A CHEMICAL BASIS FOR DIFFERENTIAL ALLELOPATHIC POTENTIAL OF SORGHUM HYBRIDS ON WHEAT

The basis for differential allelopathic potentials among sorghum (Sorg hum bicolor L. Moench) hybrids was investigated by conducting quantita tive and qualitative studies of their phenolic contents. Total phenoli c content in sorghum plant parts varied within hybrids, among hybrids, and between growing seasons. Inhibition of wheat (Triticum aestivum L .) radicle growth was positively associated (r = 0.66) with concentrat ions of total phenolics contained in plant parts. Extracts from culms contributed the highest proportion of toxicity from sorghum plants, in hibiting radicle growth up to 74.7$%. Concentrations of five phenolic acids, p-hydroxybenzoic (POH), vanillic (VAN), syringic (SYR), p-couma ric (PCO), and ferulic (FER), differed in all plant parts of the three sorghum hybrids. Concentrations of POH, VAN, and SYR were consistentl y higher than PCO and FER. PCO and FER were absent from some plant par ts, with FER being the most frequently missing. Inhibition of wheat ra dicle growth was found to be positively associated with the concentrat ion of each phenolic acid. Vanillic acid was most highly associated (r = 0.44) with inhibition. Thus, above-ground sorghum tissues contained phenolic acids that contributed to allelopatic potential. Additionall y, sorghum roots exuded POH, VAN, and SYR that may enhance the overall allelopathic potential of sorghum during growth and after harvest whe n residues remain on the soil surface or are incorporated prior to pla nting a subsequent crop.