Project : USDA ARS

ARS Home » Plains Area » Fargo, North Dakota » Edward T. Schafer Agricultural Research Center » Sugarbeet and Potato Research » Research » Research Project #434569

Research Project: Increasing Sugar Beet Productivity and Sustainability through Genetic and Physiological Approaches

Location: Sugarbeet and Potato Research

2021 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 all research objectives in fiscal year (FY) 2021. In Objective 1A, research to understand the molecular events involved in sugarbeet postharvest deterioration identified 287 differentially expressed genes in sugarbeet roots with genetic differences in storage respiration rate. Among these genes were two glycolytic genes which directly participate in the formation of respiratory substrates. These genes were strongly upregulated in a high-respiring sugarbeet line relative to a low-respiring line, with transcriptional upregulation associated with enhanced enzyme activity. Understanding the role of sugar transporters in postharvest sucrose losses advanced with the cloning of sugar transporter genes. These genes were tagged with a fluorescent marker to allow determination of their cellular location and aid in understanding their function in postharvest sugarbeet roots. Under Objective 1C, research demonstrated that preharvest drought stress increases sugarbeet root storage respiration rate, with the impact on respiration rate dependent upon both the severity of drought stress and time in storage. In Objective 2A, eight broad-based populations were selected from crosses between cultivated sugarbeet and wild germplasm lines, and the genetic diversity of these populations was analyzed using genetic markers generated by a genotype-by-sequencing strategy. Under Objective 2B, forty populations were selected after evaluating their resistance to sugarbeet root maggot (SBRM) feeding. These populations were derived from crosses between sugarbeet lines with resistance either to SBRM or the root rot pathogen Rhizoctonia solani. Seeds of these selections were produced in a greenhouse for future evaluation of resistance to R. solani, which may result in new sugarbeet lines with resistance to both SBRM and R. solani. In Objective 2C, breeding for improved processing properties advanced with the selection of populations with low and high root non-sucrose impurity content. Seeds from the two populations were increased for future yield trials and impurity evaluations. 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 last year of a three-year study. In Objective 4B, a genome wide association study (GWAS) was conducted using over 200 strains of Cercospora beticola with differing levels of resistance to demethylation inhibitor (DMI) fungicides. This research identified five genes highly associated with DMI resistance. In Objective 5B, greenhouse assays using C. beticola isolates harvested from sea beet were compared to sugarbeet-derived isolates, which showed that host origin did not significantly impact virulence. In Objective 6A, agroinfiltration constructs were developed and will be used to test the ability of this technology to deliver C. beticola genes transiently into Nicotiana benthamiana. Under Objective 7, a genome editing-based, isothermal, next-generation diagnostic assay was developed for detecting beet necrotic yellow vein virus (BNYVV), the causal agent for rhizomania in sugarbeet. The assay utilizes clustered regularly interspaced short palindromic repeats-associated protein (CRISPR-Cas) technology and allows for sensitive and specific detection of BNYVV using methodology that is amenable to high-throughput analysis without sophisticated instrumentation. The detection method was validated using greenhouse grown plants produced from seed sown on soil samples collected from rhizomania-infested fields.

Accomplishments
1. Seed-borne Cercospora beticola can initiate Cercospora leaf spot (CLS) in sugarbeet. CLS is a globally important disease of sugarbeet caused by the fungus Cercospora beticola. Long-distance movement of C. beticola has been indirectly evidenced in recent population genetic studies, suggesting the potential for dispersal via seed. To assess whether CLS can be seed-borne, ARS scientists in Fargo, North Dakota, screened commercially available seed lots obtained from Europe and the United States for C. beticola. These assays identified several varieties that were infested with C. beticola. Additionally, planting infested seeds caused CLS to develop in adult plants, confirming that this disease can be seed-borne. This research provides important evidence that seed-borne inoculum should be considered when implementing integrated disease management strategies for CLS.

U.S. DEPARTMENT OF AGRICULTURE

Sugarbeet and Potato Research: Fargo, ND