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United States Department of Agriculture

Agricultural Research Service

Research Project: Sustainable Forage-Based Production for the Mid-South Transition Zone

Location: Forage-animal Production Research

2013 Annual Report

1a. Objectives (from AD-416):
Objective 1. Improve pasture productivity and animal performance while reducing fertilizer inputs on southeastern pastures by developing optimal combinations of forage legumes and grasses including controlling and replacing toxic endophyte-infected (EI) tall fescue (TF). Subobjective 1.A. Determine if clover in mixture with common toxic endophyte (CTE) TF can dilute ergot alkaloids (EA) in the diet to mitigate the effects that FTOX (fescue toxicosis) has on animal performance and wellbeing. Subobjective 1.B. Determine the effects of CTE TF seed head suppression on EA concentrations, animal performance and recovery from toxicosis. Objective 2. Improve forage production and utilization strategies by developing and applying a better understanding of how genetic and environmental factors affect metabolites in southeastern forage grasses and legumes. Subobjective 2.A. Determine metabolite changes in forage grasses and legumes due to genetics/phenotype and/or environmental factors and determine subsequent implications for forage production and utilization. Subobjective 2.B. Identify fractions of clover extracts, or pure compounds (e.g., biochanin A) having antimicrobial activity on selected rumen bacteria. Subobjective 2.C. Develop transgenic forage legumes to alter or knock out biochemical pathways to gain a better understanding of isoflavonoid biosynthesis. Objective 3. Improve the productivity, quality and persistence of forage grasses by developing and applying a better understanding of the interactive mechanisms between endophytes, host plants and environmental factors. Subobjective 3.A. Response of novel or non-toxic endophyte (NTE) strain combinations to stress. Subobjective 3.B. Examine the effects of endophyte on survival and regrowth in different Endophyte-Infected/Endophyte-Free (E+/E-) TF clone pairs after drought stress. Subobjective 3.C. Genome-wide analysis of transcription and RiboNucleic Acid (RNA) processing in the endophyte-plant system. Objective 4. Develop guidelines for managing animal-plant-soil characteristics to improve soil quality and reduce the risks of climatic variations on southeastern pasture productivity and animal performance. Subobjective 4.A. Determine how TF genotype interacts with both fungal endophyte presence/genotype and changes in climate to alter TF production, secondary metabolite concentrations, and overall fescue forage quality. Subobjective 4.B. Legume levels in TF pastures affect carbon sequestration after renovation. Subobjective 4.C. Water soluble Phosphorus (P) losses within pastures are spatially coincident with reduced carbon (C) storage.

1b. Approach (from AD-416):
Forage systems provide low-cost feed, conserve soil and water resources, and mitigate man’s impact on the environment. Limited basic biological information exists on the cross-talk mechanism between tall fescue (TF) (the predominant forage of the transition zone) and its fungal endophyte (symbiont – beneficial to TF plant), as well as how the plant and/or fungal metabolites affect forage quality, persistence, and production. Furthermore, little is known about the impact that forage and/or fungal metabolites have on their pasture ecosystems. Gaps in our current knowledge are hindering researchers’ abilities to predict and select best combinations of forages and management systems for use by forage-animal production enterprises. Aiding researchers to develop new forage varieties, forage systems, and management recommendations for improving sustainability of forage-based enterprises will require an improved understanding of metabolite (plant and fungal) profiles and their biological functions at the molecular, cellular and organismal levels. This research project proposes to decipher the complex interactions within the animal-plant-environment interface; improve sustainability of forage-based enterprises through improved forages and forage systems management; and improve basic understanding of the plant/fungal metabolite effects on forage plant persistence and production, as well as consequent effects on the structure and function of pasture ecosystems. The objectives of the proposal are focused on the predominant forage of the transition zone, TF, as well as on its companion species (e.g., red clover).

3. Progress Report:
Scientists determined that a late-fall or early-spring applications of metsulfuron on endophyte-infected tall fescue can result in some kill of tall fescue plants and reduced seed head suppression, but a late spring application will not reduce tall fescue stands and will maximize suppression of seed heads. It was clearly demonstrated with clonal pairs of endophyte-infected and non-infected tall fescue plants that the endophyte imparts the plant with an improved tolerance to water stress. Further, genes that are expressed during moisture stress that can be attributed to the endophyte were identified. Endophyte infection and presence of legumes were determined to improve soil carbon and structure, but legumes were shown to be of greater value to improving soil properties than endophyte infection.

4. Accomplishments
1. Presence of endophyte affects tall fescue host plant physiology and enhances stress tolerance. Though endophyte infected plants have been shown to have greater adaptation under drought conditions compared to uninfected plants, this interaction varies with plant genotype and endophyte. Differences were determined in tiller recovery after 2 or 3 days of withholding water, with more tillers recovered in endophyte-infected than endophyte-free plants. There also was an endophyte effect on metabolites. These results clearly demonstrated symbiont-enhanced stress tolerances in tall fescue.

2. Presence of endophyte affects host plant gene expression under stressed (water deficit) and unstressed conditions, and across different plant tissues. Though much published research has shown endophyte effects on plant growth and performance under water deficit stress, no information is available on how endophytes affect host plant gene expression when plants are subjected to stress. Ribonucleic acid sequencing of two clone pairs of endophyte-infected and -free tall fescue plants subjected to water deficit stress was able to identify important genes that are up-regulated under stress and endophyte effects on plant gene expression in unstressed and stressed conditions. The results improved understanding about the nature of grass-endophyte interactions especially under stress conditions.

3. Soil organic matter fractions and aggregate distribution in response to tall fescue stands. It is not understood if adding a legume to endophyte-infected tall fescue can improve soil structure and carbon storage during pasture renovation to ultimately enhance nutrient cycling and water transport. Adding a legume to endophyte-infected tall fescue increases particulate organic matter carbon and nitrogen, macro- and microaggregate distribution, and the carbon associated with aggregates. Endophyte status can positively affect soil carbon and soil structure, but a potentially greater influence can be the renovation of pastures with mixtures of legumes and fescue.

Last Modified: 05/26/2017
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