Differential allelopathic potential of grain sorghum genotypes to weeds

Ten sorghum genotypes were screened for their allelopathic potential against weeds. Toxicity of root exudates and residues, persistence of residues phytotoxins in soil and identification and quantification of phytotoxins were determined. All sorghum genotypes significantly inhibited the growth of Lolium temulentum weed. Of the 10 genotypes tested Giza 15, Giza 115 and Enkath were the most allelopathic cultivars with growth inhibition of 71–75% in test weed. Rabeh was least allelopathic cultivar with 56% growth reduction. Field test revealed that residues of these cultivars significantly reduced the weed numbers (59–67%) and weed growth (58–66%). Toxicity of sorghum residues persisted in soil for 10 weeks with higher rate of residues in soil. Root exudates of Giza 15, Giza 115 were found more toxic to the test companion weed Echinochloa colonum than other cultivars. Six phytotoxins (phenolic acids) were identified in the residues. Giza 15 and Giza 115 accumulated up to 5-times more p-hydroxybenzoic acid than Rabeh cultivar, while, Enkath accumulated up to 3-times more than Rabeh cultivar.