Location: Sugarbeet and Potato Research2016 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 was made on all research objectives. Evaluation of the use of salicylic acid (SA) to prevent storage rot is complete (Objective 1a). SA reduced rot due to Botrytis cinerea, Penicillium claviforme, and Phoma betae when roots were water stressed prior to harvest. SA, however, had no effect on rot symptoms in unstressed roots. Experiments to evaluate the ability of methyl jasmonate (MeJA) or SA to alleviate the negative effects of insufficient water, saline soil, or cold temperatures were conducted. Both seed and seedling treatments with MeJA or SA were investigated and data analysis of these experiments is in progress (Objective 1b). Jasmonic acid (JA)-induced changes to the sugarbeet root transcriptome were determined to elucidate the defense mechanisms induced by this hormone. A total of 78 JA-induced defense genes were identified and a subset of these genes was validated by qRT-PCR (Objective 1c). Metabolic profiles for roots with differing respiration rates have been generated to provide insight into factors that regulate sugarbeet root respiration rate in storage. For this experiment, data has been compiled and its analysis is in progress (Objective 2a). An investigation into the effect of Rhizoctonia root and crown rot on sugarbeet root storage properties is complete and correlations between disease severity and changes in storage properties have been determined (Objective 2b). The first repetition of an experiment investigating environmental conditions affecting leaf regrowth on stored roots is complete. This experiment generated evidence for the effect of storage temperature on leaf regrowth (Objective 2c). Lines previously identified as having low concentrations of sodium, potassium, or amino-nitrogen (often referred to as impurities) in their roots were crossed with a common female parent to determine the expression of these impurity traits in a hybrid. These hybrids have been evaluated in yield trials. Sodium, potassium, and amino-nitrogen prevent the extraction of sucrose during processing; therefore reduced levels of these impurities would increase processing efficiency (Objective 3). Eleven breeding populations selected from crosses between a cultivated sugarbeet line and wild Beta accessions originating from France, Belgium, and Denmark are being evaluated in replicated yield trials for a second year (Objective 4a). Promising lines will be increased for eventual release to the public. These lines, along with previously released germplasm, will provide additional unique sources of genetic variation that will allow breeders to introduce diversity into their elite populations and parental lines. Selection for sugarbeet root maggot resistance continues in populations formed by crossing previously released root maggot resistant germplasm with breeding lines from other USDA breeding programs (Objective 4b). The intent is to combine root maggot resistance with resistance to prevalent diseases and to increase the sugar concentration of currently available root maggot resistant germplasm. Accessions identified as sugarbeet root maggot resistant in the Sugarbeet Crop Germplasm Committee’s Beta screening program are being further examined and those with confirmed resistance to the root maggot will be identified to the public and incorporated into the resistance breeding program (Objective 4).
1. New sugarbeet breeding line with enhanced resistance to the sugarbeet root maggot. The sugarbeet root maggot (SBRM) is considered the most destructive insect pest of sugarbeet in North America. To combat this pest, a new sugarbeet breeding line, F1043, was developed by ARS researchers in Fargo, North Dakota as a new and unique source for genetic resistance against SBRM. F1043 was developed by multiple rounds of selection from an initial cross between PI 179180, a line with red globe-shaped roots that was identified as SBRM resistant in 1972, and C564aa, a SBRM-susceptible germplasm developed by ARS researchers in California. The SBRM resistance of F1043 is equal to the resistance of previously released SBRM resistant germplasm lines but is derived from a unique, unrelated source. New sources of resistance to pests or diseases are valuable to public and commercial breeders, especially when pest tolerance to a currently available resistance source increases, undesirable traits are linked to resistance in currently available SBRM-resistant germplasms, or the new source has superior combining ability with specific elite parental lines.
2. Nine new breeding lines that broaden the genetic base of the sugarbeet crop. The genetic base of the commercial sugarbeet crop is relatively narrow, limiting the genetic variability that is available for crop improvement through selective breeding and increasing the vulnerability of the crop to disease. To broaden the genetic base of the sugarbeet crop, ARS researchers in Fargo, North Dakota crossed the ARS sugarbeet line, R376-43, with nine wild Beta accessions originating from England, Wales, and the Channel Islands, and conducted multiple rounds of selection from these crosses to develop nine unique germplasm lines that incorporate wild germplasm (F1033, F1034, F1035, F1036, F1037, F1038, F1039, F1040, and F1041). Selections were made with regards to root shape, sucrose content, and root yield. Three-year average sucrose concentrations of the nine germplasm lines ranged from 96 to 88% of the sucrose concentration of a commercial hybrid, and average root yields ranged from 91% to 67% of the hybrid. These lines will provide unique sources of genetic variation that will allow breeders to incorporate additional diversity into their elite populations and parental lines and may be a source for new disease or pest resistance genes.
Fugate, K.K., Ribeiro, W.S., Lulai, E.C., Deckard, E.L., Finger, F.L. 2016. Cold temperature delays wound healing in postharvest sugarbeet roots. Frontiers in Plant Science. 7:499. doi: 10.3389/fpls.2016.00499.
Campbell, L.G., Fugate, K.K. 2015. Relationships among impurity components, sucrose, and sugarbeet processing quality. Journal of Sugar Beet Research. 52(1-2):2-21.
Campbell, L.G. 2015. F1030, F1031, and F1032 sugarbeet germplasms selected from crosses between L19 and three cultivated/wild germplasms. Journal of Plant Registrations. 9(3):382-387.