The 2012 ASHS Annual Conference

Crotalaria juncea L. (sunn hemp) is a leguminous fiber crop that has shown excellent potential for use as a summer cover crop and green manure.  Because of its prolific biomass production, sunn hemp readily suppresses weeds in situ as a cover crop, as well as when shoot residue is retained as organic mulch.  We have previously reported on the allelopathic potential of water-soluble extracts and dried residues of sunn hemp shoots of a single commercially available sunn hemp cultivar.   Because we had access to a number of sunn hemp accessions collected from various parts of the world, a study was designed with the objective of characterizing the nature and properties of allelochemicals in sunn hemp accessions.  Bioassays for radicle growth inhibition were conducted with water eluates from thinly sliced leaves, stems and seeds and all three tissues were demonstrated to contain the inhibitory potential.  All of the 14 sunn hemp accessions originating from the United States, India, Brazil, South Africa, Pakistan, and Nigeria were found to have water-soluble allelochemicals in leaves, suggesting that the presence of allelochemicals is widely distributed in this species. The highest level of inhibitory potential was found in accession IN-86 from India.  Further characterization of IN-86 leaf eluate indicated that the inhibitory compound(s) was/were not soluble in chloroform, stable when boiled for 10 minutes, and resistant to 1 N HCl.  Binding and elution from AG1(OH^-) ion exchange resin also were observed.  HPLC/MS analysis of leaf eluates of IN-86 showed the presence of a compound with an m/z of 148, consistent with the spectrum for hydroxynorleucine, a phytotoxic non-protein amino acid previously reported in seeds of C. juncea.  We suggest that development of weed control strategies using allelochemicals derived from biomass of select sunn hemp genotypes may be feasible.