AUTOTOXICITY OF BARLEY Moncef Ben-Hammouda, 1 Habib Ghorbal, 2 Robert J. Kremer, 3, * and Oussama Oueslatt 2 1 Ecole Superieure d’Agriculture du Kef, Kef, Tunisia 2 Faculte ´ des Sciences de Tunis, Tunis, Tunisia 3 Agricultural Research Service, U.S. Department of Agriculture and Department of Soil & Atmospheric Sciences, University of Missouri, Columbia, MO 65211 ABSTRACT Allelopathic potential of a crop species varies depending on stage of growth. Because allelopathy of barley (Hordeum vulgare L.), an important cereal grain adapted to semi-arid con- ditions of northern Tunisia, has not been widely reported, a study was conducted to determine i) the potential autotoxicity of barley and ii) the differential allelopathic potential of barley plant components over four phenological stages. The study involved experiments with barley seed germination and seedling growth bioassay techniques for detection of allelopathic activity. Plant parts of field-grown ‘Rihane’ barley were extracted with distilled water. At growth stage 4 (stems not well developed), whole plants were extracted. Thereafter, roots, stems, and leaves were extracted separately. Water extracts of ‘Rihane’ barley plant parts were bioassayed on four varieties of barley. Seedling growth bioassays revealed autotoxicity of barley, which appeared JOURNAL OF PLANT NUTRITION, 25(6), 1155–1161 (2002) 1155 Copyright # 2002 by Marcel Dekker, Inc. www.dekker.com *Corresponding author. E-mail: kremerr@missouri.edu