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Title: Phytotoxicity and benzoxazinone concentration in field grown cereal rye (Secale cereale L.)

item LA HOVARY, CHRISTOPHER - North Carolina State University
item DANEHOWER, DAVID - North Carolina State University
item MA, GUOYING - North Carolina State University
item REBERG-HORTON, CHRIS - North Carolina State University
item WILLIAMSON, JOHN - North Carolina State University
item Baerson, Scott
item BURTON, JAMES - North Carolina State University

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2015
Publication Date: 2/5/2016
Citation: La Hovary, C., Danehower, D.A., Ma, G., Reberg-Horton, C., Williamson, J.D., Baerson, S.R., Burton, J.D. 2016. Phytotoxicity and benzoxazinone concentration in field grown cereal rye (Secale cereale L.). Journal of Agricultural and Food Chemistry. 2016 11p:

Interpretive Summary: The rye plant is often used in agricultural systems as a cover crop, and is thought to reduce the extent of weed infestions at least in part through the release of allelochemicals into the soil. Such allelochemicals are naturally occurring plant growth inhibitors, and therefore rye plantings can to some extent reduce the requirement for synthetic herbicides. One class of allelochemicals produced by rye are the benzoxazinoid compounds (DIBOA, DIBOA-glycoside and BOA), which are highly phytotoxic, and are thought to play a significant role in the weed-fighting properties of this plant. Unlike the application of synthetic pesticides to crops, the effectiveness of cover crop-based weed supression is contingent upon the levels of natural plant growth inhibitors present within the cover crop, which are in turn subject to regulation by various environmental as well as genetic factors. Therefore, to more effectively utilize rye as a cover crop, an understanding of some of the seasonal variation, as well as variation among different rye varieties with respect to benzoxazinoid levels could be extremely important. This manuscript provides information on the benzoxazinoid content at different times during the growing season for rye plants, and also compares these levels in different commonly-used rye varieties. In addition, variation in the ability to suppress weed growth are assesed using extracts prepared from various rye samples using a laboratory-based assay. In summary, this manuscript provides information important to growers and weed scientists interested in maximizing the potential of rye as a weed-inhibiting cover crop.

Technical Abstract: Winter rye (Secale cereale L.) is often used as a cover crop because of the weed suppression potential of its mulch. This research was conducted to elucidate the changes in benzoxazinone allelochemical levels in rye shoot tissue during the growing season in North Carolina. Four different rye varieties, two winter and two facultative types were planted in the fall, and 0.5 m2 plots were harvested at intervals the following spring. Two different measures of allelochemical content were taken. Seed germination bioassays were used as a general estimate of rye allelopathic potential. Dilutions of aqueous extracts from rye tissue were tested using perennial ryegrass (Lolium perenne) and pigweed (Amaranthus retroflexus) as indicator species to compare the relative toxicity of tissues harvested at different times during the season. Levels of benzoxazinones (BX) (DIBOA, DIBOA-glycoside and BOA) in rye shoot tissue were also directly determined using a GC method. We found that the allelochemical content of rye shoot tissue was generally greater early in the season, and decreased over time. Pigweed seed germination and root elongation were more sensitive to rye extracts than was ryegrass. Rye tissue from the March harvests was the most toxic to both pigweed and ryegrass, and the toxicity decreased over time. The total BX content of the tissue increased from February to March and then decreased over time. Thus, BX levels and phytotoxicity as measured by the bioassay have a similar, although not identical temporal profile. Though the BX content of the tissue decreased, the overall amount of BX.ha-1 increased because of the increase in biomass. Maximum BX “rates” of 3 to 5 kg.ha-1 were found.