This research shows that two plant compounds, melatonin and methyl jasmonate, work together to protect watermelon plants from a devastating fungal disease called Fusarium wilt. When applied to plant roots at specific concentrations, these compounds activate the plant’s natural defense mechanisms and directly slow down fungal growth. Importantly, the two compounds enhance each other’s effects, creating a protective cycle that makes the plant significantly more resistant to infection, offering a natural alternative to chemical pesticides.