Location: Sugarbeet and Potato Research
2020 Annual Report
Objectives
Objective 1: Identify genes and metabolic pathways responsible for deterioration of sugar beet root quality in storage, and develop new and more efficient storage protocols for wounded and drought-stressed sugar beet roots.
Objective 2: Develop and release superior sugar beet germplasm with improved genetic diversity, resistance to the sugar beet root maggot, and improved processing quality.
Objective 3: Develop physiological methods that promote and enhance natural plant defense mechanisms of sugar beet, including manipulation by plant hormones.
Objective 4: Develop genomic and transcriptomic resources to better identify fungicide-resistant and fungicide-sensitive strains of Cercospora beticola.
Objective 5: Facilitate the development of improved sugarbeet disease resistance to C. beticola through comparative genomics, transcriptomics, and pathogenicity studies on strains isolated from wild sea beet and cultivated sugarbeet germplasm.
Objective 6: Develop improved sugarbeet resistance to C. beticola using effector-based screening.
Objective 7: Facilitate the development of improved sugar beet disease resistance to Beet necrotic yellow vein virus and other important pathogens through comparative genomics and pathogenicity studies and the use of gene editing to manipulate promising candidate genes.
Approach
The sugarbeet industry is a significant contributor to the U.S. economy and ensures a domestic supply for a staple in the American diet. The industry’s future, however, is challenged by stagnant sugar prices, increasing production costs, and competition from alternative sweeteners, sugarcane and imported sugar. Increased productivity is essential for the industry to remain profitable, competitive and sustainable. Sugarbeet productivity is determined by the quantity of sugar produced after processing. This yield, the extractable sugar yield, depends on sucrose accumulation during production, sucrose retention during storage, and sucrose recovery during processing. Physiological and genetic research is proposed that potentially will lead to new production and storage protocols and new hybrids to improve sucrose accumulation, retention, and recovery during production, storage, and processing. Specifically, the proposed research will (1) increase production yield by (a) generating genetically diverse germplasm with unique disease, pest, and stress resistance genes, (b) creating improved breeding lines with resistance to the sugarbeet root maggot, and (c) utilizing plant hormones to induce native plant defense mechanisms to enhance yield; (2) reduce storage losses by (a) identifying genetic and metabolic pathways responsible for sucrose and quality losses during storage, (b) characterizing temperature effects on postharvest wound-healing, (c) determining preharvest drought effects on storage properties, and (d) evaluating the effects of defense-inducing plant hormones on storage properties; and (3) improve sucrose recovery by creating germplasm lines with reduced concentrations of compounds that prevent the extraction of a portion of the sucrose during processing.
Progress Report
Significant progress was made on research Objectives 1, 3, 4, 5, and 6 during fiscal year 2020. In Objective 1A, research to understand the molecular events involved in sugarbeet postharvest deterioration advanced. A determination of the effect of storage temperature, storage duration, and deterioration in root quality on the global expression of RNA transcripts and metabolites resulted in the identification of genes potentially involved in postharvest sucrose loss, raffinose accumulation, and respiratory losses. Identified genes include those that produce protein products involved in sucrose transport, raffinose biosynthesis and catabolism, and two enzymatic steps in the glycolytic pathway. Experiments conducted under Objective 1A also demonstrated that resistance against two common sugarbeet root storage rot pathogens declined during storage. In Objective 1B, research investigating the effect of storage temperature on sugarbeet root wound healing was completed. This research established that rapid cooling of sugarbeet roots after harvest slows and impairs healing of root injuries that are commonly incurred during harvest and piling operations. Cooling roots too rapidly after harvest, therefore, can promote storage losses since incomplete healing of wounds allows roots to dehydrate and provides entry sites for storage pathogens. Under Objective 3, a repetition of field and storage studies to evaluate the effects of methyl jasmonate (MeJA) and salicylic acid (SA) applications on sugarbeet root yield, sucrose content, sucrose yield, and storage properties was conducted, completing the second year of a three-year study. In Objective 4A, fungicide resistance was calculated for nearly 200 strains of the Cercospora leaf spot pathogen Cercospora beticola, which identified an increasing trend of resistance to several classes of commonly used fungicides for disease management. Under Objective 5B, virulence of sea beet- and sugarbeet-adapted strains of Cercospora were inoculated onto sugarbeet and sea beet. This research established that sea beet may act as a reservoir for highly virulent strains of Cercospora since sea beet-adapted strains were more aggressive on sugarbeet than sugarbeet-adapted strains of the fungus. Research conducted under Objective 6B identified and characterized a new gene involved in the biosynthesis of the toxin cercosporin that is produced by Cercospora during infection of sugarbeet. This research established several additional genes in the cercosporin biosynthesis pathway, which will be critical in the development of germplasm that is resistant to this toxin.
Accomplishments
1. New technologies to rapidly identify Cercospora and mutations associated with fungicide resistance. Cercospora leaf spot (CLS), caused by the fungal pathogen Cercospora beticola, is the most destructive disease of sugarbeet worldwide. Although growing CLS-tolerant varieties is helpful, disease management currently requires timely application of fungicides. However, overreliance on fungicides has led to the emergence of fungicide resistance in many C. beticola populations, resulting in multiple epidemics in recent years. To address this issue, ARS scientists in Fargo, North Dakota, developed a fungicide resistance management 'toolbox' for early detection of C. beticola in sugarbeet leaves and mutations associated with commonly used fungicides for CLS management. Methods were developed to detect the pathogen as early as one day post-inoculation in field settings. This research provides a low-tech methodology that can be used by agricultural field staff or growers to quickly identify the pathogen in the field, which is critically important for disease management.
2. Rapid cooling of harvested sugarbeet roots impedes wound healing. Nearly all sugarbeet roots are wounded from mechanical harvesting and piling operations, and the healing of these injuries is necessary to limit root dehydration and microbial infection during storage. Although storage temperature is known to influence wound healing in other crops, little is known of the effect of temperature on wound healing in sugarbeet roots. To address this deficiency, ARS scientists in Fargo, North Dakota, evaluated the effect of storage temperature on the rate and extent of the physiological processes that contribute to wound healing in sugarbeet roots using temperatures typical of freshly harvested and rapidly cooled roots. Rapid cooling of roots after harvest significantly slowed and impaired wound healing processes to such an extent that roots were unable to completely seal off wound sites even after 28 days in storage, while roots stored at the higher temperatures typical at the time of harvest rapidly and completely sealed off injuries. Although storage pile managers typically try to cool sugarbeet root piles as rapidly as possible, this research provides warning to the industry that lowering the temperature of roots too quickly after harvest can exacerbate root desiccation and the development of storage diseases and lead to increased losses during storage.
Review Publications
Fugate, K.K., Eide, J.D., Martins, D.N., Grusak, M.A., Deckard, E.L., Finger, F.L. 2019. Colocalization of sucrose synthase expression and sucrose storage in the sugarbeet taproot indicates a potential role for sucrose catabolism in sucrose accumulation. Journal of Plant Physiology. 240:153016. https://doi.org/10.1016/j.jplph.2019.153016.
Shrestha, S., Neubauer, J., Spanner, R., Natwick, M.B., Rios, J., Metz, N., Secor, G., Bolton, M.D. 2020. Rapid detection of Cercospora beticola in sugar beet and mutations associated with fungicide resistance using LAMP or probe-based qPCR. Plant Disease. 104:6. https://doi.org/10.1094/PDIS-09-19-2023-RE.
Weiland, J.J., Bornemann, K., Neubauer, J., Khan, M., Bolton, M.D. 2019. Prevalence and distribution of beet necrotic yellow vein virus strains in North Dakota and Minnesota. Plant Disease. 103:2083-2089. https://doi.org/10.1094/PDIS-02-19-0360-RE.
Weiland, J.J., Sharma Poudel, R., Flobinus, A., Cook, D., Secor, G., Bolton, M.D. 2020. RNAseq analysis of rhizomania-infected sugar beet provides the first genome sequence of beet necrotic yellow vein virus from the USA and identifies a novel Alphanecrovirus and putative satellite viruses. Viruses. 12(6):626. https://doi.org/10.3390/v12060626.
Lafta, A.M., Khan, M., Fugate, K.K. 2020. Dehydration during storage affects carbohydrate metabolism and the accumulation of non-sucrose carbohydrates in postharvest sugarbeet roots. Journal of Agriculture and Food Research. 2:100047. https://doi.org/10.1016/j.jafr.2020.100047.
Fugate, K.K., Campbell, L.G., Covarrubias-Pazaran, G., Rodriguez-Bonilla, L., Zalapa, J.E. 2019. Genetic differentiation and diversity of sugarbeet germplasm resistant to sugarbeet root maggot. Plant Genetic Resources. 17(6):514-521. https://doi.org/10.1017/S1479262119000388.
Webb, K.M., Shrestha, S., Trippe III, R.C., Rivera-Varas, V., Covey, P.A., Freeman, C.N., De Jonge, R., Secor, G.A., Bolton, M.D. 2019. Phylogenetic relationships and virulence assays of Fusarium secorum from sugar beet suggests a new look at species designations. Plant Pathology. 68(9):1654-1662. https://doi.org/10.1111/ppa.13082.
Rangel, L., Spanner, R.E., Ebert, M., Pethybridge, S.J., Stukenbrock, E.H., De Jonge, R., Secor, G.A., Bolton, M.D. 2020. Cercospora beticola: The intoxicating lifestyle of the leaf spot pathogen of sugar beet. Molecular Plant Pathology. 21:1020-1041. https://doi.org/10.1111/mpp.12962.
