International Journal of Science and Applied Technology IJSAT, Vol. 2, No. 2, 2017 http://ijsat.unri.ac.id 1 Allelopathic Assessment of Selected Weed Species from BRIS Soil in Terengganu, Malaysia Nornasuha Yusoff 1* , Illa Syafiqah Johari 1 , Nabil Fikri Mohd Shahidi 1 , Nashriyah Mat 1 , Ismail B.S 2 , Yoshiharu Fujii 3 1 School of Agriculture Science and Biotechnology, Faculty of Bioresource and Food Industry, Universiti Sultan Zainal Abidin, Kampus Besut, 22200 Besut, Terengganu, Malaysia. 2 School of Environmental and Natural Resource Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia 3 Department of International Environmental and Agricultural Science, Tokyo University of Agriculture and Technology, Japan. nornasuhayusoff@unisza.edu.my *Corresponding author Abstract: Allelopathy is an economical and environmentally safe method in controlling weeds for sustainable agriculture. Therefore, a laboratory study was conducted to evaluate the allelopathic activity of selected 15 weed species from BRIS soil in Terengganu. For this purpose, the allelopathic assessment was conducted using the sandwich method (through the leaf litter leachate) and also by using the dish-pack method (through the leaf volatilization). The sandwich method was carried out using 5 mg, 10 mg and 50 mg of the donor plant leaf. Meanwhile, the dish-pack method was carried out by using four different distances (41, 58, 82 and 92 mm) away from the donor plant. From the findings, Passiflora foetida showed the highest growth inhibition on lettuce radicle elongation (75.53%) in sandwich bioassay compared to the control, followed by Melilotus officinalis (73.99%) and Chromolaena odorata (63.81%), with all species being broadleaved weeds. In the dish pack bioassay, Passiflora foetida showed the highest growth inhibition on lettuce radicle elongation (46.52%) followed by Croton hirtus (40.82%). It can be concluded that the leaf litter leachate and leaf volatilization of Passiflora foetida showed the highest allelopathic activity compared to other species. Further research need to be conducted on the identification and characterization of allelochemicals using this data as background information for the development of bioactive compounds from weed species into botanical herbicides. Keywords: Allelopathic assessment, weed species, sandwich method, dish-pack method. 1. Introduction The term of allelopathy was introduced by Hans Molisch in 1937, and it is referred as the chemical interaction that takes place among plants, including microorganisms [28]. Allelopathy is a natural process which occurs when a plant interact with other plants. Allelopathy can be defined as the inhibitory or stimulatory effect of one plant including microorganism on another plant through the release of chemical compounds into the environment [19]. The chemical compounds which are secondary metabolite known as allelochemicals are released into the environment from plant parts through leaching, root exudation, volatilization, residue decomposition and other processes in both natural and agricultural systems [1]. Previous studies confirmed that allelochemicals are present in different plant parts including leaves, stems, flowers, stems and buds [26]. Allelochemicals can give effects to the growth and development of plants involving the process of germination, and earlier stage of seedling growth of the targeted plants [27]. The allelochemicals have great potential to be used as herbicides because they are free from the harmful effects compared to the synthetic herbicide in use [12]. Allelopathy has been proposed as the likely mechanism of interference in many weeds which are considered troublesome in cropping systems [11]. In order to evaluate the allelopathic potential of these plant species, many laboratory studies have been conducted either directly through aqueous, organic leachate, extracts of donor plants; or indirectly through extraction of the leachate after addition to the sand agar or medium supporting growth of the donor plants [7, 16]. The sandwich method was developed to test the allelopathic activity that is emitted from leaf litter leachates under control conditions in the laboratory. It is a less time-consuming bioassay method that can be used to screen a large number of samples [15]. The sandwich method was developed by Yoshiharu Fujii in 1994 by using multi-dish plates that consist of six wells with size of