Screening of allelochemicals on barnyardgrass (Echinochloa crus-galli) and identiﬁcation of potentially allelopathic compounds from rice (Oryza sativa) variety hull extracts
I.M. Chung, K.H. Kim, J.K. Ahn*, S.C. Chun, C.S. Kim, J.T. Kim, S.H. Kim
Department of Crop Science, College of Life and Environment, Konkuk University, HwayangDong KwangJinKu, Seoul143-701, South Korea Received 28 January 2002; received in revised form 18 March 2002; accepted 21 March 2002
Abstract Experiments were conducted to screen 23 known allelochemicals, including sinapic acid, and an equimolar mixture of the chemicals for potential allelopathy on barnyardgrass (Echinochloa crus-galli var. oryzicola), and to identify allelochemical(s) from hull extracts from three rice(Oryza sativa L.) cultivars. In a bioassay, the inhibitory effect was increased as the concentration of allelochemicals increased from 10À5 to 10À3 M. Ferulic, p-hydroxybenzoic, p-coumaric, and m-coumaric acids were the most active compounds and caused the greatest effect on seed germination, germination rate, and total seedling dry weight reduction. phydroxybenzoic acid (10À3 M; pH 4.1) showedthe greatest inhibitory effect on the same parameters. HPLC analysis using three rice cultivars, Janganbyeo, Baekambyeo, and Labelle, showed that the concentration and composition of potentially allelopathic compounds depended upon the cultivar. Hull extracts from the allelopathic cultivar Janganbyeo contained higher levels of phydroxybenzoic acid than did those of the non-allelopathic cultivarsLabelle and Baekambyeo. Nine compounds, including phydroxybenzoic acid (4.29 mg/g) in Janganbyeo, seven compounds including m-coumaric (0.43 mg/g) in Labelle, and ﬁve compounds including p-hydroxybenzoic acid (0.36 mg/g) in Baekambyeo, were detected. Preliminary identiﬁcation by HPLC analysis resulted in peaks with retention times near those of standards, including p-hydroxybenzoic acid that wasconﬁrmed with EI/ MS. It is suggested that these compounds may be, at least, a key factor in rice allelopathy on barnyardgrass, and the information presented may contribute to the development of naturally occurring herbicides. r 2002 Elsevier Science Ltd. All rights reserved.
Keywords: Allelochemicals; Bioassay; Barnyardgrass; Rice; Hull; Allelopathic compound; HPLC; EI/MS
1. Introduction Rice(Oryza sativa L.), one of the principal food crops in Korea, is an annual summer crop. Production is characterized by the heavy use of fertilizers, herbicides, and pesticides, and these practices may lead to environmental problems in both the water and soil of the paddy ﬁeld (Chung et al., 1997). Thus, low-input sustainable agriculture may be an alternative way to minimize environmental costs. Weedproblems such as barnyardgrass (Echinochloa crus-galli), one of the greatest yield limiting weeds in rice cultivation systems, will increase because rice and barnyardgrass often emerge together in the ﬁeld (Ahn and Chung, 2000). Thus, the best way to control barnyardgrass in an environmentally acceptable and sustainable approach is to develop natural com*Corresponding author. Tel.: +822-450-3206;fax: +822-458-8133. E-mail address: email@example.com (J.K. Ahn).
pounds like allelochemicals. However, this assumption may be particularly relevant if synthetic herbicides are difﬁcult to biodegrade in the nature. Many positive studies of allelopathy as a means of ecological weed control by selecting rice cultivars with higher allelopathic potential have been conducted (Fujii, 1992; Garrity etal., 1992; Dilday et al., 1994; Olofsdotter et al., 1995; Chung et al., 1997, 2000, 2001a, b; Chou, 1999; Ahn and Chung, 2000). These studies suggest that allelochemicals released by rice straw (leaf plus stem), decomposed straw, and hulls may control the growth of barnyardgrass and inhibit barnyardgrass seedling establishment. Secondary plant metabolites such as terpenoids, steroids, phenols,...