Study On Allelopathic Potential And Potential Allelochemicals Of Parthenium Hysterophorus L.

Parthenium hysterophorus L., originally found in USA and Mexico, is a noxious invasive alien weed, and it has become widerspread in many countries and regions. In these invaded countries and regions, this weed has caused serious loss and threatened native biodiversity, ecosystem integrity and even the health of human and livestock. Parthenium hysterophorus L. was first found in the 1950s and has now been widely disseminated to Yunnan, Guangxi, Guangdong and other places in China. In order to use Parthenium hysterophorus L. resource, this article preliminarily studied the allelopathy of Parthenium hysterophorus L.. The results were as follow:1. Digitaria sanguinalis, Echinochloa crusgalli, Abutilon theophrasti and Cucumis sativus L. were measured for evaluating the allelopathic potentional of aqueous extracts from Parthenium hysterophorus L. by the way of indoor Petri dish bioassay and defining allelopathic potentional of different organs of Parthenium hysterophorus L. . Results showed that the allelopathic potentional of aqueous extracts of root, stem, leaf and flower were different. The aqueous extracts from leaf and flower had the highest inhibitory effects which became stronger with increasing of concentration, Echinochloa crusgalli and Cucumis sativus L. were wholly inhibited at the concentration of 0.2 g FW/mL, and the inhibition rates of indexes of Digitaria sanguinalis and Abutilon theophrasti were more than 88% at the same concentration. Both promotion and inhibition were expressed by aqueous extracts of root and stem, which showed the concentration effects that test receptor plans were promoted at lowest concentration while inhibited at highest concentration. The results indicated that leaf and flower had the highest allelopathic inhibitory effects, following was stem and root. It indicated that different organs Parthenium hysterophorus L. had different kinds and contents of allelochemicals.2. Under the natural condition, Parthenium hysterophorus L. could release allelochemicals to environment by the ways of root exudate, eluviation of the parts aboveground and volatilization of flower and leaf. The results showed that Parthenium hysterophorus L root exudates and eluviation of the parts aboveground inhibited the germination and growth of treated plant. The seedling growth of E. crusgalli and D. sanguinalis enclosed in obturator with fresh P. hysterophorus flower was inhibited. The seedling growth of D. sanguinalis enclosed in obturator with fresh P. hysterophorus leaf was also inhibited, while E. crusgalli was slightly accelerated.3. Indoor Petri dish bioassay was adopted to study allelopathic autotoxicity effects of Parthenium hysterophorus L.. The results showed that the flower, stem and leaf aqueous extracts inhibited the germination and growth of Parthenium hysterophorus L., and the inhibitory effect of leaf and flower were stronger than that of stem. The results of leaf aqueous extract and its ethyl acetate fraction, n-butanol fraction and residuary water fraction on Parthenium hysterophorus L. indicated that thyl acetate fraction had the highest bioactivity exhibited the most inhibitory effect on Parthenium hysterophorus L., and it increased became stronger as the concentration increased, The results indicate that Parthenium hysterophorus L.has allelopathic autotoxicity effect.4. In order to ascertain the allelopathy of Parthenium hysterophorus L., the greenhouse pot experiment were performed to investigate the effects of aqueous extract on physiological and biochemical mechanism in wheat. The results showed aqueous extract of flower reduced the net photosynthetic rate and content of chlorophyll of wheat, and this inhibition became stronger as the concentration of the extract increased. The net photosynthetic rate and content of chlorophyll reduced by 44.3 % and 15.0 % at 10 % respectively. CAT activity decreased, and MDA contents increased, and N, NR and GS activities first decreased and then increased, while POD and SOD activities first increased and then decreased with the concentration of extract increased. The net photosynthetic rate, transpiration rate and stomatal conductance were inhibited when wheat was treated with 2%, 6% and 10% leaf aqueous extract, and the intercellular CO2 concentration was decreased at first and increased subsequently while stomatal limitation value and transpiration efficiency were increased at first and decreased subsequently, and aqueous extract also decreased the content of Chl a, Chl b, chlorophyll, carotenoid and the ratios of Chl a/Chl b, the net photosynthetic rate and content of chlorophyll reduced by 82.8% and 49.4 % at 19.1 % at 10 % respectively. CAT activity decreased, and N, MDA contents and NR activity increased, and GS activity first decreased and then increased, while POD and SOD activities first increased and then decreased with the concentration of extract increased,5. The allelopathic effect of Parthenium hysterophorus L. flower and leaf aqueous extract and its ethyl acetate fraction, n-butanol fraction and residuary water fraction on the germination and seedling growth of 6 kinds of plants were studied by the way of indoor Petri dish bioassay. The results showed that ethyl acetate fraction had the highest bioactivity in flower and leaf. Using middle-pressure Liquid chromatography isolated and purified the ethyl acetate fraction of flower aqueous extract. The potential allelochemical were sieved andtraced by bioactivity on receptor. After isolating and purifying, several fractions wereidentified by GC-MS, and ethyl acetate fraction of leaf aqueous extract and volatile were alsoidentified by GC-MS. 16 compounds were identified in ethyl acetate fraction by the methodof GC-MS, and the constituents are mainly hydrocarbon and its derivatives, naphthalenes,alcohols, benzenes, acids, ketones and esters. 3-(3,3-dimethyloxiran-2-yl)-2,2-dimethylpropionic acid ethyl ester has not been reported, and the herbicidal activities ofMethoxyacetic acid, 4-Methyl-3-penten-2-one and 4-Hydroxy- 4-methyl-2-pentanone werenot tested. The main compounds were Aristolene epoxide, Diisooctyl phthalate,Dihydroxanthin, 7-Hydroxy-6,9 a-dimethyl-3-methylene-Decahydro-azuleno[4,5-b]furan-2,9-dione, Decahydro-8,9-dihydroxy -6,9a-dimethyl-3-methylene-Azuleno [4,5-b] furan-2 (3H)–one and Oleic Acid in ethyl acetate fraction of leaf aqueous extract. The volatile from P.hysterophorus flower contained 17 components. The main component was Myrcene (42.67%)Ocimene (26.28%), beta-Pinene (15.74%), Alcohol (6.32%) and Camphene (3.76%). Therewere 18 components in the volatile from P. hysterophorus leaf. The main component wasMyrcene (28.07%), beta-Pinene (14.52%), Camphene (14.01%), alpha-Pinene (12.44%) and 66-Dimethyl-2-methylenebicyclo [3.1.1]heptane (10.08%).6. The main purpose of the experiment was conducted to study the effects of six kinds ofpotential allelochemicals (Myrcene, Ocimene,β-pinene, Methoxyacetic acid, 4-Methyl-3-penten -2-one and 4-Hydroxy-4-methyl-2-pentanone). The results showed that Myrcene,Ocimene andβ-pinene had different effects on germination and seedling growth of treatedplants, and antagonistic effect or additive action was the main synergistic effect to Myrceneand Ocimene (Myrcene andβ-pinene). Methoxyacetic acid, 4-Methyl-3-penten-2-one and4-Hydroxy-4- methyl-2-pentanone had inhibitory effect on Rhizoctonia cerealis, Alternariasolan(iEllis et Martin) Jones et Grout, Botrytis cinerea, Fusarium oxysporum.f sp.fragariae,Colletotrichum gloeosporioides and Rhizoctonia solanikohn,and Methoxyacetic acidand 4-Methyl-3- penten-2-one exhibited more inhibitory effect on pathogens than4-Hydroxy-4-methyl- 2-pentanone. Methoxyacetic acid, 4-Methyl-3-penten-2-one and4-Hydroxy-4-methyl-2- pentanone had inhibitory effect on germination and seedling growthof treated plants. Synergistic action was the main synergistic effect to Methoxyacetic acidand 4-Methyl -3-penten-2-one (4-Methyl -3-penten-2-one and 4-Hydroxy-4-methyl-2-pentanone).