Postharvest diseases cause significant sucrose losses in sugarbeet during storage, which is estimated at millions of tons each year. Numerous pathogens can cause sugarbeet postharvest disease problems. No effective control measures are currently available to minimize sugar loss caused by the storage diseases in sugarbeet. Low concentrations of chlorine dioxide (ClO2) were used in a closed system to test whether the gas can reduce or eliminate sugarbeet storage pathogens. Penicillium vulpinum spores exposed to 0.005 or 0.01 g L- 1 ClO2 gas for 1 h significantly reduced conidial germination, whereas exposure to 0.02 or 0.04 g L- 1 ClO2 gas eliminated nearly 100 % of conidial viability within 1 h. In storage experiments, ClO2 application also reduced pathogen growth and the associated tissue damage during sugarbeet storage up to seven weeks. Storage pathogens, including Penicillium spp., Pichia membranifaciens, and Leuconostoc suionicum, were eliminated from ClO2 treated sugarbeet roots. Sucrose retention was numerically higher in ClO2-treated roots than controls but was not statistically different. Importantly, the formation of invert sugars, impurities that impede the sucrose extraction process, decreased with ClO2 treatments as low as 0.025 g kg- 1 of sugarbeet roots compared to non-treated controls. In addition, raffinose content was reduced by treatment with 0.05 and 0.1 g of ClO2 kg- 1 of sugarbeet root. Our findings suggest that ClO2 treatment might be effective to mitigate storage diseases and sucrose catabolism in stored sugarbeet. This pilot study, conducted in a controlled environment, provides baseline data for planning larger-scale experiments simulating commercial storage conditions.

Sugarbeet roots are severely wounded during harvest, triggering wound-healing responses to seal off and defend damaged cells. Primary carbon metabolism is required to provide metabolic energy and substrates for wound healing processes, yet how wounding alters primary carbon metabolism is largely unstudied in sugarbeet or other plant species. Wound effects on primary carbon metabolism were determined in the 24 h following injury by evaluating changes in gene expression and enzymatic activities of primary carbon metabolic pathways. Wounding significantly altered expression of 43 primary carbon metabolic pathway genes including 3, 19, 3, 7, and 9 genes involved in sucrolysis, glycolysis, TCA cycle/organic acid metabolism, pentose phosphate pathway, and fermentation, respectively. Highly upregulated genes were involved in sucrolysis, glycolysis, and fermentation, although only enzymatic activities of glycolytic and fermentative enzymes were majorly increased. The results indicate that wounding rapidly upregulates glycolysis and fermentation, with minimal effect on sucrolysis, the TCA cycle and the pentose phosphate pathway. We propose that glycolysis has a dominant role in controlling and upregulating carbon metabolism to support wound healing in postharvest sugarbeet roots, independent of elevations in sucrose catabolism or the TCA cycle, and fermentation is intensely upregulated to maintain glycolytic flux due to the insufficient activity of the TCA cycle to metabolize glycolytic end-products.

BACKGROUND:Ethanol is a common contaminant in sugarbeet factories that is believed to be produced by fermentation of sucrose by microbes present in the factory. Ethanol, however, may also enter factory processing streams as a contaminant in delivered sugarbeet roots, although no studies have examined whether harvested and stored roots contain ethanol or evaluated factors that might affect ethanol accumulation in postharvest roots. Research was conducted to determine the capability and extent to which sugarbeet roots produce and accumulate ethanol following harvest and determine the effects of storage temperature, duration, ventilation, and rots on root ethanol concentration. RESULTS:Harvested and stored sugarbeet roots contained the gene transcripts and enzymatic activities required for fermentation and accumulated ethanol at concentrations of 300 to 900 ppm. Root ethanol concentrations were unaffected by storage temperature or duration during 90 days storage at 5, 12, or 20 °C and were unaffected by reductions in root ventilation that lowered oxygen concentrations by 32%. However, the fungal pathogens, Botrytis cinerea and Penicillium vulpinum, and the opportunistic bacterium, Leuconostoc suionicum, significantly increased ethanol concentration in rotted root tissues. CONCLUSION:Sugarbeet roots delivered to factories contain ethanol and contribute to ethanol in factory processing streams. Results indicate that healthy roots constitutively produce ethanol at low levels and that storage diseases significantly elevate root ethanol concentrations. Efforts to reduce postharvest sucrose loss due to fermentation, therefore, should consider not only fermentation by microbes in the factory, but also fermentation within harvested and stored roots. Published 2025. This article is a U.S. Government work and is in the public domain in the USA.

ABSTRACTSugarbeets are largely produced without irrigation, making drought stress inevitable when rainfall is insufficient. Whether drought stress impacts root storage, however, is currently unknown. Research was conducted to determine the effect of preharvest water stress on postharvest sugarbeet root respiration rate and susceptibility to storage rots as these traits are the primary determinants for sucrose loss and quality deterioration. Greenhouse‐grown plants were subjected to four levels of water deficit by discontinuing watering for 0, 7, 14 or 21 days prior to harvest. Plants receiving water‐restrictive treatments displayed physiological stress by leaf epinasty, reductions in net photosynthetic rate and leaf relative water content and increases in leaf temperature, whereas the water content of roots harvested from these plants progressively decreased with the severity of the preharvest water‐deficit treatment. Harvested roots from all watering treatments were stored at 10°C and 95% relative humidity for up to 12 weeks and evaluated for respiration rate and susceptibility to storage rot. Root respiration rate during storage was inversely related to root water content at harvest by second‐order equations, such that respiration was not significantly affected by minor reductions in root water content but increased exponentially for roots obtained from severely drought‐stressed plants with water contents at harvest of ≤75%. Similarly, roots with water contents ≤75% had elevated levels of electrolyte leakage, a measure of cellular membrane damage, and were more susceptible to dehydration and fungal infection during storage. In separate experiments, roots harvested from water‐stressed plants were inoculated with Botrytis cinerea or Penicillium vulpinum, two causal agents for storage rots. In these experiments, preharvest water stress quantitatively increased root rot and qualitatively altered symptoms of their infection. Overall, these results demonstrate that severe preharvest drought stress is likely to significantly increase sugarbeet root storage losses caused by root respiration and storage rots and that storage losses are likely to accelerate with time in storage. However, mild‐to‐moderate drought conditions prior to harvest are expected to have no or minimal effect on storage losses from root respiration or storage rots.

Endogenous metabolism is primarily responsible for losses in sucrose content and processing quality in postharvest sugarbeet roots. The genes responsible for this metabolism and the transcriptional changes that regulate it, however, are largely unknown. To identify genes and metabolic pathways that participate in postharvest sugarbeet root metabolism and the transcriptional changes that contribute to their regulation, transcriptomic and metabolomic profiles were generated for sugarbeet roots at harvest and after 12, 40 and 120 d storage at 5 and 12°C and gene expression and metabolite concentration changes related to storage duration or temperature were identified. During storage, 8656 genes, or 34% of all expressed genes, and 225 metabolites, equivalent to 59% of detected metabolites, were altered in expression or concentration, indicating extensive transcriptional and metabolic changes in stored roots. These genes and metabolites contributed to a wide range of cellular and molecular functions, with carbohydrate metabolism being the function to which the greatest number of genes and metabolites classified. Because respiration has a central role in postharvest metabolism and is largely responsible for sucrose loss in sugarbeet roots, genes and metabolites involved in and correlated to respiration were identified. Seventy-five genes participating in respiration were differentially expressed during storage, including two bidirectional sugar transporter SWEET17 genes that highly correlated with respiration rate. Weighted gene co-expression network analysis identified 1896 additional genes that positively correlated with respiration rate and predicted a pyruvate kinase gene to be a central regulator or biomarker for respiration rate. Overall, these results reveal the extensive and diverse physiological and metabolic changes that occur in stored sugarbeet roots and identify genes with potential roles as regulators or biomarkers for respiratory sucrose loss.

Abstract Storage rots are a significant cause of postharvest losses for the sugar beet crop, however, intrinsic physiological and genetic factors that determine the susceptibility of roots to pathogen infection and disease development are unknown. Research, therefore, was carried out to evaluate the disease development in sugar beet roots caused by two common storage pathogens as a function of storage duration and storage temperature, and to identify changes in the expression of defense genes that may be influencing the root susceptibility to disease. To evaluate root susceptibility to disease, freshly harvested roots were inoculated with Botrytis cinerea or Penicillium vulpinum on the day of harvest or after 12, 40, or 120 d storage at 5 or 12 °C and the weight of rotted tissue present in the roots after incubation for 35 d after inoculation were determined. Disease susceptibility and progression to B. cinerea and P. vulpinum increased with storage duration with elevations in susceptibility occurring more rapidly to B. cinerea than P. vulpinum. Also, B. cinerea was more aggressive than P. vulpinum and caused greater rotting and tissue damage in postharvest sugar beet roots. Storage temperature had minimal effect on root susceptibility to these rot-causing pathogens. Changes in defense gene expression were determined by sequencing mRNA isolated from uninoculated roots that were similarly stored for 12, 40 or 120 d at 5 or 12 °C. As susceptibility to rot increased during storage, concurrent changes in defense-related gene expression were identified, including the differential expression of 425 pathogen receptor and 275 phytohormone signal transduction pathway-related genes. Furthermore, plant resistance and hormonal signaling genes that were significantly altered in expression coincident with the change in root susceptibility to storage rots were identified. Further investigation into the function of these genes may ultimately elucidate methods by which storage rot resistance in sugar beet roots may be improved in the future.

Bacterial contamination of raw diffusion juice poses unique challenges during the sugar extraction process. This study profiled bacterial communities by using full-length 16S rRNA amplicon sequencing and quantified the carbohydrate concentrations in raw diffusion juice samples received from sugar factory regions across the USA and Canada. Juice samples were collected at four time points during the 2021 and 2022 processing campaigns. Firmicutes was the dominant phylum from the raw diffusion juice samples collected during both campaigns and comprised 85.5% of total bacterial abundance. Lactic acid bacteria such as Leuconostoc and Lactobacillus were among the core genera which also dominated the bacterial community in raw diffusion juice. Positive correlations in the abundance of functionally and taxonomically related bacterial communities were identified. During the 2021 campaign, 44 bacterial genera were differentially abundant in raw diffusion juice extracted from sugarbeet roots in Periods 1 to 4. This number declined sixfold during the 2022 campaign to three genera. The concentration of raffinose in raw diffusion juice positively correlated to the relative abundance of Leuconostoc. Furthermore, an in vitro assay was performed to assess the growth dynamics of Leuconostoc mesenteroides in sucrose or raffinose-rich medium and observed the rapid consumption of both carbohydrates by this bacterium. This finding is important for deciphering microbial growth dynamics in raw diffusion juice that can be useful in minimizing sugar loss during the factory processing.IMPORTANCEFindings additionally provide baseline information that can be used to develop mitigation strategies that reduce losses due to microbial contamination of sucrose processing streams.

Cercospora leaf spot (CLS; causal agent Cercospora beticola Sacc.) is endemic in many sugar beet production regions due to the widespread distribution of C. beticola and the inability of current management practices to provide complete control of the disease. Roots harvested from plants with CLS, therefore, are inevitably incorporated into sugar beet root storage piles, even though the effects of CLS on root storage properties are largely unknown. Research was conducted to determine the effects of CLS on storage properties including root respiration rate, sucrose loss, invert sugar accumulation, loss in recoverable sucrose yield, and changes in sucrose loss to molasses with respect to CLS disease severity and storage duration. Roots were obtained from plants with four levels of CLS severity in each of three production years, stored at 5°C and 95% relative humidity for up to 120 days, and evaluated for storage characteristics after 30, 90, and 120 days storage. No significant or repeatable effects of CLS on root respiration rate, sucrose loss, invert sugar accumulation, loss in recoverable sucrose yield, or change in sucrose loss to molasses were detected after 30, 90, or 120 days storage regardless of the severity of CLS disease symptoms. Therefore, no evidence was found that CLS accelerates sugar beet storage losses, and it is concluded that roots harvested from plants with CLS can be stored without additional or specialized precaution, regardless of CLS symptom severity.

Respiration is the principal cause for postharvest sucrose loss in sugarbeet (Beta vulgaris L.) roots. Although reductions in respiration rate could mitigate these losses, developing sugarbeet cultivars and storage procedures that reduce respiration are hindered by a lack of knowledge of the genetic and metabolic factors that control storage respiration rate. Research was conducted to identify genes and gene products that affect storage respiration rate by creating two sugarbeet lines that differ in respiration rate and characterizing gene expression differences between these lines. Sugarbeet lines F1056 and F1057, which differ by up to 42% in respiration rate, were created by divergent selection of a sugarbeet population using root respiration rate after 30 d in storage as the principal selection criterion. RNA sequencing identified 287 differentially expressed genes (DEGs) between these lines on the day of harvest and after 28-d storage. Of these DEGs, nine encoded transcription factors and five encoded enzymes involved in the respiratory pathway. Other DEGs contributed to a variety of biological and molecular functions based on gene ontology classifications. Of respiratory pathway DEGS, genes for NAD(+)- and NADP(+)-dependent forms of glyceraldehyde-3-phosphate dehydrogenase were of note due to their high upregulation in the high respiring line and for their established role in glycolysis, a pathway identified as a likely bottleneck in respiratory substrate production. Overall, lines F1056 and F1057 provide new tools for investigating genetic and physiological differences in storage respiration rate, and their DEGs identify candidates for genes affecting sugarbeet root respiration rate.

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.

Sucrose metabolism is believed to have a central role in promoting sink strength and sucrose storage in the sugarbeet taproot. How sucrose accumulation is increased by sucrose-degrading enzymes, however, is a paradox. To elucidate roles for sucrose-degrading activities in sucrose accumulation, relationships between the inter-cellular location of sucrose-catabolizing enzymes and sites of sucrose accumulation were determined in the sugarbeet taproot. Sucrose storage was evident in parenchyma cells of the outer cortex, rays, and rings of parenchyma tissue, but was absent in phloem, the vascular cambium, cells surrounding these tissues, or cells surrounding xylem. Sucrose synthase, which was primarily responsible for sucrose catabolism throughout the taproot, was expressed in similar cell and tissue types to those accumulating sucrose. Colocalization of sucrose synthase with sucrose accumulation, as well as sucrose synthase localization near the tonoplast, suggests a role for the enzyme in generating metabolic energy to fuel sucrose sequestration in the vacuole. Localization near the plasma membrane also suggests a role for sucrose synthase in supplying substrates for cell wall biosynthesis. By utilizing sucrose for ATP or cell wall biosynthesis, sucrose synthase likely maintains the source-to-sink sucrose gradient that drives sucrose transport into the root, thereby promoting sugarbeet root sink strength.

Drought is the major cause of yield and economic loss for the sugar beet crop. Mechanisms to reduce drought stress, however, are lacking as sugar beets are largely produced without irrigation and drought-tolerant varieties are not available. As jasmonates are implicated in plant drought-stress responses, research was conducted to determine whether methyl jasmonate (MeJA) could mitigate drought effects on sugar beet. Fourteen-day-old plants were treated with 0, 0.01, 0.1, 1 or 10 mu M MeJA. Seven days later, half of the plants were drought-stressed by withholding water, while control plants continued to receive water. Drought caused leaf relative water content (RWC), shoot fresh and dry weights, net photosynthetic rate (Pn), transpiration rate (EVAP), stomatal conductance (Gs), water-use efficiency (WUE) and PSII quantum efficiency to decline and substomatal CO2 concentration (Ci) and proline and betaine concentrations to increase. MeJA, at 1 and 10 mu M, reduced moderate and severe drought effects on RWC, Pn, Ci and WUE and altered drought-induced changes in proline accumulation, but had no effect on Gs, EVAP or betaine accumulation. Results indicate that MeJA delayed plant dehydration and protected the photosynthetic apparatus from drought-induced impairment. Exogenous application of MeJA, therefore, alleviates drought stress on young sugar beets and may provide a tool to reduce the economic loss caused by dry conditions during early crop production.

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The fungus, Metarhizium anisopliae (Metschnikoff) Sorokin, has potential as an alternative to chemical soil insecticides for the management of the sugarbeet root maggot. For 3 years (1996-98) in the same field, soil applications of an isolate of the fungus (ARS-T1) were in a rotation of wheat, barley, and sugarbeets and seasons (fall and spring) to evaluate the effectiveness of management strategies. There is a need to better understand what happens to the fungus in the soil after applications (i.e., what concentration of conidia is present, do conidia persist throughout the season, does the fungal concentration build up with repeated applications or timing of applications, and do conidia move within the soil profile?). From May 27 to Aug 19 of 1998, soil samples within the top 22.5 cm (in increments of 7.5 cm) of the soil profile were taken every 2 weeks and analyzed for the presence and quantity of conidia. Concentrations of conidia for the fungal treatments ranged from approximate to 4.0 x 10(4)-1.6 x 10(5) CFU/g of soil throughout the sampling period. The number of conidia did not increase with more applications, nor did timing of applications (fall vs, spring) affect the levels of conidia present in the soil. 57-89% of the conidia was present in the top 7.5 cm of the soil profile, and there were significantly fewer conidia present in the middle and bottom 7.5 cm of the soil profile when applications were made for only 2 years. The data suggest the fungus persists overwinter and during the period of maggot activity with no appreciable reduction in conidial concentration, there is minimal buildup of inoculum over the years or with timing of applications, and there is more downward movement of conidia with more years of applications.