Thesis (M.Sc.) -- Chulalongkorn University, 2008

The allelopatic effect of 3 tropical weeds, purple nutsedge (Cyperus rotundus L.), Indian heliotrope (Heliotropium indicum L.) and Pha-yaa mutti (Granagea maderaspatana Poir.) were studied. It was found that the dichloromethane crude extract showed higher inhibitory effect than the methanol crude extract. The dichloromethane extract of purple nutsedge at 1 g equivalent (dry weight) exhibited 86, 76 and 73% inhibitory effect on germination of giant mimosa (Mimosa pigra L.), respectively. Root growth elongation of the tested species revealed 81, 61 and 35% inhibition, respectively. In addition, shoot elongation inhibition of those plants were 62, 46 and 32%, respectively. The allelopatic effect of Indian heliotrope,purple nutsedge and Pha-yaa mutti crude extracts against crop plants (Impomoea aqutica, Brassica alboglaba, Brassica chenensis, Zea mays) and some weeds (Celosia argentea, Ruellia tuberosa, Dactyloctenium aegyptium and Chloris barbata were tested at 1 g equivalent (dry weight). D. aegyptium, C. barbata and C. argentea exhibited 100% germination inhibition activity and R. tuberosa displayed 47% germination inhibition. Furthermore, I. aqutica and Z. mays exhibited 35 and 50% germination inhibition, respectively, but B. alboglaba and B. chenensis did not show germination inhibition comparing with control.