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

The basis for differential allelopathic potentials among sorghum (Sorghum bicolor L. Moench) hybrids was investigated by conducting quantitative and qualitative studies of their phenolic contents. Total phenolic 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 concentrations of total phenolics contained in plant parts. Extracts from culms contributed the highest proportion of toxicity from sorghum plants, inhibiting radicle growth up to 74.7$%. Concentrations of five phenolic acids, p-hydroxybenzoic (POH), vanillic (VAN), syringic (SYR), p-coumaric (PCO), and ferulic (FER), differed in all plant parts of the three sorghum hybrids. Concentrations of POH, VAN, and SYR were consistently higher than PCO and FER. PCO and FER were absent from some plant parts, with FER being the most frequently missing. Inhibition of wheat radicle growth was found to be positively associated with the concentration 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. Additionally, sorghum roots exuded POH, VAN, and SYR that may enhance the overall allelopathic potential of sorghum during growth and after harvest when residues remain on the soil surface or are incorporated prior to planting a subsequent crop.