Microemulsification of nonvolatile components of Melaleuca alternifolia and borneol can effectively defend Rhizoctonia solani

Abstract

The exploration of plant bioactive components for plant protection is significant for sustainable development of agriculture. Although the essential oil of Melaleuca alternifolia Maiden & Betche Cheel has been widely applied in many fields, its non-volatile active components are not fully utilized in agriculture. This study found that nonvolatile components of M. alternifolia possessed fungicidal activity against Rhizoctonia solani Kühn. The n-butanol extract of M. alternifolia mixed with borneol at a ratio of 5:1 enables good synergism in terms of antifungal activity. Importantly, the fungicidal activity against R. solani can be further significantly improved by microemulsification. The 10% microemulsion (ME) possessed significant preventive and curative efficacy against R. solani in rice plants with control efficacy of 85.29% and 76.87% at 300 mg/L, respectively. They are comparable to the control efficacy of 8% validamycin A aqueous at 300 mg/L. The 10% ME could also suppress the formation of sclerotia of R. solani even at a low concentration of 50 mg/L. Primary study on the mechanism of action indicated that 10% ME destroyed the cell membrane and mitochondria, triggered the release of cellular contents, produced reactive oxygen species (ROS) and reduced the number of cell nuclei in R. solani mycelia. This study demonstrates that the nonvolatile components of plants are valuable resources for the development of plant-source green formulations for the control of phytopathogenic bacteria and fungi.