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

Author
item LA HOVARY, CHRISTOPHER - North Carolina State University
item Baerson, Scott
item WILLIAMSON, JOHN - North Carolina State University
item DANEHOWER, DAVID - North Carolina State University
item MA, GIULAN - North Carolina State University
item Pan, Zhiqiang - Peter
item Mask, Melanie
item BURTON, JAMES - North Carolina State University

Submitted to: International Journal of Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2015
Publication Date: 1/1/2016
Citation: La Hovary, C., Baerson, S.R., Williamson, J.D., Danehower, D.A., Ma, G., Pan, Z., Mask, M.M., Burton, J.D. 2016. Phytotoxicity and benzoxazinone concentration in field grown cereal rye (Secale cereale L.). International Journal of Agronomy. 2016:1-11. doi:10.1155/2016/6463826.

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 developmental regulation. Therefore, to more effectively utilize rye as a cover crop, identification of genes involved in the synthesis of benzoxazinoid compounds, as well as an understanding of their expression levels at different developmental stages could be extremely important. This manuscript provides information on the structure of several genes potentially associated with benzoxazinoid synthesis, and examines their expression in developing rye plants. In addition, the levels of benzoxazinoids at the same developmental stages were determined. In summary, this manuscript provides information important to growers, weed scientists, and plant molecular biologists interested in maximizing the potential of rye as a weed-inhibiting cover crop.

Technical Abstract: Rye (Secale cereale L.) synthesizes benxoxazinone allelochemicals that contribute to its ability to suppress weeds. The developmental stages and physiological conditions under which rye plants synthesizes maximal levels of allelochemicals are not well defined. Knowledge of the conditions under which genes encoding benxoxazinone biosynthesis enzymes are expressed should help in determining the timing and potential for manipulation of maximal allelochemical content in rye leaf tissue. The sequences of genes encoding anthranilate synthase alpha 1 (ASA1), tryptophan synthase alpha (TSA), indole-3-glycerol phosphate lyase BX1 (Bx1) and cytochrome P450 monooxygenase BX2 (Bx2) were obtained. The rye genes were closely related to homologous genes in other Triticeae. The expression profiles of these genes were determined in individual leaves of vegetatively growing rye plants, as well as the corresponding changes in the concentration of benzoxazinones (DIBOA, DIBOA-glucoside and BOA). Maximum benzoxazinone levels were found in the youngest tissue, as were the highest expression levels for the genes Bx1 and Bx2. The genes for Bx1 and Bx2 exhibit highly similar, developmentally-correlated expression patterns, while ASA1 and TSA are expressed at a constitutive, basal level.