| Chemical pesticides have helped greatly in increasing crop yields and warding off pests and diseases,but they have also brought about environmental pollution and other drawbacks,and are in urgent need of improvement and transformation.Coumarins are widely found in nature and have strong potential for weed control,and are expected to be developed into new bio-sourced pesticides with high environmental efficiency.Currently,coumarins and their derivatives are mainly used in agriculture for regulating plant growth,helping plants to resist pests and diseases,as well as for rodent control,etc.They have been widely used for insect control,fungicide and rodent control,but there is still great potential for their application as herbicidal active substances to inhibit weed growth.Therefore,in order to investigate the inhibitory effects of coumarins on different plants at different times of the year,six coumarins and their derivatives with different structures and high biological activity,6-methyl coumarin,7-hydroxy coumarin,4-hydroxy coumarin,esculin,coumarin 120 and simple coumarin,which are widely found in nature,were selected and tested by bioassay in Petri dishes and in pots in the laboratory.Seed germination tests and potted seedling tests were carried out to compare the potential and differences in the application of coumarins as pre-emergence and post-emergence herbicides.Seed germination trials were conducted using the six coumarins mentioned above on ryegrass(Lolium perenne),setaria(Setaria viridis),white clover(Trifolium repens L.),Portulaca oleracea,horsetail(Dichondra micrantha)and bluegrass(Poa annua L.)seeds were treated and pot trials were conducted to compare and explore the potential of post-emergence herbicides using treatments on six coumarin-like substances white clover versus ryegrass seedlings.The main findings of the study were as follows:1.Compared to control,when used as pre-emergence herbicides,7-hydroxycoumarin,6-methylcoumarin,4-hydroxycoumarin and simple coumarin had a strong inhibitory effect on the germination of ryegrass,setaria,white clover seeds(P<0.05),6-methylcoumarin and simple coumarin could completely inhibit the germination of bluegrass The root length of setaria and Portulaca oleracea was significantly reduced by 7-hydroxycoumarin and 4hydroxycoumarin treatments(P<0.05),and the fresh and dry weights of setaria and Portulaca oleracea were significantly reduced by 6-methylcoumarin and simple coumarin treatments(P<0.05).Overall,simple coumarin and 6-methyl coumarin had the strongest combined herbicidal activity,with the strongest inhibition of white clover and setaria;7hydroxycoumarin and 4-hydroxycoumarin had the next strongest inhibition of ryegrass and Portulaca oleracea;The herbicidal activity of coumarin 120 and esculin was weaker.2.Compared with control,the root height of white clover and root length of ryegrass were significantly lower(P<0.05)and the fresh weight of white clover roots was significantly lower(P<0.05)when post-emergence treatment was applied.0.05);6methylcoumarin,simple coumarin and coumarin 120 significantly reduced the aboveground fresh weight of white clover and ryegrass(P<0.05);the above-and below-ground biomass of ryegrass was significantly reduced(P<0.05)and the SPAD value was significantly reduced(P<0.05);the above-and below-ground biomass of white clover and ryegrass was significantly reduced(P<0.05);the above-and below-ground biomass of white clover and ryegrass was significantly reduced(P<0.05).clover and ryegrass showed a sharp increase in MDA content and POD activity values(P<0.05),ryegrass CAT activity values also showed a significant increase(P<0.05);4-hydroxycoumarin and simple coumarin triggered a significant increase in white clover SOD activity values(P<0.05),7hydroxycoumarin treatment in SOD activity was enhanced in ryegrass(P<0.05),while 6methylcoumarin,simple coumarin and coumarin 120 significantly reduced SOD activity in ryegrass(P<0.05);soluble sugar content of white clover was increased under esculin,6methylcoumarin and simple coumarin treatment(P<0.05),and 4-Hydroxycoumarin,esculin,coumarin 120,6-methylcoumarin and simple coumarin reduced ryegrass soluble sugar content(P<0.05);white clover soluble protein content was significantly reduced under esculin treatment(P<0.05),and all six coumarins significantly reduced All six coumarins significantly reduced the soluble protein content of ryegrass(P<0.05);esculin,coumarin 120,6-methyl coumarin and simple coumarin reduced the GA3 content of white clover and ryegrass(P<0.05);all six coumarins significantly increased the ABA content of white clover and ryegrass(P<0.05).(P<0.05);all six coumarins increased the ABA content of white clover and ryegrass significantly(P<0.05).Coumarins interfered with seedling growth mainly through their effects on changes in endogenous hormone content,osmoregulatory substances,antioxidant enzyme activity,growth of nutrient organs,photosynthesis and the functional state of cell membranes,mainly affecting ABA content and antioxidant enzyme activity.Compared to the seed germination test as a pre-emergence treatment,white clover was more highly inhibited in the post-emergence treatment,while root length development was less stressed than in the pre-emergence treatment.During seed germination,6-methylcoumarin,simple coumarin and 7-hydroxycoumarin showed stronger inhibition of white clover and ryegrass,while 6-methylcoumarin,simple coumarin and coumarin 120 showed stronger inhibition in the post-emergence treatment,and coumarin with even substituents and non-polar substituents showed stronger inhibition.3.Based on the above results,coumarins have the potential to be developed as preemergence and post-emergence herbicides or herbicide intermediates.Combining the functional structures and synthesis levels of coumarins,6-methyl coumarin,simple coumarin and 7-hydroxy coumarin,4-hydroxy coumarin have the potential to be developed as pre-emergence herbicides,6-methyl coumarin,simple coumarin and coumarin 120 have the potential to be developed as post-emergence herbicides,and 6-methyl coumarin,simple coumarin and coumarin 120 have the potential to be developed as post-emergence herbicides.The potential of 6-methylcoumarin,simple coumarin and coumarin 120 as postemergence herbicides is even greater,while the factors affecting herbicidal efficacy,such as the selectivity pattern between seed species with different chemical structures and the mechanism of efficient herbicidal application,need to be further investigated. |
PDF Full Text Request