www.tropicalplantresearch.com 1 Received: 11 October 2016 Published online: 31 January 2017 https://doi.org/10.22271/tpr.2017.v4.i1.001 ISSN (E): 2349 – 1183 ISSN (P): 2349 – 9265 4(1): 01–06, 2017 DOI: 10.22271/tpr.2017.v4.i1.001 Research article Seed germination inhibitory effect of Caryota urens L. seed pericarp on rice and associated weeds S. I. Fonseka 1 , S. Adikari 1 , L. R. Jayasekera 1 *, P. Ranasinghe 2 and G. A. S. Premakumara 2 1 Department of Botany, University of Kelaniya, Sri Lanka 2 Industrial Technology Institute, Colombo, Sri Lanka *Corresponding Author: ranjith@kln.ac.lk [Accepted: 05 January 2017] Abstract: Previous studies have shown that the Caryota urens seed pericarp possesses botanicals capable of inhibiting seed germination. Extracts made from C. urens pericarp were tested at different concentrations to find out its inhibitory activity. Three rice varieties (Bg 305, Bg 358, Bg 368) and the rice weeds (Echinochloa crus-galli, Ischaemum rugosum and Ipomoea aquatica) were tested. Percentage germination was measured for 7 days at 2 day intervals. The methanol extract of dried seed pericarp significantly reduced the seed germination, indicating that the concentration of the inhibitory substance/s in C. urens pericarp is higher in methanol extracts than the water extracts. Dried seed pericarp showed the highest inhibitory effect on the seed germination. The germination of all rice cultivars and weed species tested were completely inhibited by 100 and 200 mg.ml -1 concentrations, suggesting that the C. urens seed pericarp has a seed germination inhibitory effect on all weeds tested. In general, the germination inhibitory effects were maximal at high concentrations than at lower concentrations. Potential for using C. urens pericarp for weed control is highlighted. Keywords: Caryota urens - Seed pericarp - Germination - Rice - Weeds. [Cite as: Fonseka SI, Adikari S, Jayasekera LR, Ranasinghe P & Premakumara GAS (2017) Seed germination inhibitory effect of Caryota urens L. seed pericarp on rice and associated weeds. Tropical Plant Research 4(1): 1–6] INTRODUCTION The ever increasing demand for food with the exponential increase in human population demands maximal achievements in crop production. Development of effective and environmental friendly weed control measures is one area of importance in this respect. Weeds and weed control have become a major cost factor determining the economic profitability of crop production worldwide. Weeds, being the major biotic stress for most crops including rice, compete with crops for light, nutrients and moisture, resulting in significant decrease of yield and quality of crop harvest. In the light of the above, studies on locally available natural sources that have a potential to control weeds become relevant to develop appropriate, environmental friendly control measures that suit the agricultural background and economy of Sri Lanka. Allelopathy is defined as a mechanism by which plant, directly or indirectly affects, inhibits or stimulates growth of other plants by the production of chemical compounds or allelochemicals released to the environment (Ridenour & Callaway 2001). The use of allelochemicals by allelopathic plants/plant parts for weed management has received attention in recent times (Weston 1996) in view of their environmental friendly nature as opposed to synthetic chemicals. Hence the use of natural substances from plants is considered as a low input and sustainable approach to integrated weed management, a practice that helps reduce the increasing incidences of herbicide resistance in weeds as well (Mayer & Mayber 1989, Materechera & Hae 2008). Studies have shown the inhibitory effects of certain plants not only on weeds but also on growth and yields of crop species. The allelopathic and herbicidal effectiveness of different plant species have shown to depend on the plant part (Oudhia 2003). Therefore investigations are required to explore plants and respective plant parts with effective allelopathic activity, especially in the control of agricultural weeds (Materechera & Hae 2008). The inhibitory effects of extracts obtained from different seed pericarps and plant parts on seed germination of