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Title: Sorghum allelopathy – from ecosystem to molecule

item WESTON, LESLIE - Charles Stuart University
item ALSAADAWI, IBRAHIM - University Of Baghdad
item Baerson, Scott

Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/21/2013
Publication Date: 2/8/2013
Citation: Weston, L.A., Alsaadawi, I.S., Baerson, S.R. 2013. Sorghum allelopathy – from ecosystem to molecule. Journal of Chemical Ecology. 39:142-153.

Interpretive Summary: The sorghum plant produces several growth inhibitory compounds which are secreted into the soil by root hair cells that cover the majority of the root system's surface. Sorgoleone represents one such compound, and its ability to inhibit weeds has been extensively investigated in both greenhouse and field studies. Such compounds are referred to as allelochemicals, which are thought to act as a form of chemical defense used by plants to fend off competition for limited resources in their immediate environment. The biological activity of sorghum can potentially be harnessed in several ways, all of which are discussed in detail. Work on the sorgoleone biosynthetic pathway has also led to the identification of genes involved in its biosynthesis, thus providing the necessary tools for exploring potential biotechnological applications in crops.

Technical Abstract: Sorghum allelopathy has been reported in a series of field experiments following sorghum establishment. In recent years, sorghum phytotoxicity and allelopathic interference have also been well-described in greenhouse and laboratory settings. Observations of allelopathy have occurred in diverse locations and with various sorghum plant parts. Phytotoxicity has been reported when sorghum was incorporated into the soil as a green manure, when residues have remained on the soil surface in reduced tillage settings, or when sorghum was cultivated as a crop in managed fields.Allelochemicals present in sorghum tissues have varied with plant part, age and cultivar evaluated. A diverse group of sorghum allelochemicals, including numerous phenolics, a cyanogenic glycoside (dhurrin) and a hydrophobic p-benzoquinone (sorgoleone) were isolated and identified in recent years from sorghum shoots, roots, and root exudates, as our capacity to analyze and identify complex secondary products in trace quantities in the plant and in the soil rhizosphere has improved. These allelochemicals, particularly sorgoleone, have been widely investigated in terms of their mode(s) of action, specific activity and selectivity, release into the rhizosphere and uptake and translocation into sensitive indicator species. Both genetics and environment were shown to influence sorgoleone production and expression of genes involved in sorgoleone biosynthesis. In the soil rhizosphere, sorgoleone was released continuously by living root hairs where it accumulated in significant concentrations around its roots. Further experimentation designed to study the regulation of sorgoleone production by living sorghum root hairs may result in increased capacity to utilize sorghum cover crops more effectively for suppression of germinating weed seedlings, in a manner similar to that of soil-applied preemergent herbicides like trifluralin.