Streptomyces spp. as an antagonistic agent against Fusarium spp. in poblano pepper cultivation (Capsicum annuum)

ABSTRACT Background/Objective. Pepper wilt is one of the diseases affecting the production and quality of chili pepper (Capsicum annuum) crops, causing losses of over 60% globally. Controlling this disease with synthetic fungicides has limitations in terms of effectiveness. Strains of Streptomyces that act as antagonists to phytopathogenic fungi represent a potential alternative. The objective was to analyze the performance of Streptomyces spp. in reducing the incidence of the disease in poblano chili plants under field conditions. Materials and Methods. Poblano-type chili seedlings (variety AP-VR) were transplanted into soil naturally infested with Fusarium spp. Four treatments were applied via soil drench: Streptomyces lasiicapitis (B22) and S. neyagawaensis (B31) (at a concentration of 1 × 10⁸ CFU mL⁻¹ for each strain), a chemical control [TCMTB (1.75 mL L⁻¹), dimethomorph (3.5 mL L⁻¹), and thiophanate-methyl (1.75 g L⁻¹)], and an absolute control (water). The experiment followed a randomized complete block design with three replicates, each consisting of 60 plants. The variables evaluated were the incidence of wilt and the number of colony-forming units (CFU) of the fungus in the soil, assessed across four sampling events. The experiment was conducted in 2024 and 2025. Results. Compared to the absolute control, the incidence of wilt caused by Fusarium spp. was 22.6 and 29.3% lower in chili plants inoculated with S. lasiicapitis (B22) in 2024 and 2025, respectively; meanwhile, in plants inoculated with S. neyagawaensis (B31), the incidence was 27 and 35.6% lower in 2024 and 2025, respectively. Furthermore, plants inoculated with B22 showed an incidence of 6–8%, while the incidence for plants inoculated with B31 was 10.5 and 14.2% lower than that of the chemical control in 2024 and 2025, respectively. The reduction rate of Fusarium spp. CFU (colony-forming units) was higher with B31 than with B22 in 2024, although no statistically significant difference was observed between the two strains in either of the years evaluated. The difference in Fusarium spp. CFU content in the soil between the Streptomyces spp. treatments (B22 and B31) and the absolute control was 98.6% in 2024 and 91% in 2025. Conclusion. Streptomyces spp. demonstrated a greater reduction in Fusarium spp. CFU content in the soil (91–98%) compared to the chemical treatment (50–58.33%), as well as a lower disease incidence (22.6–35.6%). The field experiment, conducted over two agroclimatically distinct years, demonstrated that S. neyagawaensis reduced disease incidence, even under conditions that favored the proliferation of Fusarium spp. Based on these results, S. neyagawaensis emerges as a significant biocontrol agent that also contributed to increased earliness and yield (34–36 t ha⁻¹) in poblano peppers.