Sorghum Allelopathy'From Ecosystem to Molecule

Sorghum allelopathy has been reported in a seriesof field experiments following sorghum establishment. Inrecent years, sorghum phytotoxicity and allelopathic interferencealso have been well-described in greenhouse andlaboratory settings. Observations of allelopathy have occurredin diverse locations and with various sorghum plantparts. Phytotoxicity has been reported when sorghum wasincorporated into the soil as a green manure, when residuesremained on the soil surface in reduced tillage settings, orwhen sorghum was cultivated as a crop in managed fields.Allelochemicals present in sorghum tissues have varied withplant part, age, and cultivar evaluated. A diverse group ofsorghum allelochemicals, including numerous phenolics, acyanogenic glycoside (dhurrin), and a hydrophobic p-benzoquinone(sorgoleone) have been isolated and identified inrecent years from sorghum shoots, roots, and root exudates,as our capacity to analyze and identify complex secondaryproducts in trace quantities in the plant and in the soilrhizosphere has improved. These allelochemicals, particularlysorgoleone, have been widely investigated in terms oftheir mode(s) of action, specific activity and selectivity,release into the rhizosphere, and uptake and translocationinto sensitive indicator species. Both genetics and environmenthave been shown to influence sorgoleone productionand expression of genes involved in sorgoleone biosynthesis.In the soil rhizosphere, sorgoleone is released continuously by living root hairs where it accumulates insignificant concentrations around its roots. Further experimentationdesigned to study the regulation of sorgoleoneproduction by living sorghum root hairs may result in increasedcapacity to utilize sorghum cover crops more effectivelyfor suppression of germinating weed seedlings, in amanner similar to that of soil-applied preemergent herbicideslike trifluralin.