Abstract: 【Objective】The systemic long-lasting and broad-spectrum resistance of cucumber seedlings was induced with natural or synthetic compounds. The objective of this study is to shed light on the resistance induced by fluoro-substituted benzothiadiazole derivatives (FBT) to cucumber Fusarium wilt and provide data for elucidating its mechanism.【Method】Before transplanting, 50 mg·L^-1 of FBT was used to spray so as to induce the cucumber seedlings at 3-4 true leaf stage. Three days later, the cucumber seedlings were transplanted into the soil with Fusarium oxysporum f. sp. cucumerinum Owen, and sprayed with FBT so as to induce resistance for the second time. Sequently, the cucumber seedlings were sprayed every 7 days and for 3 times continuously. Meanwhile, contrast agent BTH also was used with the same induction method and 70% thiophanate-methyl at 1 500 times was applied through root-irrigation. The efficiency on the blight disease resistance was assessed through investigating disease index. For studying the influence of FBT on F. oxysporum f. sp. cucumerinum invasion of cucumber, the cucumber’s radicle length was sprouted to 0.5 cm and then the radicle immersed in 50 mg·L^-1 of FBT. The resistance of cucumber seedlings was induced another time at the stage of 2 pieces of leaves. Since then, the cucumber seedlings were sprayed in order to induce the resistance every 7 days and total for 3 times. Twenty-four hours after the last induction, cucumber was inoculated with F. oxysporum f. sp. cucumerinum by the root-drenching method. Treated roots and the controls were harvested at 1, 3, 5, 7, 9, 11, 14, 16, 20, 24 and 29 days after inoculation and then cleaned in ice water. After induction, acid fuchsin dyeing technology was used to evaluate the FBT impacts on fusarium infection. In addition, the Maule reaction and toluidine blue staining technique were used to evaluate the change of lignin and phenolic substances in cucumber root tissue deposition. Moreover, metabolic alterations were investigated and enzyme activities of HRGP and β-1,3-glucanase were determined to analyze the physiological changes in BTH-treated cucumber by speetropho tometer-chromatometry.【Result】Because of the expression of induced resistance, it was found that the control efficiency of FBT was 62.01% at concentration of 50 mg·L^-1, higher than BTH treatment and thiophanate-methyl treatment at the same conditions. Seven days after inoculation, colonization of F. oxysporium f. sp. cucumerinum began to appear in the cucumber root tissue induced by FBT. Whereas a large number of hyphae and spores had appeared on the cucumbers not induced with FBT, it indicated that cucumber induced with FBT could gain resistance so as to surpresse the colonization of pathogens. The brown lignin was accumulated in the cucumber roots induced by FBT, especially in epidermal cell walls and phloem xylem. Observation of phenolic substances showed that, two days after FBT induction, phenolic compounds appeared in 4 and 6 days, fluorescence signal in root tissue stronger, phenolic accumulated. Eight days after induction, the phenomena that root tissue fluorescence signal disappeared, phenolic no deposition, lignin and phenolic compounds accumulation increased, resulted in the enhancement of the resistance of the cell wall.【Conclusion】It was found that the resistance induced in cucumber seedlings by FBT includes the accumulation of secondary metabolites in the root and the activation of disease-resistant proteins, suggesting FBT is a promising novel inducer.

Key words: fluoro-substituted benzothiadiazole derivatives, Fusarium oxysporum f. sp. cucumerinum Owen, induced resistance, ultrastructure, soil-born disease