Analysis Of The Allelopathic Effects Of Yellow-top Weed (Flaveria Bidentis) On Wheat Plant

Yellow-top(Flaveria bidentis)weed,originated from South America,is a new invasive plant species in northern China.Since F.bidentis was first recorded in China in 2001,it is now widely distributed in areas of more than 47 counties in Hebei Province and Tianjin City.The distribution regions in China are still quickly expanding.Our field surveys suggested that this weed can easily establish virtual monocultures,develop large population communities once established. The present research was conducted mainly to analyze the potential allelopathic effects of yellow-top weed on wheat,and to study the allelochemical from the leachates of yellow-top plants.1.Beaker-blotting paper bioassay was done to analyze the aUelopathic effect of yellow-top. Results from the experiment showed that water extract from the aerial part of yellow-top plants, water extract from the roots and ethanol extract of rhizospheric soil were shown to inhibit wheat seedling growth significantly and the inhibition was highered as the concentration increased.The inhibition effect of water extract from the fresh aerial part on wheat seedlings was stronger than the water extract from the roots at the same concentration.The highest inhibition rates of wheat roots length,seedling length,root weight arid seedling weight were 21.0%,23.6%,28.3%and 20.2%, respectively after treatment with the water extracts of fresh aerial parts of yellow-top plants at the concentration of 10%.The water extract of yellow-top roots at concentration of 10%inhibited wheat root length,root weight,seedling length and seedling weight by 16.9%,13.3%,8.8%and 13.5%, respectively.The inhibition rates of the length of roots and seedlings,the fresh weight of roots and seedling which were treated under the ethanol extract of rhizospheric soil could reach 15.6%,23.6%, 27.9%and 35.8%,respectively at the concentration of 5.0 g/mL.The inhibition rates under the treatment of water extracts of dry aerial parts were 40.6%on the length of roots and 25.5%on the seedlings,32.2%on the fresh weight of roots and 29.4%on the seedling at the concentration of 0.01gDW/mL2.After treated with water extract of dry yellow-top aerial part,morphology of hairy rootsof wheat root system were affected inversely and significantly.After wheat seedlings were treated for 7 days,the hairy roots became very sparse and varied in length at the concentration of 0.01 gDW/mL; the length and density of hairy roots declined as the extract concentration increased and there were hardly any hairy roots visible on the main roots of wheat after the treatment at concentration of 0.04gDW/mL.3.The contents of MDA,WSS,Pro,Chla,Chlb,and Chl in wheat root tissues were measured 7 days after wheat seedlings were treated with 4 concentrations(0.01,0.02,0.03å’Œ0.04 gDW/mL) of water extract from the dry yellow-top aerial part.Experimental results showed that the contents of melondialdehyde(MDA)and water soluable sugar(WSS)in wheat roots increased significantly at all concentrations of dry yellow-top extract.The content of free proline was highered at 0.03 gDW/mLand 0.04 gDW/mL,but no signjficantly change was detected at lower concentrations of dried yellow-top extract.The contents of chlorophyll a,b and total chlorophyll were not markedly altered at 0.01gDW/mL and 0.02 gDW/mL and they decreased significantly at the higher concentrations of yellow-top extract tested.4.The allelochemical complex was isolated from yellow-top roots tissues stepwisely with the four commonly used organic solents(petroleum ether,chloroform,ethyl acetate and N-butanol). Bioassay showed that the extract by N-butanol was the most active component and it suppressed growth of wheat root and aerial parts by about 23%and 19%,respectively,when appliedat a concentration of 0.1 mg/mL.This extract was separated with silica gel column chromatography.The F4 portion on the silica gel column was shown most active by bioassay;the root length and weight, seedling height and weight were reduced by 31.5%,34.8%,43.3%and 46.4%,respectively.A potential allelochemical was obtained from the F4 portion by high-speed countercurrent chromatography(HSCCC).This chemical compound was a kind of flavonoid determined integratedly by the Wilstatter cyanidin,metal-salt(FeCl₃)complexation,bode acid toleration and alkaline(NaOH)reagent coloration reactions.It suppressed wheat growth significantly and the IC₅₀ (concentration for 50%inhibition)was measured as 0.352 mg/mL for root length and 0.271 mg/mL for seedling suppression.