Allelopathic Effects of Cultivated Sunflower on Grain Sorghum

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Abstract
Greenhouse studies demonstrated the allelopathic effects of sunflower cultivar H. annuus L. ''Interstate 894'' on the growth and water status of grain sorghum, S. bicolor Moench. Significant growth reductions in sorghum seedlings were found from additions of sunflower aqueous-leaf extracts at concentrations as low as 1 g fresh weight in 120 ml nutrient solution. Reductions in sorghum growth were accompanied by decreases in leaf water potential and/or increases in diffusive resistance. Incorporation of dried sunflower leaf material into soil in which sorghum seedlings were germinated and grown caused significant depression in growth over the 2-wk test period with additions of 2 g residue to 80 g soil. Allelochemicals released from sunflower plants and residue are suggested as a possible explanation for yield reductions in crops which follow sunflower plantings. One mechanism of toxic action on seedlings involves an interference with water balance.