title: Phytotoxic substances with allelopathic activity may be central to the strong invasive potential of Brachiaria brizantha.
abstract: The grass Brachiaria brizantha, native to eastern Africa, becomes naturalized and dominant quickly in the non-native areas. It was hypothesized that phytotoxic chemical interaction between this plant and native plants may play an important role in the invasion of B. brizantha. However, no potent phytotoxic substance has been reported in this species. Therefore, we investigated possible allelopathic activity and searched for phytotoxic substances with allelopathic activity in B. brizantha. An aqueous methanol extract of B. brizantha inhibited the growth of roots and shoots of garden cress (Lepidium sativum), lettuce (Lactuca sativa), timothy (Phleum pratense) and ryegrass (Lolium multiflorum) seedlings. The extract was purified by several chromatographic runs and three allelopathically active substances were isolated and identified by spectral analysis as (6R,9R)-3-oxo-α-ionol, (6R,9S)-3-oxo-α-ionol and 4-ketopinoresinol. (6R,9R)-3-Oxo-α-ionol and (6R,9S)-3-oxo-α-ionol inhibited root and shoot growth of garden cress at concentrations greater than 30 and 10 μM, respectively. The activity of (6R,9S)-3-oxo-α-ionol was 5.3- to 6.2-fold that of (6R,9R)-3-oxo-α-ionol. The stereochemistry of the hydroxyl group at position C-9 may be important for the inhibitory activities of those compounds. 4-Ketopinoresinol inhibited root and shoot growth of garden cress at concentrations greater than 30 μM. The growth inhibitory activity of (6R,9S)-3-oxo-α-ionol was the greatest and followed by 4-ketopinoresinol and (6R,9R)-3-oxo-α-ionol. These results suggest that those phytotoxic substances may contribute to the allelopathic effect caused by B. brizantha and may be involved in the invasion of B. brizantha.
authors.affiliation: Department of Applied Biological Science, Faculty of Agriculture, Kagawa University, Miki, Kagawa 761-0795, Japan. Electronic address: hisashi@ag.kagawa-u.ac.jp.
authors.forename: Hisashi
authors.initials: H
authors.lastname: Kato-Noguchi
authors.affiliation: Department of Applied Biological Science, Faculty of Agriculture, Kagawa University, Miki, Kagawa 761-0795, Japan.
authors.forename: Ai
authors.initials: A
authors.lastname: Kobayashi
authors.affiliation: Department of Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku, Yokohama 223-8522, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Ohno
authors.affiliation: Department of Applied Biological Science, Faculty of Agriculture, Kagawa University, Miki, Kagawa 761-0795, Japan.
authors.forename: Fukiko
authors.initials: F
authors.lastname: Kimura
authors.affiliation: International Environmental and Agricultural Sciences, Tokyo University of Agriculture and Technology, 3-5-8, Saiwai-cho, Fuchu, Tokyo 183-8509, Japan.
authors.forename: Yoshiharu
authors.initials: Y
authors.lastname: Fujii
authors.affiliation: Department of Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku, Yokohama 223-8522, Japan.
authors.forename: Kiyotake
authors.initials: K
authors.lastname: Suenaga
mesh_terms: D064089:Allelopathy; D035201:Brachiaria / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D003512:Cyclohexanones / Q000494:pharmacology*; D005663:Furans / Q000494:pharmacology*; D031220:Lepidium sativum / Q000187:drug effects / Q000254:growth & development; D018545:Lactuca / Q000187:drug effects / Q000254:growth & development; D017705:Lignans / Q000494:pharmacology*; D000432:Methanol / Q000737:chemistry; D010936:Plant Extracts / Q000494:pharmacology*; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development; D018520:Plant Shoots / Q000737:chemistry / Q000187:drug effects / Q000254:growth & development; D010944:Plants / Q000187:drug effects*; D006109:Poaceae / Q000187:drug effects / Q000254:growth & development
chemical_list: C525367:3-oxo-alpha-ionol; C572940:4-ketopinoresinol; D003512:Cyclohexanones; D005663:Furans; D017705:Lignans; D010936:Plant Extracts; D000432:Methanol
keywords: Allelopathy; Brachiaria brizantha; Growth inhibitor; Invasive plant; Phytotoxin