Dimethyl trisulfide (DMTS) fumigation enhances fruit quality and reduces postharvest incidence of bacterial canker in tomato

Bacterial canker of tomato, caused by Clavibacter michiganensis subsp. michiganensis (Cmm), is a major postharvest disease. The prevention and control of this disease are major challenges in tomato production. Dimethyl trisulfide (DMTS) is a sulfide-based volatile compound produced by several plant species and reported to have antifungal activity. In the present study, the ability of DMTS fumigation to control bacterial canker of tomato and the underlying mechanism of action were investigated. DMTS fumigation effectively inhibited Cmm growth and altered its morphology and membrane structure as observed at 4 dpi. DMTS significantly inhibited biofilm formation (58.6 %) and exopolysaccharide secretion (73.5 %) by Cmm. The EC50 value of DMTS was approximately 1.0 μg/L. However, the inhibitory effect of DMTS did not increase at concentrations > 1.0 μg/L. DMTS at 1.0 μg/L inhibited the transcription of pathogenicity-related genes (celA, pat-1, chpC, and sbtA) in Cmm. DMTS fumigation significantly inhibited Cmm infection in wound inoculated tomatoes assessed at 1-, 3-, 5-, and 7-day intervals. Notably, the fruit wounds exhibited minimal disease symptoms at 7 dpi. DMTS fumigation treatment of Cmm resulted in a significant reduction in the biomass of Cmm at 7 dpi. Regarding fruit quality, DMTS fumigation of harvested tomatoes decreased weight loss, disease incidence, and the disease index in tomato fruits and maintained a higher degree of fruit hardness and peel firmness at 7 dpi, relative to untreated fruit. Interestingly, DMTS significantly increased the level of ascorbic acid (an antioxidant), total soluble solids, total soluble sugars, ascorbic acid, and titratable acidity. The DMTS treatment also inhibited ethylene (ET) biosynthesis in tomato fruits at 7 dpi. The transcription of genes in the ET biosynthetic pathway (ACS2, ACS4, and ACO1) and ET-responsive genes (CBF1 and ERF1) was significantly inhibited by the DMTS treatment at 7 dpi. Our results indicate that DMTS fumigation effectively controls postharvest bacterial canker of tomato by increasing the level of ascorbic acid (a potent antioxidant) and inhibiting ET synthesis in tomato fruits.