Allelopathy of barnyardgrass (Echinochloa crus-galli) weed: An allelopathic interaction with rice (Oryza sativa)

Abstract

   Barnyardgrass (Echinochloa crus-galli) is one of the most pernicious and problematic weeds in worldwide agriculture. The objective of this review is to highlight the morphology and habitats of this weed, and to present comprehensive information of the allelochemical constituents and pharmacological effects as well as its allelopathic interaction with rice (Oryza sativa L.) based on 115 worldwide literary resources reported over the last 40 years. In laboratory bioassays and root exudates experiments, barnyardgrass showed remarkable inhibition on the growth of the indicator plants. In greenhouse and field experiments, depending on the proportion density of barnyardgrass interference, rice yield is significantly reduced. Major isolated chemical constituents [including 59 compounds, belonging to phenolics, terpenes, steroids, lactones, long-fatty acids, and their derivatives] were identified and isolated from the different parts of this weed including root exudates and infested-soil, which are involved in allelopathic action. Among these, p-hydroxymandelic acids, diethyl phthalate, and two lactones [7,8-dihydro-5,6-dehydrokavain (DDK) and 7,8-dihydrokavain (DHK)], along with a gene cluster for the biosynthesis of 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), may be responsible for the inhibitory effects of barnyardgrass in paddy fields. In attempts to elucidate the modes of action of these allelochemicals and allelopathic interactions between rice and barnyardgrass, it has been shown that the allelopathic actions of barnyardgrass and rice have similar responses in that they sense allelochemicals in the exudation of roots for enhancing allelopathic activity. However, the questions of which compounds play a main role in barnyardgrass allelopathy, and the actual modes of allelopathic interactions with rice remain unclear. This review may provide new insights into barnyardgrass‘ adaptation and invasiveness as well as how the attributable interactions of all its present allelochemicals inhibit the growth of rice and the adjacent plants by allelochemical pathways.