Study On Welsh Onion Root Exudates And Their Allelopathy On Cucumber And Fusarium Oxysporum F.Sp. Cucumerinum

Cucumber(Cucumis sativus L.) is one of the main vegetables under protected cultivation, and continuous cropping obstacles have become important factors restricting high production and sustainable development, the control of continuous cropping obstacles has been paid more and more attention. Previous studies have shown that rotation with Welsh onion can significantly ameliorate the physicochemical and biological properties of continuous cropped cucumber soil in greenhouse and improve the diversity of microorganisms, the number of bacteria and actinomycetes were increased and fungi was reduced, the reproduction of Fusarium oxysporum f.sp. cucumerinum was inhibited, and the growth and yield of cucumber were promoted, but the internal mechanism is not clear. Welsh onion root exudates and its allelopathy may be the important reasons. Therefore, this paper has studied on the Welsh onion(Allium fistulosum L.) root exudates and their allelopathy on cucumber and Fusarium oxysporum f.sp. cucumerinum, the main allelochemicals were isolated, identificated and verified, and execpected explaining the reasons through allelopathy of rotation with Welsh onion control the continuous cropping obstacles of cucumber in greenhouse and providing theoretical basis for the development of culture system reasonably. The main results were as follows:1. After Welsh onion rotation, the EC of rhizosphere soil was decreased significantly while the pH increased. The number of bacteria and actinomycetes in Welsh onion rhizosphere soil were increased, the number of fungi and Fusarium oxysporum were decreased, and the activities of invertase, urease, catalase, polyphenol oxidase were increased. Relative content of diethyl phthalate and dibenzofuran were higher in Welsh onion rhizosphere soil than cucumber rhizosphere soil, and containing six sulfur compounds, five compounds of them belong to the sulfite esters.2. More compounds were collected by the continuous root exudates trapping system (CRETS) than the root soaking method (RS) and an increase in the hydrocarbon and amine compounds was observed in the solution prepared by the CRETS. More chemical compositions were detected by the resin plus extraction method than the direct extraction method and an increase in the alcohol and benzozic acid derivatives was observed in the solution prepared by the resin plus extraction method. The stability of root exudates can be maintained at a relatively lower temperature (35℃). It have more advantages in the analysis of the compounds in the Welsh onion root exudates when collect the Welsh onion root exudates by the CRETS and at a relatively lower temperature (35℃). 3. Volatile compounds in Welsh onion roots were extracted by static headspace (SHS) and identified by gas chromatography-mass spectrometry (GC-MS). The ether (thioether), alcohol (mercaptan), aldehyde, hydrocarbon, ester, acid, heterocyclic were detected in Welsh onion roots volatile compounds, most of these were organo-sulfur compounds. The major mono-thiosulphinates was methanethiol and propanethiol. The major di-thiosulphinates was disulfide dimethyl, disulfide methyl propyl and disulfide dipropyl. The major tri-thiosulphinates was dimethyl trisulfide and trisulfide dipropyl.4. The roots of’Yuanzang’have more volatile compounds than’Zhangqiu’, but there is little difference between the seedling stage and adult stage. During the extraction process of volatile compounds from Welsh onion roots, higher relative content of mercaptan and acids were got by cuting processing while more material were got by grinding treatment, in which the relative content of hydrocarbon and aldehyde compounds was higher.5. The seed germination and sprout growth of cucumber were promoted by root exudates at low concentration while suppressed at high concentration, and the allelopathy of’Yuanzang’ was stronger than’Zhangqiu’. Inhibitory effects on hypha growth and spore germination of Fusarium oxysporum f.sp. cucumerinum enhanced with increasing concentration of root exudates, and’Yuanzang’showed stronger effects than’Zhangqiu’.6. Hydrocarbon, alcohol, ether, phenol, naphthalene, aldehyde, ketone, acid, ester, amide, heterocyclic compounds were detected in Welsh onion root exudates, of which the heterocyclic, ester and amide compounds occupied higher proportion. The phthalate esters and benzothiazole derivatives have a higher relative content while p-cresol2,2’-methylenebis[6-tert-butyl-, benzyl benzoate, benzoic acid p-tolyl ester,2-(methylthio) phenyl isothiocyanate have a lower relative content, which were higher in’Yuanzang’than in ’Zhangqiu’.7. The sprout growth of cucumber were promoted by different pH extract fractions from Welsh onion root exudates while hypha growth of Fusarium oxysporum f.sp. cucumerinum were inhibited. The allelopathy of alkali fraction was strong, followed by acidic fraction and water-soluble fraction. The higher relative content compositions of alkali fraction were thiazole heterocyclic and ester compounds, and there were increased the relative content of21.88%of sulfur compounds and8.22%of amides as compared with acidic fraction and water-soluble fraction.8. Four different polarity organic solvents (ethyl acetate, ethyl ether, chloroform, butyl alcohol) were used to extracte Welsh onion root exudates. The sprout growth of cucumber were promoted by different organic solvents extract components while hypha growth of Fusarium oxysporum f.sp. cucumerinum were inhibited. The allelopathy of ethyl acetate extract component (A) was the strongest, which is the allelopathic advantage component. Further separate the allelopathic advantage fraction (A), the allelopathy of component separated by the80%ethyl acetate+20%ether (A-1) was the strongest, the A-1component identified by GC-MS have seven compounds of which were dibutyl phthalate, diisooctyl phthalate, diethyl phthalate,2-(methylthio) benzothiazole, benzothiazole, benzoic acid p-tolyl ester, cycluron.9. The sprout growth of cucumber were promoted by dibutyl phthalate and benzoic acid p-tolyl ester while hypha growth of Fusarium oxysporum f.sp. cucumerinum were inhibited. The allelopathy of dibutyl phthalate increased first and then decreased with the increasing of concentration, and the allelopathy of benzoic acid p-tolyl ester gradually increased. The seed germination and sprout growth of cucumber were promoted by benzothiazole at low concentration while suppressed at high concentration, the hypha growth of Fusarium oxysporum f.sp. cucumerinum were inhibited by benzothiazole, the inhibition increased first and then decreased. Change of amylase activity in cucumber cotyledon was in agreement with the tendency of sprout growth, the tendency of IAA oxidase activity in cucumber hypocotyl in reverse.