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Funded Project

Funding Program: Regional IPM Grants (S-RIPM)

Project Title: Breeding A Better Cover Crop: Development of Allelopathic Rye Cultivars for Use in Sustainable Production Systems

Project Directors (PDs): David A. Danehower [1] Jim Burton [2] Joseph Paul Murphy [3]

Lead State: NC Lead Organization: North Carolina State University

Research Funding: $121,824

Start Date: Jul-01-2006 End Date: Jun-30-2009

Pests Involved: weeds

Area of Emphasis: cover crops

Summary: Reducing herbicide use remains one of the greatest challenges in field crop Integrated Pest Management (IPM). Perhaps the most effective and environmentally benign IPM system for controlling weeds while reducing tillage is the use of cover crops. When cover crops are left as mulches in no-till or minimum tillage systems, they can dramatically enhance weed control for the following crop, while lessening the need for herbicide applications. In addition to reducing herbicide use, cover crops have the added benefit of trapping pesticide and nutrient runoff. In addition to these important benefits, cover crops also protect cropland soils from erosion and improve the soil by increasing soil organic matter. Two mechanisms operate in the suppression of weed growth in cover cropping systems. First, cover crop biomass shades the soil and intercepts light, physically inhibiting the germination and growth of weed seedlings. Second, mulches and the residual root systems of cover crops release natural products into the soil that suppress weed seed germination and growth through a process known as allelopathy. Surprisingly, given the widespread use of rye as a cover crop, little support has been directed towards the breeding of rye varieties specifically for use as an IPM weed suppression tool. Instead, conventional grain rye cultivars with the best available combination of biomass and allelopathic traits have been adapted for this purpose. We propose to expand a nascent breeding program to develop novel cultivars of grain rye for specific use as cover crops. A wide genetic base has already been assessed, and the best accessions selected. These selections have been crossed with Wrenns Abruzzi, a rye cultivar widely used as a cover crop in the southern U.S. due to its excellent biomass and moderately allelopathic characteristics. Further selections from the resulting breeding population will be based upon high concentrations of multiple allelopathic compounds and high biomass production. The proposed research includes analysis of allelochemical production in both shoot and root tissues in order to obtain a complete picture of the allelopathic potential of the materials and field as well as laboratory bioassay and field assessment of weed control. Objectives: We propose to continue an ongoing program to develop novel cultivars of grain rye for use as cover crops in a more effective and predictable weed management system. A wide genetic base has already been assessed, the best accessions from this base have been selected, and these selections have been crossed with Wrenns Abruzzi, a rye cultivar widely used as a cover crop in the southern U.S. due to its excellent biomass and good allelopathic characteristics. Further selections from the resulting breeding population will be based upon the concentration of multiple allelopathic compounds (benzoxazilinones, b-PLA, and/or b -HBA), late maturity, and high biomass production. We will assess the production of allelochemicals in both shoot and root tissues in order to obtain a complete picture of the allelopathic potential of the materials. Objective 1: We will evaluate a synthetic (S0) rye plant population (Synthetic 1) developed from highly allelopathic parents crossed with Wrenns Abruzzi for use as a cover crop in the southern U.S. Evaluate the following traits in selections from this population: allelochemical production of selections in both root and shoot tissues, allelopathic activity of aqueous extracts in both broadleaf and grass weed bioassays, biomass yield, and days to maturity. Objective 2 We will estimate the genetic parameters for allelopathic potential in the broad-based Synthetic 1 population (half-sib families have already been developed; seed in cold storage). In addition to evaluation of genetic parameters, we will also evaluate the allelochemical content of ashoot and root tissues at Feekes stages 7 and 10, biomass yield, and days to maturity for plants in the population.

Final Report:

Results From report submitted by the PI to USDA CRIS report system PROGRESS: 2006/07 TO 2009/06 OUTPUTS: The goal of this project is to conduct research in order to create a basis for further work in developing rye cultivars with enhanced allelopathy. Our approach has been to create a synthetic population that varies in allelopathic activity and to estimate the heritability of that trait. In support of that effort, we have developed analytical chemical, in vitro, and in vivo bioassay systems that provide estimates of the allelopathic potential of the line in a field environment. From this data, we have determined that rye allelopathy is a quantitative genetic trait with heritability similar in magnitude to that of grain yield in corn. We have also isolated standards that are being used in the quantitative analysis of rye benzoxazinones, the principal allelopathic natural products in this species. Once this data is obtained, we will determine the repeatability of each assay system (chemical and biological) and determine the best methods for following allelopathic natural product content in rye in the course of breeding for this trait. PARTICIPANTS: A. M. Brooks, Graduate Student; D. Danehower, P.I.; J. P. Murphy, Co-P.I.; J. D. Burton, Cooperator; C. Reberg-Horton, Cooperator; mike Burton, Cooperator; P. Valentine, Student Research Assistant; P. Eure, Student Research Assistant. TARGET AUDIENCES: This work will be of interest to both conventional and organic farmers. Improved weed control methods that do not rely on man-made chemicals could assist both types of farmers in avoiding or minimizing the use of herbicides while increasing soil tilth through the use of an allelopathic cover crop such as grain rye. PROJECT MODIFICATIONS: Not relevant to this project. IMPACT: 2006/07 TO 2009/06 Bioassay systems using Redroot pigweed (Amaranthus retroflexus) germination, root length and fresh weight biomass were quantified to assess variation in allelopathic activity of rye. Half-sib families were grown at two North Carolina locations and were utilized to obtain estimates of genetic variance and heritability. All measures displayed normal distributions indicating that allelopathy in rye is a quantitative trait. Genetic variation among half-sib families was significant for most measures of redroot pigweed control. Estimates of narrow sense heritability ranged from 0.17-0.21 on per plot basis and 029-0.35 on an entry mean basis. Standard errors for heritability were 0.09-0.11 on a per plot basis and ranged from 0.13-0.15 on an entry mean basis. Higher heritabilities were observed when using quantitative chemical data for benzoxazinone (BX) content. The relationship between allelopathy measured in the bioassay system and the BX content measured in the chemical analysis system was not as strong as anticipated. Based on the presence of significant variation and moderate heritabilities in both the bioassay and chemical analysis systems, it is concluded that selection for allelopathy in rye can be an effective method for improving the allelopathy of grain rye cultivars. It was also concluded that methods for assessment of allelopathic activity in rye need to be improved if this system is to be used as a basis for genetic selection. PUBLICATIONS (not previously reported): 2006/07 TO 2009/06 1. LaHovary, C., Burton, J.D., Ma, G., Danehower, D.A., Williamson, J.D. and Baerson, S. 2006. Developmental regulation of DIBOA biosynthesis in rye. Weed Science Society of America, 46th Annual Mtg, New York. Feb. 12-16, 2006. Abstracts #138. 2. Brooks, A.M., J.D. Burton, M.G. Burton, D. A. Danehower, J. P. Murphy and S.C. Reberg-Horton. Selection for Allelopathy in Rye (Secale cereale). Weed Science Society of North Carolina. Annual Meeting, Raleigh, NC, March 6, 2008. 3. Reberg-Horton, C. A. M. Brooks, D. A. Danehower, M. Burton, J. Burton, G. Ma, and P. Murphy. 2008. Breeding rye cover crops for increased allelopathic potential. Fifth World Congress on Allelopathy. Sept. 21- 25, 2008. Saratoga Springs, New York. Abstracts #219. 4. Burton, J. D., C. LaHovary, C. Sickler, D.A. Danehower, C. Reberg-Horton, M. Burton, and P. Murphy. 2008. Rye cover crop management to enhance allelopathic weed suppression. Fifth World Congress on Allelopathy. Sept.21- 25, 2008. Saratoga Springs, New York. Abstracts #177. 5. Brooks, A. M., D. A. Danehower, Reberg-Horton, C., M. Burton, J. Burton, G. Ma, and P. Murphy. 2008. Selection for allelopathy in Rye (Secale cereale). Fifth World Congress on Allelopathy. Sept. 21- 25, 2008. Saratoga Springs, New York. Abstracts #221. 6. Brooks, A. M. 2008. Allelopathy in rye (Secale cereale). M.S. Thesis, North Carolina State U. 125 pp. [electronic resource] located at: http://www.lib.ncsu.edu/theses/available/etd-10242008-090411/unrestri cted/etd.pdf. 7. Brooks, A. M., D. A. Danehower, J. P. Murphy, J. D. Burton, C. Reberg-Horton, and M. Burton. 2009. Estimation of Genetic Parameters for Rye Allelopathy (Secale cereale). In preparation.

Outcomes N/A

Impacts From report submitted by the PI to USDA CRIS report system Bioassay systems using Redroot pigweed (Amaranthus retroflexus) germination, root length and fresh weight biomass were quantified to assess variation in allelopathic activity of rye. Half-sib families were grown at two North Carolina locations and were utilized to obtain estimates of genetic variance and heritability. All measures displayed normal distributions indicating that allelopathy in rye is a quantitative trait. Genetic variation among half-sib families was significant for most measures of redroot pigweed control. Estimates of narrow sense heritability ranged from 0.17-0.21 on per plot basis and 029-0.35 on an entry mean basis. Standard errors for heritability were 0.09-0.11 on a per plot basis and ranged from 0.13-0.15 on an entry mean basis. Higher heritabilities were observed when using quantitative chemical data for benzoxazinone (BX) content. The relationship between allelopathy measured in the bioassay system and the BX content measured in the chemical analysis system was not as strong as anticipated. Based on the presence of significant variation and moderate heritabilities in both the bioassay and chemical analysis systems, it is concluded that selection for allelopathy in rye can be an effective method for improving the allelopathy of grain rye cultivars. It was also concluded that methods for assessment of allelopathic activity in rye need to be improved if this system is to be used as a basis for genetic selection

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