Allelopathic effects of Hulless barley (Hordeum vulgare L.) on rape (Brassica campestris L.)

Hulless barley (Hordeum vulgare L.) is alpine crop grown only in the Qinghai-Tibetan Plateau. The allelopathic effects of its 66-varieties were evaluated on rape by the relay-seeding coculture in agar and in Pot culture. Two varieties (Qing 0039 and Qing 0415) significantly inhibited the root length (66.67% and 71.81%, respectively) in Brassica campestris L. The results of Response index (RI) values were similar to the relay-seeding co-culture in agar test. The leachates of its 5-varities (Tibet 1295, Qing 0079, Qing 0373, Tibet 0921 and Qing 0230) inhibited the rape seedlings growth. Their inhibition was drastic (100% inhibition) in root length and shoot length but was less (< 80% inhibition) on dry weight. In Cluster analysis, varieties in Group 1 (Qing 0415 and Qing 0039) were inhibitory to root length and dry weight of rape. In the relay-seeding co-culture in agar and leachate experiments the variety Qing 0039 proved most allelopathic. Its roots significantly inhibited the rape seedlings growth up to 5-7 cm distance. The extracts from its whole plants contained 9 compounds (tricin 4'-O-(threo-beta-guaiacylglyceryl) ether (I), tricin 4 '-O-(erythro-beta- guaiacylglyceryl) ether (II), salcolin C (III), methyl ferulate (IV), dibutylphthalate (V), (+)syringaresinol (VI), (+)-(7R, 7 ' R, 7 '' S, 7 ''' S, 8S, 8 ' S, 8 '' S, 8 ''' S)-4 '', 4 '''-dihydroxy-3, 3 ', 3 '', 3 ''', 5, 5 '-hexamethoxy- 7, 9 '; 7 ', 9-diepoxy-4, 8 ''; 4 ', 8 '''-bisoxy-8, 8 '-dineolignan-7 '', 7 ''', 9 '', 9 ''''-tetraol (VII), tricin (VIII) and chlorogenic acid (IX)), in which compounds I, II and V were most allelopathic.