Adaptive Agriculture Resilient Innovations for Sustainable C

Biocontrol Approach by Combining Antagonistic Bacteria and Organic Materials Against Diaporthe destruens Juniarti Mawarni Sari ¹ , Makoto Ikenaga* 2 ¹ Graduate School of Agriculture, Forestry and Fisheries, Kagoshima University, Japan ² Research Field in Agriculture, Agriculture, Fisheries and Veterinary Medicine Area, Kagoshima University, Japan *Corresponding author’s email: ikenaga@agri.kagoshima-u.ac.jp 4 Abstract Sweet potato foot rot disease, caused by Diaporthe destruens, is a major factor that significantly reduces both the yield and quality of sweet potatoes, especially in Kagoshima Prefecture, Japan. To address this issue, our study focused on isolating and testing antagonistic bacteria as a biocontrol approach. In previous research, we isolated several bacterial strains from the infected soil of a sweet potato field treated with organic materials. The isolation was guided by meta-16S sequencing data to identify potential antagonistic bacteria against D. destruens. Among these isolates, strains SF11 and SF29 showed strong antagonistic activity and were identified as Streptomyces rubellomurinus and Kitasatospora misakiensis, respectively. Based on these results, we hypothesized that combining antagonistic bacteria with organic materials could produce a collaborative biocontrol effect to suppress the growth of D. destruens. To evaluate this hypothesis, microbial materials of strains SF11 and SF29 were prepared and applied to field soil pretreated with two types of organic materials, with chemical fertilizer serving as the control. The field experiment consisted of three treatments: both bacterial strains, either strain alone, or neither strain. The microbial materials were applied at a concentration of 3 × 10 ⁶ CFU/g for each treatment, and plant growth was monitored throughout the cultivation period. No early growth inhibition was observed in any treatment, indicating that the combination of organic and microbial materials is safe for initial plant development. Overall, the combination of antagonistic bacteria with the organic amendments is expected to inhibit the infection of D. destruens in the late-growing stages. Keywords : sustainable agriculture, crop production, soil fertility, climate resilience, agroecology Webinar Seminar: Adaptive Agriculture: Resilient Innovations for Sustainable Change Date: 7 November 2025 | Time: 09.00 – 12.00 (Thai Time) Hosted: Faculty of Technology and Community Development, Thaksin University, Thailand