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ARS Home » Plains Area » Fargo, North Dakota » Edward T. Schafer Agricultural Research Center » Sugarbeet and Potato Research » Research » Research Project #425284

Research Project: Physiological and Genetic Approaches to Improving Extractable Sugar Yield in Sugarbeet

Location: Sugarbeet and Potato Research

2015 Annual Report

Objective 1: Identify physiological approaches for reducing sucrose loss due to storage rot and environmental stresses, including cold, drought, and soil salinity, using plant inducible defenses. Subobjective 1a: Determine the ability of jasmonic acid (JA) and salicylic acid (SA) to reduce the incidence and severity of storage rot due to Botrytis cinerea, Fusarium graminearum, Penicillium claviforme, and Phoma betae. Subobjective 1b: Determine the ability of jasmonic acid and salicylic acid to mitigate the impact of environmental stress caused by limited water availability, cold temperature, or high soil salinity. Subobjective 1c: Identify JA- and SA-induced biochemical and molecular changes associated with the induction of native defense responses by characterizing enzymes and gene products implicated in inducible defense responses via global transcriptional analysis. Objective 2: Identify the physiological mechanisms that regulate sugarbeet root respiration and resultant sucrose loss, and characterize the impact of Rhizoctonia root rot and leaf regrowth on sucrose loss during root storage in order to optimize storage management practices. Subobjective 2a: Identify enzymatic reactions and metabolic intermediates in sucrose catabolic pathways that may restrict root respiration rate. Subobjective 2b: Determine the effects of Rhizoctonia root and crown rot on root storage properties in relation to disease severity and duration of storage. Subobjective 2c: Determine the effect of postharvest leaf regrowth on sugarbeet root respiration and the effect of storage temperature on leaf regrowth. Objective 3: Characterize the root impurity components that interfere with sucrose extraction during processing, and develop germplasm with reduced concentrations of these compounds. Objective 4: Enhance the genetic diversity of breeding gene pools and breed genetically diverse sugarbeet lines with improved sugarbeet root maggot resistance. Subobjective 4a: Enhance the genetic diversity of breeding gene pools through introgression of exotic germplasm. Subobjective 4b: Through traditional breeding approaches, develop improved sugarbeet root maggot resistant germplasm.

The U.S. sugarbeet industry produces 60% of domestically grown sugar and nearly half of domestically consumed sugar. Thirty-two million tons of sugarbeet roots, valued at 2.1 billion dollars, are produced annually. The sugarbeet industry faces intense competition from alternative sweeteners and escalating production costs. For the industry to remain viable and to ensure a reliable, domestic supply of a staple in the American diet, increases in net productivity are essential. The yield of sugar produced after processing, or the extractable sucrose yield, determines net productivity for the sugarbeet crop. This yield depends on biomass and sucrose accumulation during production, sucrose retention during postharvest storage, and sucrose recovery during processing. The goal of research proposed in this project is to increase sugarbeet extractable sucrose yield by generating information and genetic resources that will lead to new production and storage protocols and improved hybrids for enhanced sucrose yield at harvest, improved sucrose retention during storage, and increased sucrose recovery during processing. Specific goals are to (1) determine the potential of inducible defense responses to reduce yield losses due to environmental stresses and storage rots, (2) determine the endogenous mechanisms that regulate root respiration during storage, (3) characterize the impact of Rhizoctonia root and crown rot and leaf regrowth on postharvest losses, (4) develop germplasm that facilitates improvements in processing quality, (5) develop germplasm that broadens the genetic base of sugarbeet, and (6) develop germplasm that combines high levels of sugarbeet root maggot resistance with resistance to prevalent diseases and improved sucrose concentration.

Progress Report
Progress was made on all research objectives. Exogenous application of salicylic acid (SA) was found to alleviate storage rot in water-stressed sugarbeet roots (Objective 1). SA application reduced the severity of rot symptoms due to the storage pathogens, Botrytis cinerea, Penicillium claviforme, and Phoma betae, by 54, 45, and 58%, respectively. However, SA did not reduce rot symptoms in unstressed roots, suggesting that SA alleviated the negative impact of water stress, but did not directly protect sugarbeet roots against storage rots. Previous research demonstrated the ability of exogenous application of jasmonic acid (JA) to reduce storage rot. To elucidate the defense mechanisms induced by JA, genes altered in expression by JA treatment were identified (Objective 1). A total of 182 up-regulated genes and 101 down-regulated genes were identified in JA-treated roots. Of these genes, 38 had putative defense functions. The impact of Rhizoctonia root and crown rot (RRCR) on sugarbeet postharvest storage properties was determined and found to be dependent on disease severity (Objective 2). Roots with mild RRCR symptoms exhibited small increases in respiration rate and sucrose loss in storage relative to healthy roots, but generally could be stored for prolonged periods. However, roots with moderate to severe RRCR symptoms had inordinately high respiration rates and extractable sucrose losses and accumulated high concentrations of carbohydrate impurities which impede sugarbeet root processing. These roots, with disease symptoms that covered more than 25% of the root surface, stored poorly, suggesting that roots with moderate or severe RRCR symptoms should be abandoned in the field, sent to the factory for immediate processing, or incorporated into storage piles only with extreme caution. A sugarbeet breeding line selected from a cross between PI 179180 and C564aa is being considered for release as a unique source of sugarbeet root maggot (SBRM) resistance (Objective 4). PI 179180, a line with red globe-shaped roots that was identified as resistant in 1972, was originally collected near Gemlik, Turkey. C564aa is a SBRM susceptible germplasm developed by USDA-ARS in California. Alternative sources of resistance to a pest or disease may be of value if the pest develops resistance to a widely used resistance source, if genes that result in undesirable traits are linked to the resistance genes, or if they have superior combining ability with specific elite parental lines. Based upon recent damage ratings, it appears that the SBRM resistance derived from PI 179180 is essentially equal to the resistance of previously released but unrelated SBRM resistant germplasm lines.

1. Severity of Rhizoctonia root and crown rot symptoms affects suitability of sugarbeet roots for storage. Rhizoctonia root and crown rot (RRCR) is a soilborne fungal disease of sugarbeet that is found in most, if not all, sugarbeet production areas in the U.S. Prior to this research, the U.S. sugar industry was faced with making decisions regarding the storage of roots with this disease with no knowledge of RRCR’s effects on postharvest storage. ARS scientists in Fargo, ND evaluated the effect of RRCR disease severity on sugar and quality losses during storage and root storageability and determined that roots with mild RRCR symptoms stored nearly as well as undiseased roots, but those with moderate to severe symptoms (i.e., symptoms that cover more than 25% of the root’s surface) stored poorly. The research provides guidance to the sugarbeet industry for managing the storage of sugarbeet roots with RRCR. The research also provides information that assists in determining the severity of RRCR disease symptoms that preclude storage or require segregation of roots for early processing, and helps growers whose roots are refused for storage justify their insurance claims.

Review Publications
Campbell, L.G., Windels, C.E., Fugate, K.K., Brantner, J.R. 2014. Postharvest losses associated with severity of Rhizoctonia crown and root rot of sugarbeet at harvest. Journal of Sugar Beet Research. 51(1-2):31:51.