Location: Sugarbeet and Potato Research2014 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.
Research was conducted to investigate the use of the plant hormone, jasmonic acid (JA), to induce native plant defenses and protect sugarbeet roots from storage rots (objective 1). JA treatments, applied to plants or roots, reduced the severity of storage rot due to three rot-causing pathogens. When applied to roots after harvest, JA reduced rot due to Botrytis cinerea, Penicillium claviforme, and Phoma betae by 51%, 44%, and 71%, respectively. Preharvest JA treatment to plant foliage reduced storage rot severity, but was generally less effective than postharvest treatment. The effectiveness of preharvest treatments depended on the time interval between JA application and harvest. Applied 7 days prior to harvest, JA reduced the severity of rot due to B. cinerea and P. betae by 55% and 65%, but had no significant effect on rot due to P. claviforme. Treatments applied 14 days prior to harvest reduced rot due to P. claviforme and P. betae by 14% and 45%, but did not affect rot severity due to B. cinerea. Research to identify the genes and proteins altered by JA treatment that contribute to sugarbeet root defenses against storage rot has been initiated. The effect of Rhizoctonia root and crown rot (RRCR) severity on postharvest storage losses was also investigated (objective 2). RRCR is a widespread and especially threatening fungal disease that develops during sugarbeet root production. Thirty days after harvest, the respiration rate of roots with severe disease symptoms was 213% greater than the respiration rate of healthy roots. The extractable sucrose concentration 30 days after harvest of roots with severe symptoms was 29% lower than that of healthy roots. Differences in respiration rate and extractable sucrose concentration between healthy roots and roots with high disease ratings within a variety were related to the severity of disease symptoms but were unrelated to the resistance level of the variety. However, the resistance level of a variety is critically important since it has a considerable impact on the frequency and severity of roots with RRCR. Research to develop sugarbeet breeding lines with enhanced genetic diversity progressed (objective 4). Three germplasm lines with unique and broadened genetic variation were released in FY14. The lines were derived from crosses between L19, a sugarbeet germplasm line noted for its ability to produce hybrids with relatively high sugar concentrations, and three previously released germplasm lines, Y318, Y319, and Y322, which were derived from a cross between cultivated sugarbeet and a wild relative of sugarbeet collected in Greece. The released lines were selected for improved sucrose concentration. Development of breeding lines with greater allelic diversity is important since the genetic base of the commercial sugarbeet crop is relatively narrow. These lines will allow breeders to incorporate additional genetic diversity into their elite populations and parental lines. Additionally, a research study was initiated to investigate mechanisms that regulate sugarbeet storage respiration rate (objective 2), and research to characterize relationships between root impurity components that decrease sucrose recovery during processing progressed (objective 3).
1. Generation of new genomic resources for sugarbeet. ARS researchers in Fargo, ND and Madison, WI generated and characterized a transcriptome from sugarbeet leaf and root tissue at varying stages of development and production and used this transcriptome to identify single sequence repeat (SSR) loci and develop SSR markers. The transcriptome, which contains 82,404 unigenes, identifies and describes functional elements of the sugarbeet genome and serves as a catalog of sugarbeet expressed genes. The 7680 SSR loci identified in the transcriptome and the 288 newly developed SSR markers provide new tools for genetic research, selective breeding, and sugarbeet germplasm improvement. The transcriptome, SSR loci, and SSR markers were made freely available to all, with no restrictions on their use, to facilitate sugarbeet physiology, pathology and genetic research, aid novel gene discovery, and promote sugarbeet crop improvement.
Fugate, K.K., Ferrareze, J.P., Bolton, M.D., Deckard, E.L., Campbell, L.G., Finger, F.L. 2013. Postharvest salicylic acid treatment reduces storage rots in water-stressed but not unstressed sugarbeet roots. Postharvest Biology and Technology. 85:162-166.
Campbell, L.G., Fugate, K.K. 2013. Divergent selection for amino-nitrogen concentration in sugarbeet roots. Journal of Sugar Beet Research. 50:1-13.
Campbell, L.G., Cattanach, A.W. 2013. The American Society of Sugar Beet Technologists advancing sugarbeet research for 75 years. Journal of Sugar Beet Research. 50:14-24.
Fugate, K.K., Fajardo, D., Schlautman, B., Ferrareze, J.P., Bolton, M.D., Campbell, L.G., Wiesman, E.C., Zalapa, J.E. 2014. Generation and characterization of a sugarbeet transcriptome and transcript-based SSR markers. The Plant Genome. 7(2) doi: 10.3835/plantgenome2013.11.0038.