Vinegar residue compost as a growth substrate enhances cucumber resistance against the Fusarium wilt pathogen Fusarium oxysporum by regulating physiological and biochemical responses

Fusarium wilt caused by the fungus Fusarium oxysporum f. sp. cucumerinum (FOC) is the most severe soil-borne disease attacking cucumber. To assess the positive effects of vinegar residue substrate (VRS) on the growth and incidence of Fusarium wilt on cucumber, we determined the cucumber growth parameters, disease severity, defense-related enzyme and pathogenesis-related (PR) protein activities, and stress-related gene expression levels. In in vitro and pot experiments, we demonstrated the following results: (i) the VRS extract exhibited a higher biocontrol activity than that of peat against FOC, and significantly improved the growth inhibition of FOC, with values of 48.3 %; (ii) in response to a FOC challenge, antioxidant enzymes and the key enzymes of phenylpropanoid metabolic activities, as well as the PR protein activities in the roots of cucumber, were significantly increased. Moreover, the activities of these proteins were higher in VRS than in peat; (iii) the expression levels of stress-related genes (including glu, pal, and ethylene receptor) elicited responses to the pathogens inoculated in cucumber leaves; and (iv) the FOC treatment significantly inhibited the growth of cucumber seedlings. Moreover, all of the growth indices of plants grown in VRS were significantly higher than those grown in peat. These results offer a new strategy to control cucumber Fusarium wilt, by upregulating the activity levels of defense-related enzymes and PR proteins and adjusting gene expression levels. They also provide a theoretical basis for VRS applications.