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Compounds from the subterranean part of Johnsongrass and their allelopathic potential
Liu, Yan,Zhang, Chaoxian,Wei, Shouhui,Cui, Hailan,Huang, Hongjuan The Korean Society of Weed Science and The Turfgra 2011 Weed Biology and Management Vol.11 No.3
The allelopathic effects of the exotic invasive weed, Johnsongrass, on Lactuca sativa, a native plant in China, were evaluated and the phytotoxins were investigated under laboratory conditions. The crude extracts (chloroform and ethyl acetate fractions) that were obtained from the ethanol extract of the subterranean parts of Johnsongrass inhibited the germination speed and growth of the roots and shoots of the test plant. The four compounds, ethyl p-hydroxybenzoate, diosmetin, apigenin, and luteolin, were isolated from the extract of the subterranean parts of Johnsongrass first, along with three other compounds (reported previously), p-hydroxybenzaldehyde, p-hydroxybenzoic acid, and dhurrin, and they all were evaluated on L. sativa. At the concentration of <0.5 mmol $L^{-1}$, ethyl p-hydroxybenzoate, dhurrin, and the mixture of the compounds delayed the germination speed of the seeds of L. sativa at 24 h of incubation, while apigenin delayed the germination speed of the seeds of L. sativa at 72 h of incubation. Ethyl p-hydroxybenzoate demonstrated the strongest delaying effect among the phenols and a similar effect was found with apigenin among the flavonoids, wheras ethyl p-hydroxybenzoate induced a drastic inhibition of the germination at 2 mmol $L^{-1}$. In contrast, p-hydroxybenzaldehyde and luteolin had no effect on the germination at any concentration at any stage. All the substances inhibited the shoot and root growth of L. sativa at 3 mmol $L^{-1}$. Increasing the concentration increased the inhibition of the growth of L. sativa.The inhibitory activity of ethyl p-hydroxybenzoate and p-hydroxybenzaldehyde was greater than that of the other compounds. This result suggested that the isolated phytotoxins might contribute to the successful invasion by Johnsongrass.
Predicting the Weed Control Efficacy of Photosynthesis Inhibitors by PPM Method
HONGJUN ZHANG,HAILAN CUI,JIMING YE,XUE LIU,XIANGJUN LI,CORNE KEMPENAAR,SHOUHUI WEI,HANWEN NI 韓國雜草學會 2009 Weed&Turfgrass Science Vol.29 No.3
The experiment was conducted in a greenhouse in Beijing, China, to determine whether weed control efficacy could be predicted based on Plant Photosynthesis Meter (PPM) values measured shortly after the application of photosynthesis inhibitors. The decrease of PPM values of the weed leaves treated with the mixture of atrazine and bentazone could be measured 1 day after treatment (DAT). The decreased extents depended on weed susceptibility and application dosage. There was significant correlation between the PPM values of the treated leaves 1 to 3 DAT and the biomass reduction 14 DAT. The experimental findings indicated that PPM values measured in early days after treatment could give reasonable prediction on weed control. The herbicide usually provided 90% control by weed biomass when PPM value was about 20 and relatively poor control when PPM value over 20.