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United States Department of Agriculture

Agricultural Research Service

2010 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
Sweetpotato varieties with vigorous, compact growth habits (bunch type) are more competitive against weeds than varieties with the more common viny growth habit. An ongoing project conducted in cooperation with the sweetpotato breeder at the U.S. Vegetable Laboratory is directed toward developing highly competitive sweetpotato varieties and assessing the effect of vigorous growth habit on weed interference. Twenty nine germplasm lines with vigorous bunch type canopy growth were evaluated in a field experiment to identify competitive lines with high yields and good horticultural characteristics. Clomazone is registered for use in watermelon; however, tolerance to the herbicide is marginal and the possibility of crop injury restricts its use by growers. Field and greenhouse experiments demonstrated that there are substantial differences among watermelon genotypes in clomazone tolerance. African watermelon lines belonging to the watermelon subspecies, citroides were shown to tolerate approximately five times the clomazone rate that is tolerated by commercial watermelon varieties. The citroides lines readily cross with domestic watermelon. Research was initiated in collaboration with the watermelon breeder at the U.S. Vegetable laboratory to evaluate the feasibility of transferring the tolerance observed in the wild watermelon line to commercial watermelon varieties using conventional plant breeding techniques. Studies conducted in collaboration with the U.S. Vegetable Laboratory virologist found that several perennial morningglory species are alternate host for the sweetpotato leaf curl virus, a new disease of sweetpotato. This observation demonstrates that these weeds should be removed from sweetpotato growing areas to eliminate a potential way for the virus to overwinter. A preliminary field investigation indicated that modern cabbage and broccoli varieties vary considerably in clomazone tolerance. Tolerant and susceptible varieties were discovered in both crop groups. A study evaluating the use of sudangrass-cowpea crop residue mulches for collard and kale production indicated that the while the mulch was effective for weed suppression, it also reduced the growth of the crops. Thus this practice was deemed unsuitable for cole crops production, and continued efforts will focus on mulches consisting of cowpea only.

1. Two clomazone tolerant Citrullus germplasm lines developed by researchers at the U.S. Vegetable Laboratory, Charleston, SC. Clomazone is an effective preemergence herbicide that is registered for use in watermelon; however, watermelons are often injured by the herbicide, and growers are reluctant to use it in direct contact with the crop. Wild watermelon germplasm populations with plants that are highly tolerant to clomazone were discovered in preliminary screening studies. Genetically uniform, tolerant germplasm lines were developed from individual plants by repeatedly self pollinating tolerant plants until no segregation for tolerance was observed. Seeds of the lines will be increased, and they will be released to the public. The lines may useful as a source of clomazone tolerance in watermelon breeding.

Last Modified: 3/27/2015
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