Debaryomyces hansenii, Stenotrophomonas rhizophila, and Ulvan as Biocontrol Agents of Fruit Rot Disease in Muskmelon (Cucumis melo L.)

The indiscriminate use of synthetic fungicides has led to negative impact to human health and to the environment. Thus, we investigated the effects of postharvest biocontrol treatment with Debaryomyces hansenii, Stenotrophomonas rhizophila, and a polysaccharide ulvan on fruit rot disease, storability, and antioxidant enzyme activity in muskmelon (Cucumis melo L. var. reticulatus). Each fruit was treated with (1) 1 × 106 cells mL−1 of D. hansenii, (2) 1 × 108 CFU mL−1 of S. rhizophila, (3) 5 g L−1 of ulvan, (4) 1 × 106 cells mL−1 of D. hansenii + 1 × 108 CFU mL−1 of S. rhizophila, (5) 1 × 108 CFU mL−1 of S. rhizophila + 5 g L−1 of ulvan, (6) 1 × 106 cells mL−1 of D. hansenii + 1 × 108 CFU mL−1 of S. rhizophila + 5 g L−1 of ulvan, (7) 1000 ppm of benomyl or sterile water (control). The fruits were air-dried for 2 h, and stored at 27 °C ± 1 °C and 85–90% relative humidity. The fruit rot disease was determined by estimating the disease incidence (%) and lesion diameter (mm), and the adhesion capacity of the biocontrol agents was observed via electron microscopy. Phytopathogen inoculation time before and after adding biocontrol agents were also recorded. Furthermore, the storability quality, weight loss (%), firmness (N), total soluble solids (%), and pH were quantified. The antioxidant enzymes including catalase, peroxidase, superoxide dismutase, and phenylalanine ammonium lyase were determined. In conclusion, the mixed treatment containing D. hansenii, S. rhizophila, and ulvan delayed fruit rot disease, preserved fruit quality, and increased antioxidant activity. The combined treatment is a promising and effective biological control method to promote the shelf life of harvested muskmelon.