to sugar beet include F. oxysporum and F. secorum (Secor et al. 2014, Webb et. al. 2012). The presence of another pathogenic Fusarium species in sugar beet will require monitoring to determine how widespread it is and whether current commercial cultivars are resistant. To our knowledge, this is the first report of F. equiseti causing disease on sugar beet seedlings in Minnesota, USA.

Rhizoctonia solani Kuhn is a major soil-borne pathogen limiting sugar beet ( Beta vulgaris L.) production in the United States and other countries worldwide. There is no commercial cultivar which is immune from infection by R. solani and highly resistant cultivars typically have a yield penalty. Growers use cultivars with some levels of resistance and rely on the timely application of fungicides to control R. solani . Azoxystrobin (Quadris ® ) has been the most widely used fungicide for control of R. solani on sugar beet since its registration in the United States in 1997. In 2015, growers wanted to know whether generic azoxystrobin, which became available on the market and at a lower price than Quadris ® , would provide effective control of R. solani . The objectives of this greenhouse study were to evaluate the efficacy and safety of generic azoxystrobins at controlling R. solani on sugar beet compared to the industry's standard Quadris. Three generic azoxystrobins – Satori ® , Aframe™ and Equation™ - and two application methods - in-furrow at planting and band applications to 4-leaf stage sugar beet - were evaluated. Inoculation with R. solani AG 2-2IIIB was done after fungicide applications. To check for phytotoxicity, fungicides were applied but with mock inoculation. Plant survivors, plant height, root weight and disease severity were evaluated. Results indicated that the generic azoxystrobins were safe to use on sugar beet seeds and plants and provided similar disease control of R. solani as the industry's standard Quadris treatment. This study demonstrated under greenhouse conditions that Satori ® , Aframe™ and Equation™ have the potential to be used by growers for disease management in sugar beet fields with a history of R. solani .

Rhizoctonia damping-off and crown and root rot caused by Rhizoctonia solani are major diseases of sugar beet (Beta vulgaris L.) worldwide, and growers in the United States rely on fungicides for disease management. Sensitivity of R. solani to fungicides was evaluated in vitro using a mycelial radial growth assay and by evaluating disease severity on R. solani AG 2-2 inoculated plants treated with fungicides in the greenhouse. The mean concentration that caused 50% mycelial growth inhibition (EC50) values for baseline isolates (collected before the fungicides were registered for sugar beet) were 49.7, 97.1, 0.3, 0.2, and 0.9 μg ml−1 and for nonbaseline isolates (collected after registration and use of fungicides) were 296.1, 341.7, 0.9, 0.2, and 0.6 μg ml−1 for azoxystrobin, trifloxystrobin, pyraclostrobin, penthiopyrad, and prothioconazole, respectively. The mean EC50 values of azoxystrobin, trifloxystrobin, and pyraclostrobin significantly increased in the nonbaseline isolates compared with baseline isolates, with a resistant factor of 6.0, 3.5, and 3.0, respectively. Frequency of isolates with EC50 values >10 μg ml−1 for azoxystrobin and trifloxystrobin increased from 25% in baseline isolates to 80% in nonbaseline isolates. Although sensitivity of nonbaseline isolates of R. solani to quinone outside inhibitors decreased, these fungicides at labeled rates were still effective at controlling the pathogen under greenhouse conditions.

Rhizoctonia crown and root rot of sugar beet (

Beet necrotic yellow vein virus (BNYVV) is the causal agent of rhizomania, a disease of global importance to the sugar beet industry. The most widely implemented resistance gene to rhizomania to date is Rz1, but resistance has been circumvented by resistance-breaking (RB) isolates worldwide. In an effort to gain greater understanding of the distribution of BNYVV and the nature of RB isolates in Minnesota and eastern North Dakota, sugar beet plants were grown in 594 soil samples obtained from production fields and subsequently were analyzed for the presence of BNYVV as well as coding variability in the viral P25 gene, the gene previously implicated in the RB pathotype. Baiting of virus from the soil with sugar beet varieties possessing no known resistance to rhizomania resulted in a disease incidence level of 10.6% in the region examined. Parallel baiting analysis of sugar beet genotypes possessing Rz1, the more recently introgressed Rz2, and with the combination of Rz1 + Rz2 resulted in a disease incidence level of 4.2, 1.0, and 0.8%, respectively. Virus sequences recovered from sugar beet bait plants possessing resistance genes Rz1 and/or Rz2 exhibited reduced genetic diversity in the P25 gene relative to those recovered from the susceptible genotype while confirming the hypervariable nature of the coding for amino acids (AAs) at position 67 and 68 in the P25 protein. In contrast to previous reports, we did not find an association between any one specific AA signature at these positions and the ability to circumvent Rz1-mediated resistance. The data document ongoing virulence development in BNYVV populations to previously resistant varieties and provide a baseline for the analysis of genetic change in the virus population that may accompany the implementation of new resistance genes to manage rhizomania.

In 2002, somel sugar beet (Beta vulgaris L.) fields in the Red River Valley (RRV) of Minnesota and North Dakota had symptoms characteristic of Fusarium yellows (4). In 2004, ≈5% of fields in the RRV had symptomatic plants. Interveinal yellowing of older leaves typically began in mid-July and as the disease progressed, younger leaves turned yellow. Sometimes, one side of the leaf was yellow or necrotic while the other side remained green. As leaves died, they remained attached to the crown. Transverse sections of roots revealed a light gray-brown discoloration of the vascular tissue but no external rotting of roots. Isolations from 35 symptomatic roots collected in eight fields yielded 25 isolates identified as F. oxysporum (from single conidia grown on homemade potato dextrose agar and carnation leaf agar) (3). Pathogenicity was determined by dipping roots of 5-week-old sugar beet plants (cv. ACH 9363) in a suspension of 104 conidia per ml for 8 min (12 isolates, 10 to 12 plants per isolate). Plants were planted in Cone-tainers (3.8 cm diameter × 21 cm; Stuewe and Sons, Inc. Corvallis, OR) containing sterile soil. Three known cultures of F. oxysporum Schlecht. emend. Snyd. & Hans. f. sp. betae Stewart (= F. conglutinans var. betae Stewart [4]) also were included (13 and 216c from L. Hanson, USDA-ARS, Fort Collins, CO; 0-1122 from The Pennyslvania State University Fusarium Research Center). The control was sterile water. Plants were placed in a greenhouse at 24 to 27°C with natural light supplemented with illumination from high-pressure sodium-vapor lamps for 16 h daily and lightly fertilized biweekly to avoid chlorosis from nutrient deficiency. After 6 to 7 weeks, plants were rated for disease on a 0 to 4 scale: 0 = no disease; 1 = slight to extreme plant stunting, leaves may be wilted; 2 = chlorotic leaves, some with necrosis at margins; 3 = tap root dried and brown to black in color, leaves dying; and 4 = plant dead (1). The experiment was repeated. Disease severity differed between trials, but all isolates of F. oxysporum and F. oxysporum f. sp. betae resulted in disease ratings statistically (P < 0.05) greater than that of the water control. In Trial 1, isolates of F. oxysporum averaged a rating of 2.1 (range of 1.8 to 3.3) and F. oxysporum f. sp. betae averaged 2.1 (range of 2.0 to 2.2) compared with 0.1 for the water control. One isolate of F. oxysporum had a statistically higher rating than did the cultures of F. oxysporum f. sp. betae. In Trial 2, isolates of F. oxysporum averaged a rating of 3.3 (range of 2.7 to 3.7) and F. oxysporum f. sp. betae averaged 3.1 (range of 2.7 to 3.4) compared with 0.2 for the water control. Cultures of F. oxysporum (8 of 12) resulted in ratings statistically higher than that of the least pathogenic culture of F. oxysporum f. sp. betae. Cultures of F. oxysporum and F. oxysporum f. sp. betae recovered from inoculated plants were identical to those used to inoculate plants. To our knowledge, this is the first report of F. oxysporum f. sp. betae on sugar beet in the Red River Valley of Minnesota and North Dakota. The disease has been reported in California, Colorado, Montana, Nebraska, Oregon, Texas, and Wyoming (1,2). References: (1) R. A. Cramer et al. J. Phytopathol. 151:352, 2003. (2) G. A. Fisher and J. S. Gerik. Phytopathology 84:1098, 1994. (3) P. E. Nelson et al. Fusarium Species: An illustrated Manual for Identification. The Pennsylvania State University Press. University Park, 1983. (4) D. Stewart. Phytopathology 21:59, 1931.

Visual assessments of disease severity are currently the industry standard for quantification of the necrosis caused by Cercospora beticola on sugar beet (Beta vulgaris) leaves. We compared the precision, reproducibility, and sensitivity of a multispectral radiometer to visual disease assessments. Individual wavebands from the radiometer, as well as vegetative indices calculated from the individual wavebands, were compared with visual disease estimates from two raters at each of two research sites. Visual assessments and radiometric measurements were partially repeated immediately after the first assessment at each site. Precision, as measured by reduced coefficients of variation, was improved for all vegetative indices and individual waveband radiometric measures compared with visual assessments. Visual assessments, near-infrared singlewaveband reflectance values, and four of the six vegetative indices had high treatment F values, suggesting greater sensitivity at discriminating disease severity levels. Reproducibility, as measured by a test-retest method, was high for visual assessments, single-waveband reflectance at 810 nm, and several of the vegetative indices. The use of radiometric methods has the potential to increase the precision of assessments of Cercospora leaf spot foliar symptoms of sugar beet while eliminating potential bias. We recommend this method be used in conjunction with visual disease assessments to improve precision of assessments and guard against potential bias in evaluations.

Powdery mildew caused by Erysiphe polygoni was widespread on sugar beet (Beta vulgaris) in North Dakota during 2006. This disease is generally not prevalent in the state because of the application of fungicides, which also have efficacy against powdery mildew, for control of Cercospora leaf spot caused by Cercospora beticola. Because Cercospora leaf spot pressure was low in 2006, fewer fungicide applications were made in the state, thus allowing for more observations of powdery mildew. Leaf samples from four fields near Amenia, Minto, Prosper, and St. Thomas, ND were collected in mid-September to look for the perfect stage of E. polygoni, since this has recently been observed in Idaho, Colorado, Montana, and Nebraska (1–3). Only the leaves collected from the field near Amenia had visible immature (yellow and brown) globose ascomata; ascomata were not observed on the leaves collected in the other fields. Additional leaves were collected from the field near Amenia in early October; these leaves had immature and mature (black) globose ascomata that were 70 to 105 μm in diameter. Mature ascomata contained ovoid to elliptic asci with one to four hyaline-to-golden pigmented ascospores (20 to 25 × 12 to 20 μm). The color, shape, and size of ascomata, asci, and ascospores were similar to previously reported observations (1–4). The prevalence of the perfect stage in North Dakota is unknown, since no statewide surveys were conducted. To our knowledge, this is the first report of the perfect stage of E. polygoni on sugar beet in North Dakota. The occurrence of the perfect stage could lead to a means for overwintering in this area. Because of the means for genetic recombination, the risk of fungicide resistance and the development of races may increase. References: (1) J. J. Gallian and L. E. Hanson. Plant Dis. 87:200, 2003. (2) R. M. Harveson. Plant Dis. 88:1049, 2004. (3) B. Jacobsen et al. Plant Dis. 89:1362, 2005. (4) E. G. Ruppel. Powdery mildew. Pages 13–15 in: Compendium of Beet Diseases and Insects. E. D. Whitney and J. E. Duffus, eds. The American Phytopathological Society. St. Paul, MN, 1986.

In the United States, yellows disease of sugar beet (Beta vulgaris), which causes wilt, early death, and yield reduction, is caused primarily by Fusarium oxysporum f. sp. betae (3,4), but F. graminearum (2) has also been implicated. During the past 3 years, a similar disease causing yellowing and severe decline appeared in some sugar beet fields of central and southwest Minnesota planted with cultivars resistant to yellows. The disease has become a concern to the local sugar beet industry, which produces 56% of sugar beets in the United States. From 2005 to 2007, isolations were made from sugar beets collected in commercial fields and from a Fusarium screening nursery showing symptoms of yellowing, interveinal chlorosis, scorching, stunting, vascular discoloration of the taproot, and early death of plants. Of 96 Fusarium isolates recovered and used in root-dip inoculation trials in the greenhouse, 58 were pathogenic to sugar beets. On the basis of morphology, 12 were identified as F. oxysporum, 6 as F. graminearum, and 40 as a novel Fusarium species. The remaining 38 isolates were nonpathogenic. All three pathogenic Fusarium species were isolated from taproots, but only the novel Fusarium was isolated from petioles. In culture, the novel Fusarium exhibited a bright orange color on the underside of potato dextrose agar medium and produced micro- and macroconidia sparsely. Hyphal tip isolates of all novel Fusarium isolates were pathogenic, causing typical yellowing symptoms and plant death to the Fusarium yellows susceptible sugar beet cv. VDH46177 in replicated greenhouse trials. Isolates were successfully reisolated from the symptomatic plants, fulfilling Koch's postulates. Restriction fragment length polymorphism (RFLP) endonuclease digestion patterns (Alu1, Fnu4HI, HaeIII, and HhaI) of the internal transcribed spacer (ITS) region of 40 pathogenic novel isolates showed a distinct pattern compared with known Fusarium species. Thin layer chromatography analysis of 13 novel isolates detected the type A trichothecenes neosolaniol and 4,15-diacetoxyscirpenol. Partial sequences of the translation elongation factor 1-α (TEF) from 12 single-spored novel Fusarium isolates were generated. BLAST analysis of the TEF sequence against the FUSARIUM-ID (1) and GenBank databases did not match any known Fusarium species. On the basis of pathogenicity, morphology, RFLP patterns, mycotoxin production, and TEF sequence analysis it appears that this is a new species of Fusarium, but additional multilocus phylogenetic analyses are warranted. The natural occurrence of this novel Fusarium pathogen in sugar beet may have implications in breeding for resistance to Fusarium yellows, since yellow decline has been observed in purportedly Fusarium-tolerant cultivars in the Minnesota and North Dakota production regions. References: (1) D. M. Geiser et al. Eur. J. Plant Pathol. 110:473, 2004. (2) L. E. Hanson. Plant Dis. 90:686, 2006. (3). L. E. Hanson. Plant Dis. 90:1554, 2006. (4) C. E. Windels et al. Plant Dis. 89:341, 2005.

Cercospora leaf spot, caused by the fungus Cercospora beticola Sacc., is the most serious and important foliar disease of sugar beet (Beta vulgaris L.) wherever it is grown worldwide. Cercospora leaf spot first caused economic damage in North Dakota and Minnesota in 1980, and the disease is now endemic. This is the largest production area for sugar beet in the United States, producing 5.5 to 6.0 million metric tons on approximately 300,000 ha, which is 56% of the sugar beet production in the United States. This Plant Disease feature article details a cooperative effort among the participants in the sugar beet industry in this growing area and represents a successful collaboration and team effort to confront and change a fungicide resistance crisis to a fungicide success program. As a case study of success for managing fungicide resistance, it will serve as an example to other pathogen–fungicide systems and provide inspiration and ideas for long-term disease management by fungicides.

Cercospora leaf spot (CLS) of sugar beet is caused by the fungus Cercospora beticola. CLS management practices include the application of the sterol demethylation inhibitor (DMI) fungicides tetraconazole, difenoconazole, and prothioconazole. Evaluating resistance to DMIs is a major focus for CLS fungicide resistance management. Isolates were collected in 1997 and 1998 (baseline sensitivity to tetraconazole, prothioconazole, or difenoconazole) and 2007 through 2010 from the major sugar-beet-growing regions of Minnesota and North Dakota and assessed for in vitro sensitivity to two or three DMI fungicides. Most (47%) isolates collected in 1997–98 exhibited 50% effective concentration (EC50) values for tetraconazole of –1, whereas no isolates could be found in this EC50 range in 2010. Since 2007, annual median and mean tetraconazole EC50 values have generally been increasing, and the frequency of isolates with EC50 values >0.11 μg ml–1 increased from 2008 to 2010. In contrast, the frequency of isolates with EC50 values for prothioconazole of >1.0 μg ml–1 has been decreasing since 2007. Annual median difenoconazole EC50 values appears to be stable, although annual mean EC50 values generally have been increasing for this fungicide. Although EC50 values are important for gauging fungicide sensitivity trends, a rigorous comparison of the relationship between in vitro EC50 values and loss of fungicide efficacy in planta has not been conducted for C. beticola. To explore this, 12 isolates exhibiting a wide range of tetraconazole EC50 values were inoculated to sugar beet but no tetraconazole was applied. No relationship was found between isolate EC50 value and disease severity. To assess whether EC50 values are related to fungicide efficacy in planta, sugar beet plants were sprayed with various dilutions of Eminent, the commercial formulation of tetraconazole, and subsequently inoculated with isolates that exhibited very low, medium, or high tetraconazole EC50 values. The high EC50 isolate caused significantly more disease than isolates with medium or very low EC50 values at the field application rate and most reduced rates. Because in vitro sensitivity testing is typically carried out with the active ingredient of the commercial fungicide, we investigated whether loss of disease control was the same for tetraconazole as for the commercial product Eminent. The high EC50 isolate caused more disease on plants treated with tetraconazole than Eminent but disease severity was not different between plants inoculated with the very low EC50 isolate.

Sugar beet (Beta vulgaris L.) is a globally important crop for sugar. In May 2019, sugar beet seedlings were observed with wilting, lodging and a few were dead in Glendive (46.970170, -104.838204), Montana. Symptoms appeared near the soil line as the stem (hypocotyl) turned dark brown to black with characteristic thread-like infections which resembled Pythium damping-off. It affected approximately 10% of the growing seedlings. Diseased sugar beet root tissues were excised with a sterile scalpel and small pieces (10 mm²) were surface sterilized with 70 % ethanol for 30 seconds, rinsed twice with autoclaved water, air-dried and transferred to potato dextrose agar (PDA) media amended with pimaricin-vancomycin-PCNB (Conway, 1985). Four plates were incubated at 25° C in the dark (Masago et al., 1977) and two weeks later white, dense colony was observed (Zhang et al., 2018). The terminal smooth, globose oogonia (average 18.5 µm in diameter) and antheridia (average 14.5 × 9.5 µm) extended below the oogonium were observed via VWR N. A. 0.30 microscope. The morphological features of the four isolates were consistent with Pythium ultimum Trow (Watanabe, 2002). Genomic DNAs (NORGEN BIOTEK CORP, Fungi DNA Isolation Kit #26200) of four isolates were used for polymerase chain reaction (PCR) with the ITS6-ITS7 primers (Taheri et al., 2017). Subsequently, PCR products were flushed by E.Z.N.A ®Cycle Pure Kit, OMEGA and four samples were sent for Sanger sequencing to GenScript (GenScript, Piscataway, NJ). The sequences were identical and submitted to GenBank, NCBI (accession no. MN398593). The NCBI Blast analysis showed 100% sequence homology to Pythium ultimum with the following GenBank accessions; KF181451.1, KF181449.1 and AY598657.2. Pathogenicity test was done on sugar beet with the same isolates in the greenhouse. Two week old, pythium culture was mixed with vermiculite and perlite mixer (PRO-MIX FLX) in the plastic trays (24´´ x 15´´× 3˝), (22 °C, 75% Relaive Humidity). Sterile water (500 ml/each tray) was added in the mixer to provide sufficient moisture. Twenty seeds of cv. Hilleshog 4302 were sown in the tray, and the trays were replicated thrice with inoculated and mock treatments. Plants were watered as needed to maintain adequate soil moisture conducive for plant growth and disease development. Seven days after sowing, 50% and 100% germination was observed in the inoculated and control treatments, respectively. At the beginning of the second week, 30% post-emergence damping-off was observed in the inoculated treatments. Diseased seedlings were gently pulled out from the pots where similar symptoms were observed in the sugar beet seedlings as described previously. No incidence of disease was observed in mock-treated seedlings. Consistent reisolation of Pythium ultimum was morphologically and molecularly confirmed from the diseased seedlings, thus fulfilling Koch's postulates. Pythium spp identification is prerequisite to develop effective management of pre and post-emergence damping-off. Pythium ultimum was previously reported in Nebraska to cause sugar beet seed rot and pre-emergence damping-off (Harvenson 2006). To our knowledge, this is the first report of Pythium ultimum causing damping-off on sugar beet in the Sidney factory district in Montana.

Plant-parasitic nematodes (PPNs) are an important group of pathogens on sugarbeet. Surveys were conducted in the Red River Valley (RRV) area of North Dakota (ND) and Minnesota (MN) to determine the incidence, abundance, and distribution of PPNs in sugarbeet fields. A total of 217 soil samples were collected in 2016 and 2017 from fields with sugarbeet or a history of sugarbeet production. In addition, 48 samples were collected in 2016 from tare soils in sugarbeet piling stations, and two samples were collected in 2017 from sugarbeet production fields in eastern Montana (MT) and western ND border area. The incidence and abundance of major genera of PPNs identified from sugarbeet production fields in 2016 and 2017 were: Heterodera (incidence = 15%, abundance = 1,351/200 gm of soil); Helicotylenchus (38%, 157); Tylenchorhynchus (37%, 121); Paratylenchus (28%, 108); Pratylenchus (6%, 38); Paratrichodorus (7%, 37); Xiphinema (3%, 32); and Hoplolaimus (0.4%, 20). Helicotylenchus, Tylenchorhynchus, Paratylenchus, and Heterodera were the most frequent and widely distributed nematode genera whereas, Paratrichodorus and Pratylenchus were found less frequently and at low densities. Xiphinema and Hoplolaimus were rarely detected at lower densities. Paratylenchus and Tylenchorhynchus were widely distributed in most of the sampled counties (n = 11), followed by Helicotylenchus (10), Heterodera (8), Pratylenchus (8), Xiphinema (4), Paratrichodorus (3), and Hoplolaimus (1). Species-specific PCR assays and direct sequencing of ribosomal DNA were conducted to identify species. Species identification revealed that the cyst nematodes from one of the counties in eastern MT were Heterodera schachtii and the cyst nematodes analyzed from 31 samples in 12 counties in ND and MN were H. glycines. We have not identified any H. schachtii thus far from surveyed samples in eastern ND and western MN. Other nematode species identified include Paratrichodorus allius, Pratylenchus neglectus, Tylenchorhynchus sp., Paratylenchus nanus, Helicotylenchus microlobus, and H. pseudorobustus. Accurate identification of these nematodes and awareness of their occurrence across the region is essential for developing effective pest management strategies for improved sugarbeet production.

The soil-borne fungus Rhizoctonia solani causes damping-off on sugar beet seedlings. Growers rely on fungicides to protect sugar beet in fields affected by R. solani. Quinone outside inhibitor (QoI) fungicides, such as azoxystrobin, have been applied as in-furrow and foliar sprays to manage R. solani, but repeated use of QoI fungicides pose risks in fungicide resistance. Penthiopyrad is a novel fungicide with the succinate dehydrogenase inhibitor (SDHI) mode of action. The objectives of this study were to compare the efficacy of penthiopyrad used as a sole seed treatment versus azoxystrobin as an in-furrow or a post-planting application for controlling R. solani; to determine if a penthiopyrad seed treatment combined with azoxystrobin as a post-planting application can improve control of R. solani over sole penthiopyrad seed treatment, azoxystrobin in-furrow or post-planting spray application. Seedling survival rate and area under disease progress curve (AUDPC) for seedling loss rate were used to measure the efficacy of each treatment. A sole penthiopyrad seed treatment at 14 g a. i. kg−1 of seeds, and penthiopyrad seed treatments at 7 and 14 g a. i. kg−1 of seeds combined with one azoxystrobin in-furrow application 14 days after planting resulted in similar seedling survival rate and AUDPC as achieved with the standard azoxystrobin in-furrow application. However, post-planting foliar spray of azoxystrobin alone failed to control seedling damping-off. Our research suggests that penthiopyrad can be used as a seed treatment to provide early protection to vulnerable seedlings while azoxystrobin can be used as a post-planting application to protect the ensuing adult plants.

Sugarbeet roots produced in cold climates are stored in large piles prior to processing and are cooled by ambient winter air. These storage conditions dehydrate roots, causing root respiration rate and sucrose loss in storage to increase. Dehydration likely alters carbohydrate metabolism due to a greater demand for respiratory substrates and may affect the accumulation of non-sucrose carbohydrates that impede processing. However, effects of dehydration on carbohydrate metabolism of postharvest sugarbeet roots have not been studied. Research, therefore, was conducted to determine the effect of mild and severe dehydration on concentrations of the non-sucrose carbohydrates, glucose, fructose, and raffinose, their biosynthetic precursors, and the concentrations of metabolites that are intermediates in respiratory sucrose catabolism through glycolysis and the TCA cycle. Roots were stored at 85 and 40% relative humidity for up to 28 d to generate mildly and severely dehydrated roots typical of roots in the interior and exterior of storage piles. Severe dehydration was associated with reductions in raffinose, galactinol, glucose 6-phosphate, fructose 6-phosphate, phosphoenolpyruvate, and pyruvate concentrations, and increases in inositol and malate concentrations, while mild dehydration was associated with increased raffinose concentration. Concentrations of other glycolytic and TCA cycle intermediates, as well as the invert sugars, glucose and fructose, were largely unaffected by dehydration. From these results, it is concluded that raffinose accumulation and biosynthesis is highly sensitive to root dehydration and that carbohydrate metabolism through glycolysis is altered by dehydration, presumably to provide increased substrates for respiration. Overall, this research provides new insight into the impact of environmental conditions within storage piles on raffinose accumulation and the mechanisms by which dehydration accelerates sucrose loss in stored sugarbeet roots.

Recently, root rots caused by Fusarium spp. have become a major constraint for field pea production in North Dakota. With the inadequate disease management options currently available, this study was initiated to determine whether precipitated calcium carbonate (PCC), a byproduct of the sugar processing industry, could be used for managing fusarium root rots of field pea. The efficiency of PCC in controlling Fusarium species associated with root rots was evaluated in vitro and under greenhouse, and field conditions. Effect of PCC on growth characteristics of six Fusarium spp. viz., F. acuminatum, F. avenaceum, F. redolens, F. solani, F. graminearum, and F. oxysporum, commonly associated with pea root rot was evaluated in vitro. Significant reduction in conidia production, conidial germination, and dry mycelial weight were recorded in presence of PCC in growth media. In the greenhouse, PCC efficacy was tested at varying rates (equivalent to 0, 2.2, 5.6, 11.2, and 22.5 t/ha of field application (corresponding to 0, 1, 2.5, 5 and 10 t/ac, respectively)) in pot culture experiments containing soil infested with F. avenaceum and F. solani, the two most aggressive and common Fusarium pathogens associated with field pea root rots in North Dakota. Significant reduction in root rot disease severity was observed in both F. avenaceum, and F. solani infested pots at all rates of PCC application compared to the controls. Similar results were obtained from multi-location field experiments conducted in 2010 and 2011 with reduction in root rot severity following application of PCC. Results from this study demonstrated that PCC has the potential to serve as a strategy for Fusarium root rot management in field pea.

Rhizoctonia solani Kuhn is an important pathogen of sugar beet ( Beta vulgaris L.) that can cause damping-off and crown and root rot. Commercial cultivars which are highly resistant to the pathogen are not as high yielding as susceptible cultivars under low or absent disease pressure. These resistant cultivars often do not have resistance to other common pathogens such as Aphanomyces cochlioides , Cercospora beticola , and Fusarium oxysporum . Fungicides, such as azoxystrobin which belongs to the quinone outside inhibitors (QoI) class, are necessary for controlling Rhizoctonia solani , but there are concerns about the buildup of fungicide-resistant strains in the targeted pathogen population. There is a need to find effective fungicides from different chemical groups so they can be rotated with the current widely-used azoxystrobin to manage R. solani . The objective of this greenhouse study was to evaluate the efficacy of penthiopyrad, a succinate dehydrogenase inhibitor (SDHI), in managing R. solani on sugar beet using three different application methodologies. Penthiopyrad effectively controlled R. solani on sugar beet when applied at 210, 280, 420, or 550 g a.i./ha in-furrow at planting and as a soil drench at the 4-leaf stage. However, foliar application of penthiopyrad failed to provide disease control. These trials indicated that penthiopyrad needs to be in close proximity or direct contact with R. solani in the soil to provide effective control. Penthiopyrad has the potential to be used as an effective alternate partner with azoxystrobin for controlling R. solani and to help in mitigating the development of fungicide resistant isolates of R. solani .

Rhizoctonia solani is the most serious problem on sugar beet Beta vulgaris L. grown in North Dakota and Minnesota. Picoxystrobin, a quinone outside inhibitor, and penthiopyrad, a succinate dehydrogenase inhibitor, were used alone and in combinations for controlling R. solani AG 2-2 IIIB on sugar beet under greenhouse conditions of 22 ± 2 °C and a 12-h photoperiod. Fungicides were applied in-furrow at planting, followed by inoculation with R. solani grown on barley seeds. The experimental design was a randomized complete block with four replicates and the experiment was repeated three times. Stand counts were taken and roots were evaluated for symptoms using a 0 to 7 scale 21 days after inoculation. Analysis of variance was conducted by the SAS general linear model, and Fisher’s protected least significant difference at α = 0.05 was used to compare treatment means. Fungicides used alone and in mixtures provided effective control of R. solani, which had significantly greater percent survivors than the inoculated check. This research demonstrated that picoxystrobin and penthiopyrad have the potential to be used for providing control of R. solani on sugar beet.

In the past decades, plant disease has been witnessed as the major cause of production and economic losses in the agriculture sector, negatively impacting the ability to feed the world. Vibrational spectroscopy methods such as Infrared and Raman spectroscopy have been used for plant monitoring in agriculture and forestry systems, particularly for disease monitoring. These methods can identify the chemical fingerprints of the physiological interactions caused by diseases in the plants that may not be observed by human eyes. Usually, the latent physiological changes in the plants happen before their presentations on plant phenotypes. Vibrational spectroscopy has been largely successful in lab-scale plant monitoring, whereas the mixed success has been reported in field conditions due to the complex interactions of soil characteristics, environmental conditions, and diseases on plants. In this chapter, we will (1) summarize the applications of vibrational spectroscopy in plant disease detection, (2) introduce how abiotic (plant nutrition deficiency) and biotic factor affect plant health, (3) discuss the relationship between plant disease and vibrational spectroscopic phenomenon, (4) introduce vibrational spectroscopic techniques for plant pathogen detection using feature selection/extraction and machine learning methods.

Cercospora leaf spot (CLS) caused by Cercospora beticola occurs annually in Serbia causing severe yield losses of sugar beet, which requires intensive use of fungicides. In recent years we have observed unsatisfactory control of CLS originating from northwestern Serbia. Frequency of C. beticola populations resistant to Quinone outside inhibitors (QoI) was 81% (51/63 isolates), 98% (62/63) to sterol-demethylation inbibitors (DMI) and 54% (34/63) to methyl-2-benzimidazole carbamate fungicides (MBC). The genetic basis underlying the resistance was tested by characterizing the cob, CYP51 and s-tubulin genes, associated with resistance to QoI, DMI and MBC fungicides, respectively. Isolates that were resistant to QoI fungicides had the G143A mutation in the cob gene. Characterization of the CYP51 gene revealed seven diverse haplotypes; however, no correlation with sensitivity or resistance to DMI fungicides could be identified. Resistance to MBC fungicides was associated with the presence of the E198A mutation in the s-tubulin gene of all resistant isolates. From a total of 63 isolates originating from sugar beet fields of northwestern Serbia, 62 isolates showed resistance to multiple modes of action. Three multi-resistant phenotypes were identified: MR1 (N = 29) - resistant to QoI and DMI fungicides (QoI-R and DMI-R) but sensitive to MBC fungicides (MBC-S); MR2 (N = 11, QoI-S, DMI-R and MBC-R); and MR3 (N = 22), resistant to all three groups of fungicides (QoI-R, DMI-R and MBC-R). This is the first report of C. beticola resistance to QoI fungicides in Serbia. This study revealed development of multi-resistance of C. beticola isolates to MBC, DMI and QoI fungicides, which represents the first record of this phenomenon in C. beticola populations.

This study characterized a novel sugar beet (Beta vulgaris L.) pathogen from the Red River Valley in north central USA, which was formally named Fusarium secorum. Molecular phylogenetic analyses of three loci (translation elongation factor1α, calmodulin, mitochondrial small subunit) and phenotypic data strongly supported the inclusion of F. secorum in the Fusarium fujikuroi species complex (FFSC). Phylogenetic analyses identified F. secorum as a sister taxon of F. acutatum and a member of the African subclade of the FFSC. Fusarium secorum produced circinate hyphae sometimes bearing microconidia and abundant corkscrew-shaped hyphae in culture. To assess mycotoxin production potential, 45 typical secondary metabolites were tested in F. secorum rice cultures, but only beauvericin was produced in detectable amounts by each isolate. Results of pathogenicity experiments revealed that F. secorum isolates are able to induce half- and full-leaf yellowing foliar symptoms and vascular necrosis in roots and petioles of sugar beet. Inoculation with F. acutatum did not result in any disease symptoms. The sugar beet disease caused by F. secorum is named Fusarium yellowing decline. Since Fusarium yellowing decline incidence has been increasing in the Red River Valley, disease management options are discussed.

Rhizoctonia damping-off and crown and root rot of sugar beet caused by Rhizoctonia solani are serious problems in Minnesota and North Dakota. Timely application of azoxystrobin fungicide effectively controls R. solani. Many growers use starter fertilizers at planting as an economic way to apply phosphate and will like to know if mixing azoxystrobin with starter fertilizers is safe and effective. The objective of this research was to determine the efficacy and safety of mixing azoxystrobin with starter fertilizers for controlling R. solani of sugar beet. Research was conducted in a greenhouse maintained at 20 ± 2° C. Three different starter fertilizers 10-34-0, 6-24-6 and Redline were each used at 28.05 L ha-1 and azoxystrobin was used at 167 g a.i. ha-1. Treatments were applied to ten sugar beet seeds planted in a furrow of Sunshine Mix 1 peat filled tray. There were 13 treatments including a non-inoculated and an inoculated control; starter fertilizers used without and with inoculation; azoxystrobin used alone without and with inoculation; and azoxystrobin mixed with each of the different starter fertilizers followed by inoculation. Plants were watered daily and evaluated 28 days after treatments. The non-inoculated control and treatments where only starter fertilizers were used resulted in significantly higher percentages of healthy surviving plants compared to the inoculated control. Azoxystrobin provided similar effective control of R. solani when used alone compared to when it was mixed with starter fertilizers and there was no phytotoxicity. This study suggests that mixtures of azoxystrobin with different starter fertilizers evaluated under greenhouse conditions resulted in no phytotoxicity observed in this study and effectively controlled R. solani.

Dry root rot of chickpea caused by Macrophomina phaseolina is an important disease affecting chickpea production areas in India, the largest producer of this crop in the world. The disease is primarily controlled through the use of fungicidal seed treatments. In this study, several isolates of two bio-control agents, Trichoderma viride and Pseudomonas fluorescens, were assessed for their ability to reduce the growth of M. phaseolina under laboratory conditions and subsequently used for field studies. The most effective isolate of each bio-control agent and the commonly used chemical seed-treatments, carbendazim and hexaconazole were evaluated. In addition to the use of the fungicides and bio-control agents individually as seed treatments, the study also included a trial combining soil application through bio-agent enriched farm-yard manure, along with seed treated with the bio-control agent. It was found that this combination showed maximum germination, least root rot incidence and highest yields as compared to the other biological or chemical seed treatments included in this study. This paper reports the identification of native isolates of T. viride and P. fluorescens that can be used under field conditions to control dry root rot of chickpea in tropical regions and demonstrates the use of a method of application that could significantly improve the efficacy of disease control while using bio-control agents.

In Minnesota and North Dakota, Cercospora leaf spot (CLS), caused by the fungus Cercospora beticola Sacc., is the most damaging foliar disease of sugar beet (Beta vulgaris L.). Fungicide applications are necessary under moderate to severe disease pressure to control CLS to obtain economically viable yields of recoverable sucrose. Field trials were conducted near Foxhome, Minnesota in 2005 and 2006 to determine whether the broad-spectrum herbicide glyphosate applied post inoculation to glyphosate-resistant sugar beet controls C. beticola and improves crop yield and quality compared to using fungicides. The research site was artificially inoculated with C. beticola and multiple applications of glyphosate were applied alongside the fungicides tetraconazole, pyraclostrobin, and triphenyltin hydroxide used in rotation. CLS disease severity was high in both years as measured by the area under the disease progress curve (AUDPC). Glyphosate applied post inoculation at the same time as parallel applications of fungicides were performed did not provide effective control of CLS and resulted in similar AUDPC, yield and quality as the non-treated check. Fungicides provided effective control of C. beticola with lower AUDPC and resulted in significantly higher yields and recoverable sucrose than the non-treated check. Additional

Cercospora leaf spot (CLS), caused by the fungus Cercospora beticola, is the most economically important foliar disease of sugar beets in Italy. It can be controlled with the integrated use of resistant varieties, crop practices and foliar fungicides. Environmental conditions strongly influence the activity of C. beticola in the field; they can be used to guide fungicide applications once the relationships are understood. To assist growers in application of foliar fungicides for CLS control, a predictive model, developed at the University of Minnesota and North Dakota State Universities, was evaluated under Italian conditions. The model was designed to predict the time when the infection by C. beticola was initiated based on hourly temperature and relative humidity data. CLS control is currently based on treatments scheduled using a ‘‘calendar’’ programme. This system recommends to start fungicide applications on a fixed date and continue regularly every 18–20 days. Three years of field trial evaluation of the CLS prediction model at several experimental sites, compared with the calendar programme, has resulted in a savings of 1.5 fungicide treatments (corresponding to 130 €/ha) without a significant loss of yield. To control CLS, multiple applications of the same fungicide during a growing season are unfortunately common. This practice provides the target fungus a suitable condition to evolve resistance. Sensitivity assays of C. beticola to DMI and QoI fungicides were carried out on CLS isolates collected in 2009 and 2010 in Northern Italy by the University of Bologna and North Dakota State University, respectively. CLS isolates were tested sensitivity to tetraconazole, difenoconazole, pyraclostrobin and trifloxystrobin using radial growth and spore germination assays. All samples collected in 2009 showed EC50 values for QoI ranging from 0.0008 to 0.2195 lg/ml. The percentage of isolates collected in 2010 with EC50 values [1 for tetraconazole was 44 %, for difenoconazole 84 %, for pyraclostrobin 27 % and for trifloxystrobin 34 %. For isolates with EC50 values [1 lg/ml, the range of EC50 values (lg/ml) for tetraconazole was 3.4–70.0, for difenoconazole 2.0–69.5, for pyraclostrobin 1.5–43.6, and for trifloxystrobin 3.8–77.1, respectively.

In all, 98 isolates of three Fusarium spp. (18 Fusarium oxysporum, 30 F. graminearum, and 50 Fusarium sp. nov.) obtained from sugar beet in Minnesota were characterized for pathogenicity and virulence on sugar beet in the greenhouse by a bare-root inoculation method. Among the 98 isolates tested, 80% of isolates were pathogenic: 83% of the F. oxysporum isolates, 57% of the F. graminearum isolates, and 92% of the Fusarium sp. nov. isolates. Symptoms varied from slight to moderate wilting of the foliage, interveinal chlorosis and necrosis, and vascular discoloration of the taproot without any external root symptoms. Among the pathogenic isolates, 14% were highly virulent and 12% were moderately virulent. Most of the highly virulent isolates (91%) and moderately virulent isolates (89%) were Fusarium sp. nov. All pathogenic isolates of F. graminearum and most pathogenic isolates (87%) of F. oxysporum were less virulent. In general, more-virulent isolates induced first foliar symptoms earlier compared with less-virulent isolates. This study indicates that both F. oxysporum and Fusarium sp. nov. should be used in greenhouse and be present in field studies used for screening and developing sugar beet cultivars resistant to Fusarium yellows complex for Minnesota and North Dakota.

Cercospora leaf spot (CLS), caused by the fungal pathogen Cercospora beticola, is the most important foliar disease of sugar beet worldwide. Control strategies for CLS rely heavily on quinone outside inhibitor (QOI) fungicides. Despite the dependence on QOIs for disease control for more than a decade, a comprehensive survey of QOI sensitivity has not occurred in the sugar beet growing regions of France or Italy. In 2010, we collected 866 C. beticola isolates from sugar beet growing regions in France and Italy and assessed their sensitivity to the QOI fungicide pyraclostrobin using a spore germination assay. In total, 213 isolates were identified with EC50 values greater than 1.0 μg ml−1 to pyraclostrobin, all of which originated from Italy. To gain an understanding of the molecular basis of QOI resistance, we cloned the full-length coding region of Cbcytb, which encodes the mitochondrial QOI-target enzyme cytochrome b in C. beticola. Cbcytb is a 1,162-bp intron-free gene with obvious homology to other fungal cytb genes. Sequence analysis of Cbcytb was carried out in 32 QOI-sensitive ( 1.0 μg ml−1) isolates. All tested QOI-resistant isolates harboured a point mutation in Cbcytb at nucleotide position 428 that conferred an exchange from glycine to alanine at amino acid position 143 (G143A). A PCR assay developed to discriminate QOI-sensitive and QOI-resistant isolates based on the G143A mutation could detect and differentiate isolates down to approximately 25 pg of template DNA. Microsatellite analyses suggested that QOI resistance emerged independently in multiple genotypic backgrounds at multiple locations. Our results indicate that QOI resistance has developed in some C. beticola populations in Italy and monitoring the G143A mutation is essential for fungicide resistance management in this pathosystem.

Baseline sensitivity was determined using in vitro radial growth assay for Fusarium oxysporum, Fusarium graminearum, and a novel uncharacterized Fusarium sp. nov. from sugarbeet, and F. sambucinum from potato, to metconazole, triticonazole, and thiabendazole. All the isolates from sugarbeet and a thiabendazole-sensitive F. sambucinum isolate were sensitive to the tested fungicides. A thiabendazole-resistant isolate of F. sambucinum was resistant to thiabendazole but sensitive to the other two fungicides. The EC50 values of F. oxysporum, F. graminearum, and F. sp. nov. for triticonazole were 0.51 μg ml-1, 2.15 μg ml-1, and 0.04 μg ml-1, respectively. The EC50 values of F. oxysporum, F. graminearum, and F. sp. nov. for metconazole were 0.04 μg ml-1, 0.03 μg ml-1, and 0.02 μg ml-1, respectively. The EC50 values of F. oxysporum, F. graminearum, and F. sp. nov. for thiabendazole were 0.57 μg ml-1, 0.54 μg ml-1, and 0.64 μg ml-1, respectively. Generally, a higher concentration of triticonazole and thiabendazole compared to metconazole were required to reduce colony growth by 50%. The low EC50 values of metconazole, triticonazole, and thiabendazole for the Fusarium species tested suggest that they are potential candidates for control of Fusarium diseases of sugarbeet. Research is needed to determine the 24 Journal of Sugar Beet Research Vol. 47 Nos. 1 & 2 effectiveness of these fungicides for control of Fusarium diseases under field conditions. Additional key words: Beta vulgaris, benzimidazole, EC50, triazole. M and North Dakota ranked first and second in sugarbeet production in the United States during 2008 (USDA ERS, 2009). The acreage planted in the bi-state area was 312,417 ha, that represented 58% of the total United States crop. The fungal diseases, Cercospora leaf spot, Aphanomyces root rot, and Rhizoctonia crown and root rot, are the most damaging diseases for the sugarbeet industry in this region. In 2002, another fungal disease, Fusarium yellows, was reported in Minnesota and North Dakota (Khan et al., 2003). Fusarium yellows is becoming a serious problem particularly for growers in the Moorhead factory district (Windels et al., 2005). Pathogenicity studies (Burlakoti, 2007) confirmed that F. oxysporum, F. graminearum, and novel, previously undescribed Fusarium species, hereafter referred to as F. sp. nov (Rivera et al., 2008) recovered from diseased sugarbeet with foliar symptoms similar to Fusarium yellows, from fields in west-central Minnesota (Sabin, Fossum, and Georgetown), caused foliar yellowing and vascular discoloration of sugarbeet seedlings in greenhouse conditions. Fusarium diseases of sugarbeet have been reported from Nebraska (Bockstahler, 1940), Wyoming and Minnesota (Hanson, 2006a), Michigan (Hanson, 2006b), Colorado (Hanson and Jacobsen, 2006; Stewart, 1931), Texas, (Harveson and Rush, 1997; Ruppel, 1991; Rush and Martyn, 1991), Oregon (Rush and Martyn, 1991), North Dakota and Minnesota (Windels et al., 2005; Khan et al., 2003), India, Belgium, Germany, and the Netherlands (Duffus and Ruppel, 1993). Fusarium diseases on sugarbeet causes yield loss due to poor plant population, stunted growth, and increased impurities in extracted juice (Bosch and Mirocha, 1992; Harveson and Rush, 1997; Schneider and Whitney, 1986; Windels et al., 2005). The use of resistant cultivars is an effective means to manage many diseases of sugarbeet (Biancardi, 2005; Bugbee and Cole, 1979). Screening for cultivars resistant to Fusarium diseases in Minnesota and North Dakota started in 2005 (Niehaus, 2006). Effective host-plant resistance to Fusarium diseases of sugarbeet have not been identified (Francis and Luterbacher, 2003). No commercial sugarbeet cultivar is immune to Fusarium diseases and most cultivars have at least some susceptibility (Biancardi, 2005). In this context, fungicides should be considered as a tactic to control the disease. Currently, triazole fungicides provide the most effective control Jan. July 2010 Baseline Sensitivity 25 of Fusarium species (Mesterhazy et al., 2003). Triazoles have provided control of Fusarium head blight of small grains, dollar spot and other diseases of turfgrass in the United States for many years (Koller, 1988; Loss et al., 2005). Haidukowski et al. (2005) reported that efficacy of triazole fungicides at controlling Fusarium head blight depended upon the time of application and control ranged from 25% to 89% in field conditions. Thiabendazole belongs to the benzimidazole class of fungicide. Thiabendazole binds the beta tubulin gene and inhibits fungal growth (Davidse, 1986). Benzimidazole has provided control of Fusarium species on seedlings, and tubers of a variety of crops (Davidse, 1986; Hanson et al., 1996). For example, soil drenching by benomyl reduced foliar and internal xylem-browning symptoms of Fusarium wilt of tomato caused by F. oxysporum f. sp. lycopersici (Erwin, 1973). Thiabendazole provided effective control against Fusarium wilt in potato caused by several Fusarium species (Secor et al., 1992). However, prolonged usage of thiabendazole resulted in resistance to thiabendazole in some isolates of F. sambucinum, F. solani, F. oxysporum, F. acuminatum, and F. culmorum from potato (Hanson et al., 1996). In vitro sensitivity of Fusarium species associated with sugarbeet to the triazoles, metconazole and triticonazole, and thiabendazole have not been determined. It would be useful to determine sensitivity of Fusarium species associated with Fusarium diseases of sugarbeet to triazoles and thiabendazole to evaluate their potential for field use. The objective of this study was to determine the baseline sensitivity of F. oxysporum, F. graminearum, and F. sp. nov. (Rivera et al., 2008) associated with sugarbeet in Minnesota and North Dakota to metconazole, triticonazole, and thiabendazole. MATERIALS AND METHODS Isolate collection and growing condition. Ninety-eight isolates [50 Fusarium sp. nov., 18 Fusarium oxysporum, and 30 Fusarium graminearum] were collected in Minnesota from Fusarium-diseased sugarbeet in 2005, and twenty five Fusarium oxysporum isolates were collected in 2006. A thiabendazole-resistant isolate (420-1c) and thiabendazole-sensitive (413-1a) isolate of Fusarium sambucinum from potato was used as a check in the thiabendazole-sensitivity in-vitro assay and also was grown on metconazole and triticonazole amended plates as described by Estrada (2007). Each isolate was transferred to two petri dishes containing freshly prepared half strength potato dextrose agar (HPDA) and incubated at 25 to 26°C for five days under 24 h fluorescent light. HPDA was prepared by autoclaving 100 26 Journal of Sugar Beet Research Vol. 47 Nos. 1 & 2 g of potato in 1 liter of distilled water for 20 min. followed by straining through cheesecloth to remove the water. The potato extract was mixed with 10 g dextrose and 10 g agar and autoclaved for 20 min. Fungicide sensitivity in vitro assay. The sensitivity of each isolate to thiabendazole (technical grade, Merck and Co., Rahway, NJ), metconazole, and triticonazole (commercial, BASF, Raleigh, NC) was determined by comparing the radial growth of each isolate on fungicide amended media to growth on nonamended media. Thiabendazole was dissolved in dimethyl sulfoxide (DMSO) due to greater solubility and to control bacterial growth (Kawchuk et al., 1994). Metconazole and triticonazole were dissolved in sterile distilled water to obtain stock solution of 100μg mL-1 which was further diluted to 10, 1, 0.1, and 0.01μg mL-1. Each concentration of each fungicide was incorporated into autoclaved media. The effect of the fungicide on mycelial growth in vitro was determined on HPDA media amended with 0, 0.01, 0.1, 1, 10, and 100 μg mL-1 of fungicide. A 5-mm diameter mycelial plug from the margin of a five day old actively growing culture of each isolate was inverted and transferred to the center of petri dishes (90 mm) with the fungicide amended media and the non-amended media. Isolate sensitivity to fungicides was assessed by measuring colony diameter of mycelial growth after 6 days of incubation at room temperature in the dark for F. graminearum and after seven days of incubation for F. oxysporum and F. sp. nov. Two perpendicular measurements of colony diameter, excluding the original plug diameter (5 mm), were obtained from each plate. Isolates were replicated twice with two plates per replication at each fungicide concentration. The experiment was repeated. The diameter of each colony on fungicide amended medium relative to the diameter of the colony on non-amended medium was recorded. The relative growth reduction percentage for each fungicide concentration was calculated as follows; [100-(diameter on fungicide amended medium/diameter on nonamended medium)*100]. EC50 values of each isolate were calculated by determining the effective fungicide concentration that inhibited mycelial growth by 50%. We considered isolates as sensitive if their EC50 values were equal to or less than 10 μg ml-1, and resistant if their EC50 values were greater than 10 μg ml-1 (Kawchuk et al. 1994). Data analysis. The effective fungicide dose that inhibited radial growth by 50% (EC50) was determined for each isolate by using the general linear modeling procedure in Statistical Analysis System (SAS Institute, Cary, Jan. July 2010 Baseline Sensitivity 27 NC). A homogeneous test was conducted for the repeated experiments based on calculated F values and Bartlett chi-square values before combining the data from the repeated experiment.

Cercospora leaf spot, caused by Cercospora beticola, is the most damaging foliar disease of sugar beet in Minnesota (MN) and North Dakota (ND). Research was conducted to characterize the temporal progression of aerial concentration of C. beticola conidia in association with the environment and disease severity in sugar beet. In 2003 and 2004, volumetric spore traps were placed within inoculated sugar beet plots to determine daily dispersal of conidia at Breckenridge, MN, and St. Thomas, ND. Plots were rated weekly for disease severity. At both locations, conidia were first collected in early July 2003 and late June in 2004. Peaks of conidia per cubic meter of air were observed with maxima in late August 2003 and in early September 2004 at both locations. Peaks of airborne conidium concentration were significantly correlated with the average temperature of daily hours when relative humidity was greater than 87%. Weekly mean hourly conidia per cubic meter of air was significantly (P < 0.01) associated with disease severity during both years and across locations. This study showed that C. beticola conidial numbers may be used to estimate potential disease severity that, with further research, could be incorporated in a disease forecasting model to rationalize Cercospora leaf spot management.

Cercospora beticola survives as stromata in infected crop residue. Spores produced on these survival structures serve as primary inoculum during the next cropping season. This study was conducted to determine how long C. beticola can survive at different soil depths, the mechanism of inoculum dispersal, and the primary infection site in sugar beet. Longevity of C. beticola was studied over a 3-year period under field conditions at Fargo, ND. C. beticola-infected leaves were placed at depths of 0, 10, and 20 cm and retrieved after 10, 22, and 34 months. Survival of C. beticola inoculum declined with time and soil depth. Inoculum left on the soil surface, 0 cm in depth, survived the longest (22 months) compared with that buried at 10 cm (10 months) and 20 cm (10 months). C. beticola dispersal from the primary source of inoculum was studied in the field for three growing seasons. Sugar beet plants were surrounded with plastic cages with and without ground cover, or exposed with and without ground cover. Significantly higher disease severity was observed on exposed plants than caged plants with or without ground cover, suggesting that wind was the major dispersal factor for C. beticola inoculum. The primary infection site by C. beticola was determined in a greenhouse study. Leaves, roots, and stems of healthy sugar beet plants were inoculated with C. beticola. Cercospora leaf spot symptoms were observed only on plants that were leaf inoculated, suggesting that the leaf was the primary infection site for C. beticola.

Management of Cercospora leaf spot, caused by Cercospora beticola, is necessary for the economic production of sugar beet (Beta vulgaris). The objectives of this study were to evaluate the impact of two relative humidity thresholds (87 and 90%) on the daily infection values (DIVs) used to determine when fungicide applications were required, to determine whether current Cercospora management recommendations for northern areas of Minnesota and North Dakota could be used by growers in the southern areas of these states, and to compare the utility of calendar-based fungicide applications with the Cercospora management model. Research was conducted in Breckenridge, MN and St. Thomas, ND in 2003 and 2004. Fungicide applications significantly (P = 0.05) reduced maximum disease severity (ymax) and area under the disease progress curve (AUDPC) when compared with the nontreated control at both locations during 2003 and 2004. Fungicides applied according to DIVs calculated at RH ≥ 87% or RH > 90% gave similar results. The mandatory second fungicide application 14 days after the first application for southern areas did not significantly decrease disease severity or AUDPC, or improve root yield or recoverable sucrose compared with treatments without the mandatory application. This research illustrates that a DIV calculated at RH ≥ 87% would result in similar timing of fungicide applications compared with DIVs calculated at RH > 90%. The results further show that the recommendation of fungicide applications at initial symptom and subsequent applications based on DIV and disease severity should be used for both northern and southern growers. Finally, this research showed that fungicide applications based on the Cercospora management model provided similar, effective disease control with fewer fungicide applications compared with calendar-based applications.