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United States Department of Agriculture

Agricultural Research Service

2008 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 was employed to produce a population of sweetpotato clones with a vigorous, bunch growth habit and acceptable horticultural characteristic. Approximately two hundred seedlings selected for vigorous growth habit were evaluated for yield and quality in an unreplicated field study. Eighteen selections from the previous year were included in a replicated field study to identify those with the best yields and horticultural traits. A field experiment was completed to determine the biofumigation potential of residues of brassica greens crops. The residues were not effective in suppressing weed growth. Evaluation of cowpea lines selected for potential development as cover crop varieties was continued, and seeds of eight genotypes were increased for a germplasm release planned for next year. A greenhouse experiment was initiated to compare the effect of allelopathic and non-allelopathic watermelon lines on weeds. Extracts of seed coats of wild watermelons were found to be highly inhibitory in seed germination and bacterial growth bioassay. A bioassay guided approach was employed to isolate allelopathic components from watermelon seed coats. Most of the seed germination and bacterial growth inhibiting potential was found in water soluble components in the seed coat extract. Annual and perennial morningglories which are closely related to sweetpotato were found to be alternate host for the sweetpotato leaf curl virus. This discovery indicates that removal of perennial morningglories from sweetpotato production areas may eliminate a source of the virus. The research was conducted in collaboration with a virologist and entomologist at the U.S. Vegetable Laboratory, and also led to the identification of over 60 new plant species that are hosts for the sweetpotato whitefly which is the vector for the sweetpotato leaf curl virus. This research contributes to National Program 304B (Weed Science) Component VII (Weed Biology and Ecology) Element E (Growth, Biololgy and Competition), Component VIII (Chemical Control of Weeds) Element A (Herbicide Use in Minor Crops) and Component X, (Weed Management in Cropland), Element A (Cultural and Mechanical Control) and Element B (Integrated Management in Cropland).

1. Sweetpotato varieties differ in tolerance to clomazone herbicide. Differences in the response of sweetpotato clones to clomazone were observed following use of the herbicide for weed control in plant beds that contained the lines of the sweetpotato breeding project at the U.S. Vegetable Laboratory. Field and greenhouse experiments were conducted to confirm this observation and quantify the level of difference in clomazone tolerance. The most tolerant lines were only slightly injured by up to eight times the rate that caused severe injury to the most susceptible lines. Important commercial sweetpotato cultivars and advanced breeding lines were tested in the greenhouse to identify those that are susceptible. Since clomazone is the most effective of the 3 preemergence herbicides currently registered for use in sweetpotato in the US, it is important that new varieties are not susceptible. The report of this research to the National Sweetpotato Research Collaborators Group in January, 2008 alerted sweetpotato breeders that testing for clomazone tolerance is needed to avoid the problem. This research contributes to the objectives of National Program 304B, (Weed Science), Component VIII (Chemical Control of Weeds) Element A (Herbicides Use in Minor Crops).

5.Significant Activities that Support Special Target Populations

6.Technology Transfer

Number of Non-Peer Reviewed Presentations and Proceedings2

Review Publications
Harrison Jr, H.F., Mitchell, T.R., Peterson, J.K., Wechter, W.P., Majetich, G.R. 2008. Caffeoylquinic Acids in Storage Roots of Sixteen Sweetpotato Genotypes. Journal American Society Hortscience. 133(4):492-500.

Harrison Jr, H.F., Levi, A., Kousik, C.S. 2008. A survey of watermelon germplasm for inhibitory seed exudates. HortScience. 42(1):138-142.

Harrison Jr, H.F., Peterson, J.K., Snook, M.E. 2008. Environment and Genotype Affect Sweetpotato Storage Root Periderm Resin Glycoside Content. HortScience. Allelopathy Journal 22(1) : 93-100.

Last Modified: 4/22/2015
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