SHORT REPORT Allelopathic potential of cucumber (Cucumis sativus) on barnyardgrass (Echinochloa crus-galli) HO LE THI, 1 PHAM THI PHUONG LAN, 2 DUONG VAN CHIN 2 and HISASHI KATO-NOGUCHI 1 * 1 Department of Applied Biological Science, Faculty of Agriculture, Kagawa University, Kagawa, Japan and 2 Cuu Long Delta Rice Research Institute, Cantho,Vietnam Keywords: allelopathy, Cucumis sativus, Echinochloa crus-galli, weed management. INTRODUCTION Rice is the most important crop inVietnam, while barn- yardgrass (Echinochloa crus-galli L. Beauv.) is the most significant biological constraint to rice production. In spite of the wide use of commercial herbicides to control barnyardgrass, the rice crop yield loss from this weed remains high.The negative impacts of commercial her- bicide use in relation to environmental contamination make it necessary to diversify the weed management options (Putnam 1988; Weston 1996; Einhellig 1999). Controlling weeds through allelopathy is one of the strategies to reduce commercial herbicide dependency (Rice 1984; Putnam 1988; Duke et al. 2000). It has been observed that many plant species can provide excellent weed suppression after the incorporation of their resi- dues into the soil (Semidey 1999; Caamal-Maldonado et al. 2001). However, inVietnam there has been, so far, no attempt to exploit the allelopathy of plants for pos- sible weed control purposes in the agricultural field setting. Cucumber (Cucumis sativus L.) is also one of the major crops in Vietnam. After harvesting, the plant parts of cucumber (stems, leaves, and roots) are mostly discarded. Cucumber plants have been reported to possess allelo- pathic potential by exuding allelochemicals from their roots (Putnam & Duke 1974;Yu & Matsui 1994;Yu et al. 2003).Therefore, it is of interest to assess the allelopathic potential of cucumber plants for possible weed control purposes. The present research was carried out at the Cuu Long Delta Rice Research Institute (CLRRI), Vietnam, to determine the allelopathic potential of a local cucumber variety on the germination and growth of barnyardgrass under laboratory and greenhouse conditions. MATERIALS AND METHODS Plant materials Cucumber (C. sativus L. cv. Phung Tuong) plants (including the stems, leaves, and roots, but excluding the flowers and fruit) were obtained from the field after the final crop harvest and dried at 50°C for 3 days. Seeds of barnyardgrass (E. crus-galli L. Beauv.) were col- lected in the rice field and the large seeds were selected and dried under full sunlight. Then, these seeds were incubated at 50°C for 24 h to break their dormancy and were used for the experiments. Their germination rates were ~76–85%. Laboratory bioassay Dried cucumber plants were soaked in distilled water in the ratio of 4.0 g of dry cucumber to 1 L of distilled water for 0, 3, 5, 7, 9, 11, 13, 15, and 17 days. The dried cucumber plants were also soaked in distilled water in the ratio of 0, 2.67, 4.00, and 5.33 g of dry cucumber to 1 L of distilled water for 9 days. After soaking, the sus- pension (10 mL) of these water extracts was added onto filter paper (No. 1; Whatman International, Maidstone, UK) in a 10 cm Petri dish and 100 seeds of barnyardgrass were sown on the filter paper.After 15 days of incubation at room temperature (~28°C), the germination percent- age, plant height, root length, and fresh weight of barnyardgrass were determined. The experiments were repeated four times in a completely randomized block *Correspondence to: Hisashi Kato-Noguchi, Department of Applied Biological Science, Faculty of Agriculture, Kagawa University, Miki, Kagawa 761-0795, Japan. Email: hisashi@ag.kagawa-u.ac.jp Received 7 February 2007; accepted 16 November 2007 Weed Biology and Management 8, 129–132 (2008) © 2008 The Authors Journal compilation © 2008 Weed Science Society of Japan doi:10.1111/j.1445-6664.2008.00285.x