Scientia Horticulturae 134 (2012) 26–31 Contents lists available at SciVerse ScienceDirect Scientia Horticulturae journa l h o me page: www.elsevier.com/locate/scihorti Autotoxicity in beans and their allelochemicals Md. Asaduzzaman a,b , Toshiki Asao a,∗ a Department of Agriculture, Faculty of Life and Environmental Science, Shimane University, 2059 Kamihonjo, Matsue, Shimane 690-1102, Japan b United Graduate School of Agricultural Sciences, Tottori University, Koyama-cho, Minami Tottori, Tottori 680-8553, Japan a r t i c l e i n f o Article history: Received 14 January 2011 Received in revised form 18 November 2011 Accepted 29 November 2011 Keywords: Autotoxicity Pisum sativum Phaseolus vulgaris Vicia faba Root exudates Allelochemicals Activated charcoal Bioassay a b s t r a c t The autotoxicity of Pisum sativum, Phaseolus vulgaris, and Vicia faba were investigated in hydroponics either with or without activated charcoal (AC) addition. Growth and yield of the three beans were sig- nificantly reduced when grown in the culture solution without AC addition. In P. sativum plants grown in non-renewed culture solution without AC, the number of pods, pod fresh mass, number of seeds, and seed fresh mass were reduced by about half compared with those with AC. The number of pods plant -1 and fresh mass of pods -1 plant in P. vulgaris, as well as pod number in V. faba, were decreased significantly to 49–67% without AC addition. The identified allelochemicals were benzoic, salicylic, and malonic acids in the root exudates of P. vulgaris and lactic, benzoic, p-hydroxybenzoic, vanillic, adipic, succinic, malic, glycolic, and p-hydroxyphenylacetic acids in V. faba. Bioassay of the identified allelochemicals revealed that benzoic, salicylic, and malonic acids significantly reduced the growth of P. vulgaris even at low con- centrations. In V. faba, benzoic acid at 50 M significantly reduced root length, and shoots fresh and dry mass by over 81% of those of the control, whereas adipic and p-hydroxyphenylacetic acids decreased root length to 87 and 88% of that of the control, respectively. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Beans are grain legumes that belong to the family Leguminosae, which includes food and forage legumes. Bean plants are cultivated primarily for their seeds, which are harvested at maturity and are rich in protein and energy. They are used either for animal feed or for human consumption. The major grain legumes are Pisum sativum, Vicia faba, Lens culinaris, Glycine max, Phaseolus vulgaris, Lupinus spp., and Cicer arietinum. These grain legumes are generally intercropped with cereals to enhance crop yield, increase nitro- gen use efficiency, and reduce weed infestation and the occurrence of plant disease (Willey, 1979; Jensen, 1996; Hauggaard-Nielsen et al., 2001, 2008). Among the grain legumes, some edible beans are used as vegetables and intensively cultivated in the same farmland year after year. The production of these common bean plants and other perennial legumes declines in replanting conditions owing to autotoxicity, a form of intraspecific allelopathy that occurs when a plant species releases chemical substances that inhibit or delay germination and growth of the same plant species (Putnam, 1985; Abbreviations: AC, activated charcoal; EC, electrical conductivity; h, hour; GC–MS, gas chromatography–mass spectrometry; M, molar; DE, diethyl ether; EA, ethyl acetate; EI, electron impact; FM, fresh mass; DM, dry mass; HPLC, high perfor- mance liquid chromatography; rpm, revolutions per minute; M, micro molar. ∗ Corresponding author. Tel.: +81 852 34 1817; fax: +81 852 34 1823. E-mail addresses: asadcbt@yahoo.com (Md. Asaduzzaman), asao@life.shimane- u.ac.jp (T. Asao). Miller, 1996; Singh et al., 1999). Allelopathy has been investigated in some beans such as in P. sativum (Kato-Noguchi, 2003), Mucun pruriens (Fujii et al., 1991), Glycine max (Huber and Abney, 1986; Xiao et al., 2006; Yan and Yang, 2008), and Cicer arietinum (Yasmin et al., 1999). l-DOPA and cynamidine has been found to be poten- tial allelochemicals identified in Mucuna pruriens and Vicia villosa, respectively (Fujii, 2003). It has been found that, in addition to com- mon beans, several other species within the Leguminosae family contain secondary plant products that have allelopathic potential (Rice, 1984). In field experiments, it has been reported that residues and extracts of pea plants suppressed the growth and population size of several plant species (Purvis, 1990; Schenk and Werner, 1991; Tsuchiya and Ohno, 1992; Akemo et al., 2000). Phytotoxic substances in P. sativum root exudates have been reported by sev- eral researchers (Hatsuda et al., 1963; Yu and Matsui, 1999) and, recently, pisatin has been identified as an inhibitory chemical from its shoots (Kato-Noguchi, 2003). Aqueous leachates of dry shoot of P. vulgaris that contain phenolics showed allelopathic effects on several crop species (Nava-Rodríguez et al., 2005). Autotoxic- ity due to root exudates found to be involved in growth reduction in Glycine max monocropping, which decreased plant biomass and root triphenyl tetrazolium chloride-reducing activity as well as seedlings after exposure to root exudates, exhibited higher activi- ties of superoxide dismutase and guaiacol peroxidase (Xiao et al., 2006). Successive culture of the same crop on the same land for years cause soil sickness or replanting injuries (Hirano, 1940; Bonner and 0304-4238/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2011.11.035