Efficacy of Organic-Based Substrate Formulation of Bacillus Strains and Trichoderma asperellum Against Fusarium Wilt of Cashew

Abstract

Biological control has emerged as a leading approach in managing crop diseases including Fusarium wilt of cashew caused by Fusarium oxysporum f.sp. anacardi. However, this approach is limited by the high cost of commercially available growth media and ultimately lacks applications at the farmer's level. The study examined three organic-based substrate formulations (rice bran, rice husk and their combination) of four combined Bacillus strains (Bacillus subtilis 4/5021 and Bacillus velenzesis 10/5140, 11/A + 1 and 13/A + 3) or Trichoderma asperellum to control the disease. The experiments were conducted in farmers' fields in 2021/2022 and 2022/2023. The treatments were applied once during the rainy season by soil drenching at a rate of 20 mL of bioformulation per litre of water around each tree. The results revealed that the treated cashew trees had significantly (p ≤ 0.05) lower final disease severity (between 15.17% and 33.75% in 2021/2022 and 14.43%–31.93% in 2022/2023) than the untreated trees (77.17% and 89.31%, respectively). The only treatment that was not significantly different from the control was the rice husk–T. asperellum formulation in both years. In treated plots, disease severity decreased over time each year, whereas disease severity increased in untreated trees. Based on these results, the three formulations of Bacillus strains and two of the Trichoderma asperellum formulations (bran-based or bran–husk combination) should be evaluated further for the management of Fusarium wilt of cashew. This study offers a potential solution to utilise locally available organic substrates for developing liquid-based formulations of biological control agents.