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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., (© 2024. This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply.)

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., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2024 Fugate, Eide, Lafta, Tehseen, Chu, Khan and Finger.)

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., Competing Interests: The author(s) declare no conflict of interest.

Injuries sustained by sugarbeet ( Beta vulgaris L.) roots during harvest and postharvest operations seriously reduce the yield of white sugar produced from stored roots. Although wound healing is critically important to reduce losses, knowledge of these processes is limited for this crop as well as for roots in other species. To better understand the metabolic signals and changes that occur in wounded roots, dynamic changes in gene expression were determined by RNA sequencing and the activity of products from key genes identified in this analysis were determined in the 0.25 to 24 h following injury. Nearly five thousand differentially expressed genes that contribute to a wide range of cellular and molecular functions were identified in wounded roots. Highly upregulated genes included transcription factor genes, as well as genes involved in ethylene and jasmonic acid (JA) biosynthesis and signaling and phenolic compound biosynthesis and polymerization. Enzyme activities for key genes in ethylene and phenolic compound biosynthesis and polymerization also increased due to wounding. Results indicate that wounding causes a major reallocation of metabolism in sugarbeet taproots. Although both ethylene and JA are likely involved in triggering wound responses, the greater and more sustained upregulation of ethylene biosynthesis and signaling genes relative to those of JA, suggest a preeminence of ethylene signaling in wounded sugarbeet roots. Changes in gene expression and enzymes involved in phenolic compound metabolism additionally indicate that barriers synthesized to seal off wounds, such as suberin or lignin, are initiated within the first 24 h after injury., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Fugate, Finger, Lafta, Dogramaci and Khan.)

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., Competing Interests: The authors declare there are no competing interests.

Although respiration is the principal cause of the loss of sucrose in postharvest sugarbeet ( Beta vulgaris L.), the internal mechanisms that control root respiration rate are unknown. Available evidence, however, indicates that respiration rate is likely to be controlled by the availability of respiratory substrates, and glycolysis has a central role in generating these substrates. To determine glycolytic changes that occur in sugarbeet roots after harvest and to elucidate relationships between glycolysis and respiration, sugarbeet roots were stored for up to 60 days, during which activities of glycolytic enzymes and concentrations of glycolytic substrates, intermediates, cofactors, and products were determined. Respiration rate was also determined, and relationships between respiration rate and glycolytic enzymes and metabolites were evaluated. Glycolysis was highly variable during storage, with 10 of 14 glycolytic activities and 14 of 17 glycolytic metabolites significantly altered during storage. Changes in glycolytic enzyme activities and metabolites occurred throughout the 60 day storage period, but were greatest in the first 4 days after harvest. Positive relationships between changes in glycolytic enzyme activities and root respiration rate were abundant, with 10 of 14 enzyme activities elevated when root respiration was elevated and 9 glycolytic activities static during periods of unchanging respiration rate. Major roles for pyruvate kinase and phosphofructokinase in the regulation of postharvest sugarbeet root glycolysis were indicated based on changes in enzymatic activities and concentrations of their substrates and products. Additionally, a strong positive relationship between respiration rate and pyruvate kinase activity was found indicating that downstream TCA cycle enzymes were unlikely to regulate or restrict root respiration in a major way. Overall, these results establish that glycolysis is not static during sugarbeet root storage and that changes in glycolysis are closely related to changes in sugarbeet root respiration.

Injury to plant products by harvest and postharvest operations induces respiration rate and increases the demand for respiratory substrates. Alterations in primary carbon metabolism are likely to support the elevated demand for respiratory substrates, although the nature of these alterations is unknown. To gain insight into the metabolic changes that occur to provide substrates for wound-induced increases in respiration, changes in the concentrations of compounds that are substrates, intermediates or cofactors in the respiratory pathway were determined in sugarbeet (Beta vulgaris L.) roots in the 4days following injury. Both wounded and unwounded tissues of wounded roots were analyzed to provide information about localized and systemic changes that occur after wounding. In wounded tissue, respiration increased an average of 186%, fructose, glucose 6-phosphate, ADP and UDP concentrations increased, and fructose 1,6-bisphosphate, triose phosphate, citrate, isocitrate, succinate, ATP, UTP and NAD(+) concentrations decreased. In the non-wounded tissue of wounded roots, respiration rate increased an average of 21%, glucose 6-phosphate, fructose 6-phosphate, glucose 1-phosphate and ADP concentrations increased, and isocitrate, UTP, NAD(+), NADP(+), and NADPH concentrations declined. Changes in respiration rate and metabolite concentrations indicated that localized and systemic changes in primary carbon metabolism occurred in response to injury. In wounded tissue, metabolite concentration changes suggested that activities of the early glycolytic enzymes, fructokinase, phosphofructokinase, phosphoglucose isomerase, and phosphoglucomutase were limiting carbon flow through glycolysis. These restrictions in the respiratory pathway, however, were likely overcome by use of metabolic bypasses that allowed carbon compounds to enter the pathway at glycolytic and tricarboxylic acid (TCA) cycle downstream locations. In non-wounded tissue of wounded roots, metabolic concentration changes suggested that glycolysis and the TCA cycle were generally capable of supporting the small systemic elevation in respiration rate. Although the mechanism by which respiration is regulated in wounded sugarbeet roots is unknown, localized and systemic elevations in respiration were positively associated with one or more indicators of cellular redox status., (Published by Elsevier Ltd.)

We recently described a new source of host-plant resistance to the Colorado potato beetle, Leptinotarsa decemlineata (Say), in a tetraploid potato (Solanum tuberosum L.) selection, ND2858-1. This genotype, and selected backcross progeny, had little damage while check cultivars were defoliated in open-choice field assays. To further characterize the observed deterrence, we determined foliar glycoalkaloids and conducted no-choice assays with ND2858-1 backcross progeny genotypes (ND4382-n). Development of neonate L. decemlineata in detached leaf assays on resistant progeny genotypes was delayed and larval weight gain after 4 d was inhibited by 75% relative to larval development and weight gain on susceptible genotypes. Inhibition of larval development in detached leaf assays with the selected progeny genotypes was equivalent to that of high-leptine genotypes of S. chacoense Bitter. Foliar glycoalkaloids of resistant genotypes included low levels of leptines I and II. The unlikely nature of this cross and the presence of leptine in this and resistant progeny selections cast doubt on the recorded pedigree. Molecular analyses were conducted by restriction fragment-length polymorphism and amplified fragment-length polymorphisms. Both methods established a high degree of relatedness to S. tuberososum and S. chacoense but not to S. fendleri. We conclude that ND2858-1 did not originate from a cross with S. fendleri, but is likely derived from S. chacoense. Oviposition and larval survival were reduced when adult L. decemlineata were placed in cages with resistant genotypes; an effect that was enhanced by inclusion of Perillus bioculatus F. Therefore, the nonpreference previously observed in open-choice field defoliation assays is also associated with antibiotic effects on L. decemlineata. The resistance may be caused by leptines, but is greater than would be expected by the leptine content. This source of host plant resistance could be a cost-effective management strategy, especially if combined with other resistance mechanisms or compatible control measures to delay development of resistance in the target insects.

This study was undertaken to determine the role of sucrose-metabolizing enzymes in altered carbohydrate partitioning caused by heat stress. Potato (Solanum tuberosum L.) genotypes characterized as susceptible and tolerant to heat stress were grown at 19/17[deg]C, and a subset was transferred to 31/29[deg]C. Data were obtained for plant growth and photosynthesis. Enzyme activity was determined for sucrose-6-phosphate synthase (SPS) in mature leaves and for sucrose synthase, ADP-glucose pyrophosphorylase, and UDP-glucose pyrophosphorylase in developing tubers of plants. High temperatures reduced growth of tubers more than of shoots. Photosynthetic rates were unaffected or increased slightly at the higher temperature. Heat stress increased accumulation of foliar sucrose and decreased starch accumulation in mature leaves but did not affect glucose. SPS activity increased significantly in mature leaves of plants subjected to high temperature. Changes in SPS activity were probably not due to altered enzyme kinetics. The activity of sucrose synthase and ADP-glucose pyrophosphorylase was reduced in tubers, albeit less quickly than leaf SPS activity. There was no interaction of temperature and genotype with regard to the enzymes examined; therefore, observed differences do not account for differences between genotypes in heat susceptibility.