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United States Department of Agriculture

Agricultural Research Service

2007 Annual Report

1a.Objectives (from AD-416)
Investigate the role of plant growth habit and allelopathic potential on weed suppression by cole crops, sweetpotato, and watermelon, and identify vegetable crop genotypes that are competitive against weeds. Investigate the use of living and killed cover crop mulches in combination with other control measures for weed management in cole crops and sweetpotato. Select aggressive growth habit cowpea genotypes that are most suited for use as weed suppressive cover crop varieties.

1b.Approach (from AD-416)
Develop and use bioassay experiments to identify allelopathic and non-allelopathic cole crop and watermelon genotypes. Evaluate allelopathic and non-allelopathic lines in field and greenhouse experiments to assess the importance of allelopathic potential on weed suppression by the crops. Utilize bioassay guided extraction and chromatography procedures to isolate allelopathic substances for identification by collaborating chemists. Develop rapid techniques to identify allelopathic genotypes using bioassays or simple chemical analyses. Survey watermelon and sweetpotato germplasm collections and identify accessions with aggressive, weed suppressing growth habit. Assess the impact of growth habit on weed interference in greenhouse and field studies. Use the knowledge attained from studies on the effect of allelopathy and growth habit on weed suppression to develop guidelines for use by plant breeders to develop genotypes that are less susceptible to weed interference. Evaluate highly allelopathic sweetpotato lines for yellow nutsedge suppression in field and greenhouse studies. Evaluate ladino clover mulch for weed suppression in sweetpotato and cowpea-sorghum cover crop mulch for weed suppression in collard and cabbage. Compare the weed suppressing ability of several cowpea genotypes in field and greenhouse experiments in order to select those most suited for use as cover crops.

3.Progress Report
A recurrent mass selection breeding approach is being employed to produce a population of sweetpotato clones with a vigorous, bunch growth habit and acceptable horticultural characteristic. Approximately 100 seedlings selected for vigorous growth habit were evaluated for sweetpotato yield and quality in a field study. Six selections from the previous year were included with commercial varieties in a crossing block and seedling clones from the crossing block are currently being evaluated. Two years of field experimentation indicated that sweetpotato production in white clover cover crop mulch system is not practical due to difficulties in establishing stand and reduction of sweetpotato growth by the mulch. Investigation of the allelopathic potential of watermelon is discussed in the accomplishment section. Approximately 50 crucifer lines with vigorous growth that we identified in a preliminary germplasm screen were evaluated in a field experiment to select those most suitable for use as cover or green manure crops. Overall, collard and kale cultivars appeared to be most vigorous and provided superior ground cover in comparison to other species. Experiments to assess the growth rate and allelopathic potential of collard and kale lines have been initiated. The growth of cowpea lines selected for potential development as cover crop varieties was measured in a field experiment. The results indicated that several lines grew more rapidly and reached a greater final biomass than commercial varieties. This information will be used to select the lines most suitable for use as a weed suppressing cover crop. A greenhouse study to assess the effect of sweetpotato clones with high and low resin glycoside contents on yellow nutsedge growth was completed.

Watermelon genotypes vary in allelopathic potential. Differences in allelopathic potential among watermelon lines were demonstrated using a millet seedling growth bioassay, a fungal growth bioassay, and a bacterial growth bioassay. Wild watermelon lines that were inhibitory in bioassays contained much higher levels of phenolic compounds than extracts of noninhibitory commercial varieties. In a previous report, watermelon allelopathic potential was attributed to the presence of a simple phenolic compound, vanilic acid in germinating seeds; however, other compounds were found at much higher levels than vanilic acid in some of the lines we tested. The identification of inhibitory and noninhibitory genotypes will aid in understanding the biochemical mechanisms allelopathy in watermelon. This research contributes to the objectives of NP 304B, (Weed Science), Element E (Growth, Biology and Competition).

5.Significant Activities that Support Special Target Populations

6.Technology Transfer

Number of non-peer reviewed presentations and proceedings3
Number of newspaper articles and other presentations for non-science audiences1

Review Publications
Harrison Jr, H.F., Thies, J.A., Fery, R.L., Smith, J.P. 2006. Evaluation of Cowpea Genotypes for Use as a Cover Crop. HortScience. 41:1145-1148.

Last Modified: 3/30/2015
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