Cucumber Fusarium wilt resistance induced by intercropping with celery differs from that induced by the cucumber genotype and is related to sulfur-containing allelochemicals

Abstract

Fusarium wilt is a serious soil-borne disease for cucumber production; however, intercropping with celery and using resistant cultivars could alleviate this problem. The aims of the study were to verify whether cucumber Fusarium wilt resistance induced by intercropping with celery differs from that induced by the cucumber genotype and whether celery synthesizes organosulfur allelochemicals to inhibit the growth of Fusarium oxysporum f. sp. cucumerinum (Foc). First, biochemical and transcriptome analyses were performed for the roots of two cucumber cultivars during the response to Foc infection in a monoculture system and cucumber/celery intercropping system, and the results indicated that the Fusarium wilt-resistant cucumber cultivar and cucumber intercropped with celery resulted in different immune responses against Foc inoculation. Then, the possible allelochemicals in the fresh root and rhizosphere soil of celery were extracted with acetone, separated and purified by chromatography four times and cocultured with Foc in vitro. Three organosulfur compounds, namely, thioglycolic acid, propanethiol and isopropyl isothiocyanate, were identified from the chromatography fractions, with the highest inhibition on Foc in the fourth chromatography by gas chromatography/mass spectrometry. All these compounds exhibited inhibitory effects on Foc, but thioglycolic acid showed stronger inhibition than the other two compounds and completely inhibited the growth of Foc colonies at concentrations of 50–100 μmol L−1. The information obtained will permit new management practices that prevent and control cucumber Fusarium wilt.