<![CDATA[Watermelon production is frequently constrained by soil-borne fungal diseases, particularly those caused by Fusarium fujikuroi, which have been shown to severely impair plant growth and productivity. The objective of this study is to isolate, identify, and evaluate the antifungal potential of Streptomyces strains associated with watermelon-growing soils and to explore their functional traits related to biological control. A total of 22 actinomycete isolates were recovered and screened for chitinolytic and antifungal activities, leading to the selection of three promising strains designated NVC-TL3, strain 4, and NVC-TX. Morphological characterization and 16S rRNA gene sequencing identified these isolates as Streptomyces cyaneochromogenes NVC-TL3, Streptomyces toxytricini strain 4, and Streptomyces lydicus NVC-TX. All strains exhibited extracellular chitinase activity and significantly inhibited the growth of *F. fujikuroi* under in vitro conditions. Among them, S. lydicus NVC-TX demonstrated the strongest antagonistic activity, achieving 74.9% mycelial growth inhibition after 7 days of incubation. The efficacy of the substances was further confirmed by greenhouse experiments, which demonstrated a reduction in disease severity to 14.9% and a significant enhancement in plant vigor in comparison to the pathogen-inoculated control. The study revealed substantial functional variation among phylogenetically distinct Streptomyces isolates and demonstrated a close association between chitinolytic capacity and disease suppression. These findings contribute to the existing body of knowledge concerning the biodiversity of Streptomyces associated with watermelon and highlight the potential of S. lydicus NVC-TX as a promising biological control agent. The application of this strain could contribute to the reduction of dependence on synthetic fungicides, thereby promoting environmentally sustainable disease management, and supporting healthier and more productive watermelon cultivation systems. ]]>
