2006 Annual Report
Vegetable production in the Southeast is severely limited by the lack of adequate weed control. Weed problems are exacerbated by the warm, moist growing season and the mild winters which encourage vigorous weed growth and allow ample opportunity for reproduction. Although agrochemical and seed companies invest heavily in pest control research for major crops, little research is directed toward low acreage minor crops, a category that includes most vegetables. Land grant universities have also de-emphasized applied research on minor crops and shifted funding into molecular biology and other more basic areas of research. These factors combined with the removal from the market of herbicides and methyl bromide due to regulation or declining sales necessitates the development of alternative weed control technologies in order to sustain vegetable production. These problems are more severe in organic production where the use of synthetic herbicides is prohibited. The lack of adequate weed control is the most important obstacle to the adoption of organic or sustainable cultural practices for most vegetables.
Objective 1 of this project assesses the feasibility of manipulating two characteristics that affect inter-specific competition between plants, growth habit and allelopathy, through conventional plant breeding. The role of sweetpotato and watermelon growth habit on crop response to weed interference and weed suppression by the crops is being investigated. Cole crop and watermelon cultivars, breeding lines, and accessions varying in allelopathic potential are being evaluated in field, greenhouse and laboratory experiments to assess their impact on weed growth during crop growth and on weeds and other pests in subsequent rotational crops. The latter stages of these investigations will focus on describing selection criteria to assist plant breeders in developing competitive varieties, and highly competitive, weed suppressive lines will be released for use by plant breeders. The following research is being conducted under objective 2: Weed suppressive cowpea genotypes are being evaluated in field studies to identify those most effective in suppressing weeds. Organic mulches made from residues of ladino clover cover crop are being assessed for weed management in sweetpotato. Mulches made from residues of sorghum and cowpea cover crops are being assessed for production of fall transplanted cole crops. Allelopathic sweetpotato clones are evaluated for their ability to reduce yellow nutsedge tuber formation.
Successful completion of this research will benefit vegetable growers and the public by reducing the impact of weeds on vegetable crop production, help ensure a continued supply of affordable fresh vegetables, and reduce the impact of agriculture on the environment. Understanding the effect of vegetable crop characteristics on weed interference will provide plant breeders and other scientists with the information needed to select crop genotypes that are less vulnerable to losses due to weeds. Developing effective biologically based weed management strategies will facilitate the adoption of sustainable or organic agricultural practices in the southeastern US.
2. Initiate greenhouse and field experiments to test allelopathy and biofumigation potential of low and high glucosinolate cole crop genotypes.
3. Select competitive sweetpotato and watermelon lines from germplasm collections.
4. Initiate screening experiments to identify differences in watermelon allelopathy and growth habit.
5. Assess cover crop mulches for sweetpotato and cole crops, evaluate cowpea lines for use as a cover crop, assess impact of allelopathic sweetpotato on yellow nutsedge.
Year 2 (FY 2007) 1. Continue sweetpotato and cowpea canopy architecture/weed interference experiments.
2. Continue assessment of role of glucosinolate levels in cole crops on weeds.
3. Complete watermelon screening experiments.
4. Repeat cover crop mulch experiments and cowpea evaluation and sweetpotato allelopathy experiments.
Year 3 (FY 2008) 1. Publish results of sweetpotato growth habit/weed interference studies.
2. Develop descriptors for competitive sweetpotatoes.
3. Initiate glucosinolate analysis of Brassica oleracea core germplasm collection. Complete greenhouse and field allelopathy and biofumigation experiments.
4. Initiate greenhouse and field experiments assessing impact of watermelon allelopathy and growth habit on weeds.
5. Publish data on watermelon germplasm evaluation. Publish results of sweetpotato cover crop mulch experiments.
Year 4 (FY 2009) 1. Develop descriptors for competitive cowpea and sweetpotato genotypes.
2. Continue core collection analysis. Publish allelopathy/biofumigation results.
3. Complete greenhouse and field experiments assessing impact of watermelon allelopathy and growth habit on weeds.
4. Publish results of collard cover crop mulch research.
Year 5 (FY 2010) 1. Publish descriptors, release to public competitive sweetpotato breeding lines and cover crop cowpea breeding lines.
2. Complete core collection analysis, publish data and enter into GRIN system.
3. Publish greenhouse and field experiments assessing impact of watermelon allelopathy and growth habit on weeds.
4. Complete and publish research assessing effect of allelopathic sweetpotato varieties on yellow nutsedge.
Since FY 2006 was the first full year of the project (start date June 6, 2005), the major accomplishment for FY 2006 and the life of the project are the same. Six cowpea genotypes that have superior characteristics for use as a cover crop were identified in 2006. Of 57 lines included in a preliminary screening experiment, 6 were selected for development as cover crop genotypes. The selections were made following field evaluation at the U.S. Vegetable Laboratory over six years. The genotypes were selected on the basis of their vigorous growth habit, weed suppressing ability, indeterminate growth habit, and resistance to Southern Root Knot Nematode and environmental stress. Several have characteristics that make them superior to the standard cover crop variety, Iron Clay. This information was published in a HortScience article. Following seed increase from single plant selections, the lines will be made available to customers through a USDA germplasm release. This will ultimately provide farmers who utilize cover crops and researchers who are studying cultural practices using cover crops with cowpea genotypes that are superior to cultivars currently available from seed suppliers.
Presented and oral presentation “Evaluation of cowpea genotypes for use as a weed suppressing cover crop” at the annual conference of the American Society of Horticultural Science, New Orleans, LA, June 29, 2006.Peterson, J.K., Harrison Jr, H.F., Snook, M.E., Jackson, D.M. 2005. Content of chlorogenic acid in sweetpotato germplasm and possible roles in disease and pest resistance. Allelopathy Journal. 16:239-250.
Harrison Jr, H.F., Thies, J.A., Fery, R.L., Smith, J.P. 2006. Assessment of cowpea genotypes for use as a weed-suppressing cover crop. HortScience. 41:991.
Harrison Jr, H.F., Peterson, J.K., Snook, M.E. 2006. Monogalactosyl-diglyceride contents in sweetpotato clones. HortScience. 41:1046.
Harrison Jr, H.F., Peterson, J.K., Snook, M.E. 2006. Simulated drought induces high periderm caffeic acid contents in storage root periderm of greenhouse grown sweetpotatoes. HortScience. 41:277-278.