Development of Tetramycin-loaded Core-Shell Balls with Hot/Wet-Response Releasing Property for the Control of Bacterial Wilt Disease

Abstract

Ralstonia solanacearum is the pathogen responsible for Ralstonia solanacearum, which is soil-borne, infests plant conduits to cause disease.They are not easy to control and are harmful.Therefore the development of a controlled-release agent responsive to the pathogen's soil temperature and moisture conditions could aid in its control. Corn kernel powder is used as a carrier for Tetramycin biopesticide, with various compounds tested for bonding.They were then made by extrusion moulding.Temperature and wetness responsive components, including Pentaerythritol Tetrastearate, Pentaerythritol Tetraoleate, Polyethylene Glycol Stearate, and Polyethylene Glycol Monooleate,are compounded and coated onto Tetramycin cores to form an intermediate shell layer. Finally, Ethyl cellulose(EC)and Hydroxypropyl methyl cellulose(HPMC) are dissolved and sprayed onto the outermost layer to complete the pellet's shell layer.After the evaluation of texture performance test,DSC analysis,TG test,temperature and humidity response performance test, as well as pellet cross-section SEM observation, field effectiveness test, etc., the preferred formulations were screened.The results showed that the preferred Core formulation:Corn kernel powder:Tetramycin aqueous:Xanthan gum mass ratio=13.5:23:2; Intermediate Shell layer:PETS: PETO: PEG400MO mass ratio=10:30:10; and Outer Shell layer: Ethyl cellulose (EC):Hydroxypropyl methyl cellulose (HPMC) mass ratio=5:1.Under soil conditions of high incidence of Ralstonia solanacearum, i.e., sustained warmth (30-35℃) and high humidity (30% moisture content), the formulated pills showed a release rate of 95.18% to 96.24% over a period of 35 days. Moreover, they showed a stepwise cyclic release process under alternating warm and humid-dry and cold conditions.In field tests on tobacco, a relative preventive efficacy of 54.74% was achieved 106 days post-transplanting. Soil bacterial community structure analysis revealed a significant decrease (2.28-2.84 times) in the abundance of Solanaceae Raelia under Tetramycin pellet treatment compared to the control. Additionally, fungal community structure showed highter consistency initially across various soil depths, with diversity differences between soil layers reestablished later (106 days), while the predominant categories of bacteria and fungi remained unchanged.In this study, we successfully developed a nucleoshell-type slow-controlled release pill embedded with Tetramycin. This pill effectively responded to temperature and humidity changes, resulting in high efficacy in disease prevention.This development holds significant promise for effectively improving drug utilization and easing application challenges, offering broad prospects for Ralstonia solanacearum prevention and control in agriculture.