Reticine A, a new potent natural elicitor: isolation from the fruit peel ofCitrus reticulateand induction of systemic resistance against tobacco mosaic virus and other plant fungal diseases

Background Systemic acquired resistance (SAR) induced by elicitors is a highly satisfying form of resistance that protects plants against invading pathogens. Exploration and development of new elicitors is a promising alternative to conventional biocides in resistant pest management. In our previous broad screening, fruit peel extract ofCitrus reticulataBlanco exhibited the ability to induce SAR in tobacco. Result A new potent elicitor reticine A was isolated from the fruit peel extract of industrial cropC. reticulateand its structure was well elucidated.In vivoassays showed that reticine A had considerable control efficacies at 100 and 500 mu g mL(-1), being superior to commercial elicitor benzothiadiazole (BTH) (100 mu g mL(-1)). Reticine A had no significant impact on the virulence of tobacco mosaic virus (TMV) particles underin vitroconditions. Application of reticine A induced a local hypersensitive reaction (HR), systemic accumulation of H(2)O(2)and salicylic acid (SA), systemic increase in defensive enzyme activities and systemic upregulated expression of pathogenesis-related (PR) proteins, suggesting its induction of SAR in tobacco. The expression ofNPR1and SA biosynthesis genesICSandPALwere systemically upregulated. Conclusion SAR induced by reticine A against TMV in tobacco was demonstrated and the mechanism might be attributed to activating the expression of several defensive genes mediated by an SA signal. This study highlights the potential of reticine A which is recommended to be applied directly or as an active ingredient in the crude extract formulation ahead of time in the field, as well as being a potential lead compound for further optimization.