THE ALLELOPATHIC EFFECT OF 3 AMARANTHUS SPP (PIGWEEDS) ON WHEAT (TRITICUM-DURUM)

The allelopathic effect of Amaranthus retroflexus L., Amaranthus blito ides S. Wats, and Amaranthus gracilis Desf. on wheat Triticum durum L. was investigated under laboratory, glasshouse and field conditions. L aboratory experiments showed that fresh shoot or root extract of the t hree weed species reduced germination, coleoptile length, root length and root dry weight of wheat seedlings. The inhibitory effects were ra te dependent, with low concentrations of shoot extract promoting shoot growth of wheat. Fresh plant extracts were more phytotoxic than dried plant extracts and shoot extracts had higher detrimental effects than root extracts. In pot experiments, dried shoot extract of A. gracilis increased shoot and root dry weights of wheat seedlings. For A, retro flexus and A. blitoides the extracts of these and dried shoots (8 g kg (-1)), which had been added to soil mixtures significantly reduced ger mination and growth of wheat seedlings. Addition of up to 16 g kg(-1) of A. gracilis residues promoted shoot growth of wheat and had no sign ificant harmful effect on root growth. Roots appeared more sensitive t o allelopathic effect than shoots. Under field conditions, incorporati on of A. retroflexus or A. blitoides residues in the soil reduced heig ht, grain and straw yield of wheat, whereas A. gracilis residues stimu lated plant height and increased yield.