2011 Annual Report
1a.Objectives (from AD-416)
Four research objectives will be undertaken in this bridging project. Objective 1: Determine the roles, internal regulation, and the environmental responses of sucrose synthase, the predominant sucrolytic activity in sugarbeet root, in carbon partitioning to the root, sucrose utilization, sucrose yield, and sucrose retention during storage. Objective 2: Determine mechanisms of respiratory control and describe the endogenous processes and interactions with pathogens that affect sugarbeet root respiration rate during storage. Objective 3: Determine the inheritance and interrelationships among traits related to sucrose yield and extractability. Objective 4: Increase genetic diversity of the commercial sugarbeet crop by identifying and incorporating novel sources of pest resistance and crossing adapted sugarbeet lines with wild relatives of sugarbeet and selecting progeny for traits related to sucrose yield and sucrose extractability.
1b.Approach (from AD-416)
The goal of the proposed research is to increase the yield of extractable sucrose from the domestic sugarbeet crop through a fundamental understanding of the genetics and physiology of sugarbeet primary carbon metabolism. The research seeks to define and characterize the cognate genetic and physiological factors that influence sucrose accumulation, retention, and recovery during production, storage, and processing of the sugarbeet crop. In addition, research will introduce valuable genetic diversity into sugarbeet breeding germplasm through crossing adapted lines with wild relatives with novel traits.
Research to understand the role of the sucrose-degrading enzyme, sucrose synthase, in sugarbeet root sucrose accumulation and retention progressed. Although sucrose synthase has been suggested to function in phloem unloading and stress responses in other plants, research conducted under this project established that the enzyme is unlikely to serve these functions in sugarbeet root. In FY11, a phenotypic, biochemical, and molecular analysis of plants with altered sucrose synthase expression indicated that the enzyme is essential for normal taproot growth, contributes to cell wall biosynthesis, and may have a role in sucrose partitioning between the sugarbeet taproot and leaves. Research to determine the metabolic factors that regulate sugarbeet root respiration also progressed in FY11. Previous research demonstrated that neither cellular energy status nor respiratory capacity limit respiration in stored sugarbeet roots, suggesting that storage respiration rate is restricted by the availability of one or more respiratory substrates. A metabolic profile of respiratory pathway substrates and intermediates in roots with different respiration rates identified an association between root respiration rate and cellular redox status. The robustness of this relationship under different experimental parameters is currently being investigated. Research to quantify the effect of production diseases on sugarbeet storage properties also continued. Previous research established that Aphanomyces root rot, rhizomania, and Fusarium yellows negatively affect sugarbeet root storage properties. In FY11, results from the first year of a multiyear study indicated that Rhizoctonia root and crown rot also has a substantial negative impact on postharvest root storage properties. Selective breeding conducted under this research project produced a germplasm line with resistance to sugarbeet root maggot. This line is now available for distribution to the public and will facilitate the incorporation of maggot resistance into commercial hybrids. This release is important since sugarbeet root maggot is the most destructive insect pest of sugarbeet in North America. In addition to being the most resistant root maggot line available, the line is moderately resistant to Cercospora leaf spot, a wide-spread fungal disease of sugarbeet. Breeding efforts also have produced lines with low concentrations of some naturally occurring substances in sugarbeet that impede sucrose recovery during normal factory operations. Three lines are being increased with the intent to release. Reduced levels of these compounds will increase payments to growers and factory efficiency. When these lines become available, they will bring the number of germplasm lines released over the life of this project to eleven.
Efficient sucrose extraction from sugarbeet. Sodium, potassium, and amino-nitrogen are naturally occurring substances that accumulate in sugarbeet roots and impede sucrose recovery during normal processing. ARS researchers in Fargo, ND, developed cultivars with substantially reduced levels of each of these substances after numerous plant breeding cycles in conjunction with chemical analysis of individual roots. They conducted yield trials that confirmed that the new cultivars consistently have lower levels of these substances than unselected populations or commercial hybrids. Seed of the three lines is being increased for release and distribution to the public. These lines will provide germplasm for future improvement in sugarbeet processing quality, thereby increasing payments to growers and improving factory efficiency.
Campbell, L.G., Fugate, K.K., Niehaus, W.S. 2011. Fusarium yellows affects postharvest respiration rate, sucrose concentration, and invert sugar in sugarbeet. Journal of Sugar Beet Research. 48:17-39.
Campbell, L.G., Panella, L.W., Smigocki, A.C. 2011. Registration of F1024 sugarbeet germplasm with resistance to sugarbeet root maggot. Journal of Plant Registrations. 5(2):241-247.
Lafta, A.M., Fugate, K.K. 2011. Metabolic profile of wound-induced changes in primary carbon metabolism in sugarbeet root. Phytochemistry. 72:476-489.