Potent herbicidal activity of Murraya euchrestifolia piperitone monoterpenes against Echinochloa crus-galli in vitro

Murraya euchrestifolia Hayata extract showed strong herbicidal effect on Echinochloa crus-galli (L.) P. Beauv. Four active piperitone monoterpenes ( 1 - 4 ), containing two undescribed ones ( 1 and 2 ), were separated from methanol extract of leaves and branches of M. euchristifolia for the first time using bioassay-guided method. This investigation is the first to evaluate the herbicidal effect of 1 - 4 and preliminarily analyze their structure-activity relationship. Mureupiperitone A ( 1 ) and (-)-(4 R ,6 S )-6-hydroxy-piperitone ( 4 ) exhibited outstanding inhibitory effect on the growth of E. crus-galli . at 300 μ g/mL, with inhibition rates of 62.81 % and 64.47 % on the seed germination, 64.92 % and 65.73 % on the shoot growth, and 82.08 % and 83.02 % on root growth, respectively. The IC 50 values of 1 against the root and shoot development of E. crus-galli were 87.97 and 175.84 μ g mL −1 , respectively, which were higher than / close to those of the positive herbicide (Nic). The results of morphological, physiological, and biochemical experiments suggested that the suppression of 1 on seed germination of E. crus-galli is attributed to the insufficient energy supply caused by the decrease in α -amylase activity, while the inhibition of 1 on the development of seedling roots is mainly caused by the accumulation of ROS. Thus, 1 and 4 may have the potential to be used as a template for the advancement of new herbicides or as a probe for the discovery of new herbicidal targets. • The extracts of Murraya euchrestifolia Hayata showed strong herbicidal activity. • Four herbicidal piperitone monoterpenes were isolated, including two new ones. • 1 and 4 have comparable phytotoxicity to nicosulfuron against Echinochloa crus-galli (L.) P. Beauv. • 1 can inhibit α -amylase activity of seeds and induce ROS amassment of root tip.