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United States Department of Agriculture

Agricultural Research Service


Location: Forage Seed and Cereal Research

2013 Annual Report

1a. Objectives (from AD-416):
Provide the seed industry with improved grass germplasm and management practices that reduce the impact of salinity, weeds, and diseases on seed quality and profitability. Identify bioactive compounds and genes that mediate the response of Lolium and Festuca to salinity related stress. Develop approaches to characterize, select and utilize components of host genetic resistance to pathotypes of the stem rust pathogen in Lolium. Determine whether a small molecular weight bioherbicide, produced by selected naturally occurring soil rhizobacteria (Pseudomonas sp.), that inhibits the germination of Poa annua can reduce the impact of this weed on seed production and turf quality. Develop molecular methods and tools that facilitate germplasm improvement for diverse uses. Develop a means to improve gene stability and minimize escape of transgenes in forage and turf grasses (Lolium sp.). Characterize genetics of host resistance to stem rust, and develop molecular markers for stem rust resistance in Lolium. Identify candidate genes that can be exploited to increase biomass of cool-season grass plants (Lolium sp.) to improve forage quality and source material for bioenergy production.

1b. Approach (from AD-416):
Conduct complex basic and applied research to improve the production and utilization of seed and grain from forage and turf seed cropping systems which include wheat. Traditional breeding and molecular genetics will be used to identify the genetic basis for stem rust resistance, factors that impact seed quality, flowering, and abiotic stress tolerance. Develop molecular and traditional approaches useful for altering plant developmental pathways and plant structures, and enhancing forage quality in end-use environments that differ from the seed-producing region. Bioherbicides that reduce weed presence in seed production and turf environments will be identified and characterized to enable commercialization of new products.

3. Progress Report:
This is the final report for this project which was replaced by 5358-21000-045-00D, "Improvement of Biotic and Abiotic Stress Tolerance in Cool Season Grasses". Effective weed control is a critical need in agricultural production systems. ARS scientists in Corvallis and Oregon State University collaborators discovered and characterized a naturally occurring bioherbicide produced by the soil bacterium Pseudomonas fluorescens. This bioherbicide, Germination Arrest Factor (GAF), was found to irreversibly arrest the germination of seeds of grassy weeds, such as annual bluegrass (Poa annua), without significantly affecting the growth of established grass seedlings and mature plants or germination of the seeds of broadleaf plant species (dicots). GAF was also found to inhibit the growth of a bacterium that causes fire blight in apples and pears, demonstrating that GAF has broader utility than a bioherbicide, and has potential utility as a biological control agent for this disease. Furthermore, the genetic regions responsible for the biosynthesis of GAF were identified, an important step in developing methods to produce commercially significant quantities of the bioherbicide. Foundational research was conducted by ARS scientists in Corvallis, Oregon, to develop molecular tools and methods to study abiotic stresses in forage and turf related grasses. Reference genes were identified and developed specifically for accurately quantifying gene expression levels in Lolium, throughout plant development and during exposure to various abiotic stresses. To study the role genes play in abiotic stress tolerance, plant transformation methods were established for model grass species Brachypodium and Lolium. Currently molecular information on genes involved in salinity stress in forage and turf related grasses is limited, we identified 6800 distinct genes or gene families that were expressed in Lolium plants while under-going salinity stress. Screening different accessions of the model grass Lolium temulentum resulted in the identification of germplasm with different degrees of salt tolerance. In order to improve the plants ability to respond to stress, it is critical we understand how a plant recognizes their environment. Our research identified signaling and regulatory components involved in perception and mediation of different abiotic stresses in forage related grasses. Genetic resistance to disease is the best long-term approach to managing stem rust. Stem rust is the most significant disease problem for seed production crops of perennial ryegrass and tall fescue. ARS scientists in Corvallis, Oregon, discovered a source of genetic resistance to the stem rust pathogen in perennial ryegrass. These researchers also identified genetic variants of the fungus that causes stem rust disease of ryegrass, which differ in their disease-causing ability. ARS scientists identified the regions of 3 ryegrass chromosomes which carry resistance to a mixed population of the stem rust pathogen. In addition, these ARS researchers were the first to demonstrate the utility of molecular marker systems originally develop for animal systems for mapping in a forage grass.

4. Accomplishments
1. Antibiotic production by a soil bacterium inhibits the growth of certain plant pathogens. Strain SBW25 of the bacterium, Pseudomonas fluorescens has been extensively studied for its plant growth promoting properties and its ability to protect certain crops from disease. The basis of this protection was not understood and the disease reducing properties could not be extensively applied to crop production. ARS scientists at Corvallis, Oregon, and Oregon State University scientists, isolated and identified the antibiotic, L-furanomycin from cultures of this bacterium and demonstrated that this antibiotic inhibited the growth of a pathogen of tomatoes, and the bacterium that causes bacterial soft rot of corn. This research may have practical utility in crop protection and suggests that antibiotic production by SBW25 impacts the interaction of microbial populations that affect soil productivity by reducing the populations of certain crop pathogens. This is the first report of furanomycin production by a Pseudomonas bacterium.

2. Genetic regions in a soil bacterium involved in bioherbicide production. Previous work identified naturally occurring Pseudomonas fluorescens soil bacteria which produce a bioherbicide that arrests the germination of a wide range of grassy weeds that impact crop production as well as professional and recreational turfs. There is interest in developing an approach to produce commercial quantities of this naturally occurring product, but the chemical synthesis of this Germination Arrest Factor (GAF) has proven quite difficult. In order to develop an alternative approach for large scale production of GAF by viable bacteria, ARS scientists in Corvallis, Oregon, created mutants of GAF-producing bacteria to identify specific genes that are critical for GAF production and which might be enhanced to increase production of the bioherbicide. Analyses of these mutants enabled the identification of four distinct genetic regions of the bacterial genome that are involved in GAF production. This research established the basis for subsequent work to develop new strains of the bacterium that produce much greater quantities of GAF.

3. Virus Induced Gene Silencing in the model grass species Lolium temulentum. Development of stable transgenic grass plants to assess gene function can be difficult and time consuming especially in grasses. ARS scientists in Corvallis, Oregon, have developed a method to transiently reduce or shutdown gene expression in the model grass species Lolium temulentum. A plant virus delivery system was used. The development of this gene silencing system provides an initial screening method for the identification and evaluation of candidate genes that will have the potential to improve stress tolerance in forage and turf grasses.

Review Publications
Gent, D.H., Ocamb, C.M., Farnsworth, J.L. 2010. Forecasting and management of hop downy mildew. Plant Disease. 94:425-431.

Pfender, W.F., Slabaugh, M. 2013. Pathotype-specific QTL for stem rust resistance in Lolium perenne. Theoretical and Applied Genetics. 126:1213-1225.

Halgren, A., Maselko, M.B., Azevedo, M.D., Mills, D., Armstrong, D.J., Banowetz, G.M. 2013. Genetics of Germination-Arrest Factor (GAF) production by Pseudomonas fluorescens WH6: Identification of a gene cluster essential for GAF biosynthesis.. Microbiology. 159:36-45.

Last Modified: 05/25/2017
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