Abstract: The allelopathy of welsh onion root exudates collected by continuous root exudates trapping system（CRETS）was studied on cucumber seed germination and Fusarium oxysporum f. sp. cucumerinum，and the components of the root exudates were identified by gas chromatography-mass spectrometry（GS–MS）. The results showed that the seed germination and sprout growth of cucumber were promoted by root exudates of welsh onion at low concentration while suppressed at high concentration，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’. Heterocyclic，ester，amide，acid，hydrocarbon，aldehyde，ketone，phenol，alcohol，ether，naphthalene compounds were detected in root exudates of Welsh onion，of which heterocyclic，ester and amide were the most compounds. Phthalate esters and benzothiazole derivatives had greater relative contents while p-cresol 2,2’-methylenebis 6-tert-butyl-，benzyl benzoate，benzoic acid p-tolyl ester，2-（methylthio）phenyl isothiocyanate had lower relative contents，which were higher in‘Yuanzang’than in‘Zhangqiu’.

Key words: welsh onion, cucumber, root exudate, allelopathy, Fusarium oxysporum f. sp.cucumerinum