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Submitted to: Annual Beet Sugar Development Foundation Research Report
Publication Type: Other Publication Acceptance Date: 9/15/2004 Publication Date: 12/1/2004 Citation: Smigocki, A.C. 2004. Improvement of root maggot and disease resistance in sugarbeet. Annual Beet Sugar Development Foundation Research Report. p. 3-10. Interpretive Summary: Disease and pest problems are responsible for decreases in production of sugar from sugarbeet. One of the most devastating insect pests of sugarbeet is the sugarbeet root maggot. The insect is currently found in more than half of the sugarbeet acreage in the United States and all of the Canadian fields. Chemical insecticides are the only available measure for control of the maggot. Some of these insecticides will not be available for root maggot control as they are reevaluated for safety by the Environmental Protection Agency. A strong impetus exists for development of environmentally friendly, alternative control measures for the maggot. Genetic engineering approaches hold more promise for introduction of known disease resistance traits (genes) to sugarbeet. We developed strategies that include the identification of genes or traits that may provide resistance. We identified genes that have the potential to specifically target the digestive system of the maggot thus starving the insect. We also initiated studies to identify the mechanisms that are responsible for resistance to the maggot in a sugarbeet cultivar that has been released (registered) as a moderately resistant plant. As a first step in this process, we developed a laboratory screening method for the maggot using seedlings of the resistant and susceptible plants. The maggot-damaged plant material derived by this screening method is being used to recover resistance traits. To transfer beneficial genes to commercially important sugarbeet varieties, we developed a method that delivers genes directly to sugarbeet using high velocity biolistics (gene gun). This information will be used by scientists to increase our knowledge of the mechanisms controlling plant responses to insects and lead to environmentally safe approaches for reducing the use of harmful pesticides. Technical Abstract: The sugarbeet root maggot (Tetanops myopaeformis Roder) is a major insect pest of sugarbeet in the United States and Canada, accounting for yield losses in the range of 10 to 100%. Currently no biological control measures exist and crop rotation has been ineffective due to the mobility of the adult flies and existence of several weed species as substitute hosts. A few insecticides are available but provide inconsistent results. In the last few years, we have developed a method for direct gene transfer to sugarbeet leaves that uses greenhouse grown plants and generates transgenic plants within three months. We have identified and engineered a number of beneficial genes for specific expression in sugarbeet leaves and taproots. One class of genes targets the digestive system of the maggot thus starving the insect. We identified two major classes of digestive enzymes in midguts excised from feeding maggots and demonstrated their inhibition by specific proteinase inhibitors. Genes encoding these proteinase inhibitors will be introduced into sugarbeet to evaluate their effect in planta. We have also initiated studies to profile the defense response genes in maggot resistant sugarbeet lines. As a first step, we developed an in vitro root maggot bioassay using resistant (F1016) and susceptible parental (F1010) lines to generate infested tissues as source of mRNA for preparation of differential cDNA libraries enriched for resistance genes. Clones with potential roles in root maggot and disease resistance will be characterized, reconstructed for plant expression and their role in resistance evaluated in transgenic plants. |
