Effects of Melatonin and Bacillus amyloliquefaciens MPA 1034 on the Postharvest Quality of Potato Tubers

Fusarium oxysporum is the causal agent of Fusarium dry rot disease (FDR), which results in postharvest potato losses. Biological control agents (BCAs) and phytohormone melatonin have antifungal effects on fungal pathogens and can be used as alternatives to synthetic chemical fungicides. The aim of the study was to evaluate the integrated effects of melatonin (MEL) and Bacillus amyloliquefaciens (Bamy) on the postharvest quality of potato tubers. Bamy was integrated with six MEL concentrations and screened against F. oxysporum in vitro and in vivo. The effects of the best performing treatment were evaluated for antioxidant activity, phenolic content, ascorbic acid content, and protein content on potato tubers. In the in vitro screening trial, treatment with Bamy + MEL100 had the highest mycelial growth inhibition percentage (59.92%), followed by Bamy + MEL15 and Bamy + MEL50 (56.12% and 55.27%, respectively). Potato tubers treated with Bamy + MEL100 had the lowest disease severity of FDR (50.61%) and a pathogen penetration value of 6.39 mm. Bamy + MEL50 showed a disease severity percentage of 59.72%. The exogenous application of melatonin at a concentration of 100 µM combined with B. amyloliquefaciens was the most effective treatment with the highest phenolic content (144.1 mg GAE/g DW) and protein content (68 mg/g DM) compared to the untreated tubers (104.4 GAE/g DW phenolic content and 50.06 mg/g DM protein content). Tubers treated with melatonin had the highest ascorbic acid content (5.48 mg AAE/100g DM) compared to the untreated tubers (4.09 mg AAE/100 g DM). Overall, tubers treated with a combination of melatonin and B. amyloliquefaciens showed less severe symptoms of FDR across all concentrations. Based on these findings, it can be concluded that B. amyloliquefaciens and melatonin at 100 µM concentration can be used in combination to inhibit the growth of F. oxysporum.