Screening For Natural Herbicide To A Noxious Weed Ligularia Virgaurea In Psychro-grasslands

The usage of chemistry herbicide has already not adapted the social need of the sustainable development nowadays,The development of safety and efficient natural herbicide gradually becomes the most effective path to prevent grass.The Ligularia virgaurea is one kind of noxious weeds,distributed widely in psychro-grasslands in the east of Qinghai-Tibet Plateau of China.Not only it breaks the structure of the grassland ecosystem,but also endangers the development of animal husbandry extremely.In this thesis,made use of allelopathy between plants,we screened the donor plants which can inhibit Ligularia virgaurea germination stage,and compared the allelopathic potential of donors.In addition,we isolated and identified activated compounds from Ipomoea cairica,a screened donor,and studied the allelopathy of allelochemicals.The purpose is to provide not only empirical foundation for the development of plant herbicide to Ligularia virgaurea,but also a theoretioal basis for the research of a new kind of natural herbicide.The main results are as follows:1.With water extracts from 31 common plants belonging to 13 families which distributed the same or different region with Ligularia virgaurea,we screened 9 plants that have allelopathic activity to germination stage of Ligularia virgaurea.It was shown that there were different mode and strength of allelopathy with different species.Even the same donor plant,under the same environment,could show species specificity to different receptors on allelopathic influence.2.The results indicated that seven kinds of plant aqueous extracts can inhibit seed germination of Ligularia virgaurea but less injurious effect to Elymus nutans,a common pasture plant.Their were 0.0500g/ml Wedelia trilobata(m=-0.5443), 0.0500g/mL Bidens pilosa(m=-0.5929),0.1000g/mL(m=-0.6100)and 0.0250 g/mL(m=-0.5866)Adenostemma lavenia,0.0500g/mL Stellera chamaejasme(m =-0.5803)and 0.0250g/mL(m=-0.5697),0.0500g/mL(m=-0.5572)Ipomoea cairica.The results suggest that their can be used as the natural herbicide to exploit at seed germination stage of Ligularia virgaurea.3.Allelopathic activity of Ipomoea cairica is stronger than the other don-ors,we isolated and identified two allelochemicals belonging to flavonoid in it:3-3'-5-Trihydroxy-4'-7-dimethoxyflavone and 3-3'-5-Trihydroxy-4'-7-dime-thox yflavone-3-O-sulfate.The result indicated that there is selectivity for two comp-ounds.Either germination rate or germination index,the two compounds show-ed allelopathic inhibition significantly to Cucumis sativus seed when they tested receptors independently,but much weaker to Brassica pekinensis seed.4.There were antagonistic effects between two allelochemicals in Ipomoea cairica.The mixed solution of them tested Ligularia virgaurea,Raphanus sativus, Cucumis sativus and Brassica pekinensis seed respectively,Either germination rate or germination index,indicated that allelopathic inhibit strength was weaker than two allelochemicals tested them independently.