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

2023 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
Research conducted over the five-year life of the project successfully met all Project Plan objectives and generated information and genetic resources that promote improvements in sugarbeet industry productivity and sustainability. This project is now replaced by project 3060-21000-045-000D, “Improving sugarbeet productivity and sustainability through genetic, genomic, physiological, and phytopathological approaches.” Postharvest storage experiments conducted under Objective 1 revealed the exceptionally numerous and diverse changes in gene expression and biochemical composition that occur during sugarbeet root storage. In total, 8,656 genes and 382 metabolites were identified that change in expression or concentration during storage, including genes and metabolites involved in sucrose loss, root softening, respiration, and susceptibility to storage diseases. Additionally, Objective 1 research demonstrated that (1) wound healing in harvested sugarbeet roots is delayed and impaired when roots are rapidly cooled after harvest, thereby facilitating root dehydration and storage disease development, (2) pre-harvest drought stress increases sugarbeet root respiration rate and susceptibility to rots during storage, (3) sucrose and quality losses during storage are not impacted by preharvest Cercospora beticola infection, indicating that no special storage precautions are needed for roots obtained from plants infected with this pathogen, and (4) regulatory and respiratory pathway genes differ in roots with genetic differences in storage respiration rates, identifying candidates for the genes responsible for inherent differences in storage respiration rate. Under Objective 2, eight breeding lines derived from crosses between cultivated sugarbeet and wild sea beet were evaluated for Rhizoctonia root and crown rot (RRCR) at two locations (Crookston, Minnesota and Kimberly, Idaho), with three lines found to be resistant to RRCR in Crookston, Minnesota, and moderately resistant in Kimberly, Idaho. Twenty-three lines derived from crosses between sugarbeet root maggot (SBRM)-resistant and RRCR-resistant germplasm were evaluated for both RRCR and SBRM, with one line exhibiting good resistance to both parasites, two lines displaying good resistance to SBRM but moderate resistance to RRCR, one line with moderate resistance to both parasites, and nine lines that were resistant to SBRM only. Two lines differing in concentrations of root impurities that were developed in previous years were further evaluated in Crookston, Minnesota, and St. Thomas, North Dakota, for root yield, sucrose content, and LTM (lose to molasses) and differences between the two lines that were detected in previous years were confirmed. These two lines are ready for release as genetic stocks for use in analyzing genetic control of impurities to generate important information for breeding sugarbeet varieties with low LTM values. A manuscript describing this germplasm release is in preparation. Under Objective 3, research into the use of the phytohormones methyl jasmonate and salicylic acid as protectants from environmental stresses determined that neither hormone consistently improved sugarbeet root or sucrose yield at harvest or reduced storage loss and deterioration. Although these compounds are beneficial in other crops, they show little promise for improving sugarbeet productivity. Under Objective 4, fungicide resistant mutations located in the CbCyp51 gene were further dissected and various mutation combinations were found to not only contribute to varying levels of fungicide resistance, but also contribute to resistance to different fungicide chemistries. The identified mutations have been developed into rapid molecular assays that can be used to determine the fungicide resistance profiles of sugarbeet leaf field samples infected with C. beticola, providing a tool for growers when making decisions regarding fungicide applications. Objective 5 was completed in 2021 and showed that C. beticola isolates collected from different host species did not significantly differ in their virulence on cultivated sugarbeet lines. Under Objective 6, C. beticola effector genes were screened via infiltration of Nicotiana benthamiana leading to the identification of new pathogen effector proteins that induce necrosis. Under Objective 7, three new viruses were identified that coexist with Beet necrotic yellow vein virus (BNYVV), the causal agent of rhizomania in sugarbeet and table beet, indicating the complexity of the disease due to mixed infections and the potential threat of mixed infections to sugarbeet production. The identified new viruses are Tomato bushy stunt virus, that coexists with BNYVV in sugarbeet grown in California, and Pepper yellow dwarf strain of Beet curly top virus and Spinach curly top Arizona virus that coexist with rhizomania in table beet grown in sugarbeet growing regions of Idaho. Further, a new method to detect BNYVV, the causal agent of rhizomania, was developed utilizing clustered regularly interspaced short palindromic repeats (CRISPR)-associated technology. Evaluation of the method using greenhouse grown plants produced from seed sown on soil collected from rhizomania-infested fields established its ability to detect BNYVV with high sensitivity and specificity under isothermal conditions without the need for sophisticated instrumentation.

Accomplishments
1. New fungicide resistance assays to improve control of a major sugarbeet pathogen. Recent rises in fungicide resistance in Cercospora beticola, the pathogen responsible for Cercospora leaf spot (CLS) disease of sugarbeet, is a major challenge for sugarbeet growers. Knowledge of the level of fungicide resistance is necessary for optimum management of the disease, but current methods to detect fungicide resistance are labor intensive and too slow to provide resistance information to growers in a timely manner. ARS researchers in Fargo, North Dakota, developed rapid assays to identify resistance in C. beticola strains to several fungicides. These improved assays provide a powerful tool for determining appropriate fungicide applications based on the resistance profile of a given sugarbeet field, thereby saving sugarbeet growers money by only applying efficacious fungicides.

2. Sugarbeet root storage losses are not accelerated by Cercospora leaf spot. Cercospora leaf spot (CLS) is a fungal disease of sugarbeet that reduces root yield and sugar accumulation during production and costs the U.S. sugarbeet industry an estimated $79 million annually. With the pathogen responsible for CLS widely distributed in U.S. sugarbeet production regions and difficult to control, roots from plants with CLS are inevitably incorporated into sugarbeet storage piles, even though the effects of the disease on root storage properties are unknown. To provide guidance to the industry for the storage of roots harvested from CLS-diseased plants, ARS scientists in Fargo, North Dakota, determined the effects of CLS on the ability of sugarbeet roots to retain sucrose and processing quality during postharvest storage. The research generated clear evidence that CLS does not accelerate sucrose loss or processing quality deterioration, even after prolonged storage of roots from severely diseased plants. These results provide the sugarbeet industry with evidence that roots harvested from plants with CLS can be stored without additional or specialized precautions, regardless of CLS symptom severity.

3. An improved genotyping platform to assist plant breeders. Single nucleotide polymorphisms (SNPs) are a type of mutation that are abundantly interspersed throughout plant DNA and can be exploited for plant breeding because they often closely associate with genes that confer desirable traits. Consequently, plant breeders expend considerable effort to develop protocols to accurately identify SNPs with greater efficiency and at a lower cost. ARS scientists in Fargo, North Dakota, simplified SNP detection in sugarbeet with the development of new protocols that allows them to be detected quickly using affordable, readily available lab equipment rather than the high-tech and expensive laboratory instruments previously used. This improved SNP detection method has proven to be effective in advancing sugarbeet breeding efforts and can also be used for the improvement of other crops.

4. Identification of new viruses infecting sugarbeet and table beet. Rhizomania, a viral disease that severely reduces root and sucrose yield of the sugarbeet crop, is managed through host resistance globally. Although Beet necrotic yellow vein virus (BNYVV) is considered the causal agent of rhizomania, additional viruses coexist in sugarbeet fields and may influence disease symptomology and severity. ARS scientists in Fargo, North Dakota, conducted a field survey of rhizomania-diseased beets and identified Tomato bushy stunt virus (TBSV) as a new virus that has adapted to sugarbeet and naturally coexists with BNYVV. Two additional viruses, Pepper yellow dwarf strain of Beet curly top virus (BCTV-PeYD) and Spinach curly top Arizona virus (SpCTAV), were identified that coexist with BNYVV in table beets. The identification of new viruses that are adapted to sugarbeet and table beet indicate the possible complexity of controlling rhizomania due to mixed infections and the potential threat of this disease to sugarbeet production.

5. Identification of pathogens and microbes in sugarbeet storage and processing facilities. Harvested sugarbeet roots are stored for up to 240 days in outdoor piles or ventilated sheds, after which they are sliced and extracted in factories to produce sugar. Fungal and bacterial pathogens and other microbes that are present in storage piles and the factory, however, cause sucrose to be consumed and can lead to an accumulation of impurity compounds that hinder sugar recovery. Very few studies have examined the pathogens and microbes present in storage piles and sugar factories, but their identity is needed to develop protocols to control their growth. To address this knowledge gap, ARS researchers in Fargo, North Dakota, identified major microbial communities responsible for root deterioration and sugar loss in storage piles and the processing streams of sugarbeet factories. This information provides the impetus for the development of new strategies to mitigate storage diseases and microbial contamination in factories to maximize recoverable sugar yield.

U.S. DEPARTMENT OF AGRICULTURE

Sugarbeet and Potato Research: Fargo, ND