Location: Sugarbeet and Potato Research
2019 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 FY2019. No progress was made on Objective 2 due to a critical vacancy created by the FY2018 retirement of the project’s Research Plant Geneticist. No progress was made on Objective 7 because this objective represents a new Research Plant Pathologist position that has not been recruited yet. All project objectives fall under NP301, with Objectives 3-7 additionally contributing to NP303. In Objective 1A, research to understand the molecular events involved in postharvest deterioration advanced. A total of 42 root samples exhibiting variable levels of deterioration were subjected to RNA sequencing and metabolomic analysis resulting in the identification of more than 5000 genes that were differentially expressed and 379 metabolites that changed in concentration during storage. Storage-related changes in cell wall properties and components were also determined. Analysis of the collected data continues but has already revealed the likely importance of sucrose transporters during postharvest sugarbeet root storage. In Objective 1B, the effect of storage temperature on sugarbeet root wound healing progressed with an investigation into the effect of temperature on enzymes that contribute to the biosynthesis of polymeric compounds that plants utilize to close wound sites. This research demonstrated that low storage temperature reduces polyphenol oxidase activity in concert with a slowing of melanin biosynthesis in stored roots. Research was initiated to determine the effects of preharvest water stress on sugarbeet root storage properties, in research described in Objective 1C of the project plan. As these studies are ongoing, no results are available at the time of writing. Under Objective 3, a repetition of field and storage studies to determine the effects of methyl jasmonate (MeJA) and salicylic acid (SA) applications on sugarbeet root yield, sucrose content, sucrose yield, and storage properties was completed. Under Objective 4, more than three hundred Cercospora strains were harvested from diseased leaves, DNA extracted, and clones identified and discarded. Under Objective 5, genome sequencing and bioinformatics was completed for eight Cercospora strains harvested from sea beet. Genomes of Cercospora populations on cultivated and sea beet exhibit similar amounts of genetic variation and appear to be closely-related. However, some genomic regions exhibit a higher extent of sequence divergence, suggesting they may be under divergent selection during recent adaptation to these distinct hosts. Under Objective 6, mass spectrometry analyses identified a cercosporin-like metabolite that accumulated specifically in the mutant strain. This will facilitate further characterization of this metabolite.
Accomplishments
1. Identification of a novel pathogen protein that induces necrosis in sugar beet leaves. Cercospora beticola causes the most important foliar disease of sugar beet worldwide. Despite the economic importance of this pathogen, the pathology of this fungus is largely unknown. ARS scientists in Fargo, North Dakota, identified a novel protein from this pathogen that causes damaging lesions in sugar beet leaves. Cercospora mutants lacking the gene encoding this protein were less virulent, underscoring the importance of this gene for the disease to occur. Identification of how this protein works may provide a means to breed for durable resistance to this serious disease.
Review Publications
Heidari, B., Miras Moreno, M., Lucini, L., Bolton, M.D., McGrath, J.M., Broccanello, C., Alberti, I., Sella, L., Concheri, G., Stevanato, P. 2019. Mass spectrometry-based metabolomic discrimination of Cercospora leaf spot resistant and susceptible sugar beet germplasms. Euphytica. 215:25. https://doi.org/10.1007/s10681-019-2351-3.
Campbell, L.G., Fugate, K.K. 2018. Root yield and quality of sugarbeet hybrids with pollinators selected for sodium, potassium, or amino-nitrogen concentration. Journal of Sugar Beet Research. (1-2): 3-18.
Campbell, L.G., Fugate, K.K. 2018. Sugarbeet germplasm lines selected from crosses between wild Beta vulgaris subsp. maritima from France, Belgium, and Denmark and cultivated sugarbeet. Journal of Sugar Beet Research. 55 (3-4):3-20.
Ebert, M.K., Spanner, R.E., De Jonge, R., Smith, D.J., Holthusen, J.E., Secor, G.A., Thomma, B.P., Bolton, M.D. 2019. Gene cluster conservation identifies melanin and perylenequinone biosynthesis pathways in multiple plant pathogenic fungi. Environmental Microbiology. 21(3):913-927. https://doi.org/10.1111/1462-2920.14475.
Knight, N.L., Vaghefi, N., Kikkert, J.R., Bolton, M.D., Secor, G.A., Rivera, V.V., Hanson, L.E., Nelson, S.C., Pethybridge, S.J. 2019. Genetic diversity and structure in regional Cercospora beticola populations from Beta vulgaris ssp. vulgaris suggest two clusters of separate origin. Phytopathology. 109:1280-1292. https://doi.org/10.1094/PHYTO-07-18-0264-R.
Fazio, G., Lordan, J., Grusak, M.A., Francescatto, P., Robinson, T. 2019. Mineral nutrient profiles and relationships of ‘Honeycrisp’ grown on a genetically diverse set of rootstocks under Western New York climatic conditions. Horticulture Scientia. https://doi.org/10.1016/j.scienta.2019.05.004.
Narayanan, N., Beyene, G., Chauhan, R., Gaitan-Solis, E., Gehan, J., Butts, P., Siritunga, D., Okwuonu, I., Woll, A., Jimenez-Aguilar, D.M., Boy, E., Grusak, M.A., Anderson, P., Taylor, N.J. 2019. Biofortification of field-grown cassava by engineering expression of an iron transporter and ferritin. Nature Biotechnology. 37:144-151. https://doi.org/10.1038/s41587-018-0002-1.
