Induction of the Phenylpropanoid Pathway by Acibenzolar-S-Methyl and Potassium Phosphite Increases Mango Resistance to Ceratocystis fimbriata Infection

This study used both microscopic and biochemical analyses to investigate the possible defense responses induced by acibenzolar-S-methyl (ASM) and potassium phosphite (Phi) in mango plants inoculated with Ceratocystis fimbriata. Disease development was evaluated in the stems of inoculated mango plants and these were examined using fluorescence and light microscopy. High-performance liquid chromatography (HPLC) was used to quantify secondary metabolites in the stem sections. Spraying the plants with ASM and Phi reduced internal necrosis and disease development. The ASM and Phi induced many microscopic defense responses in the stem tissues against C. fimbriata infection. HPLC analysis revealed that the concentrations of two alkaloids (theobromine and 7-methylxanthine) and 10 phenolic compounds (catechin, epicatechin, epigallocatechin, gallic acid, myricetin, p-coumaric acid, p-hydroxybenzoic acid, phloridzin, sinapinic acid, and salicylhydroxamic acid) were higher in the stem tissues of plants sprayed with ASM or Phi than in inoculated control treatment. The concentrations of phenolic compounds were higher in the stem tissues of inoculated plants than in noninoculated plants, while the inverse was observed for alkaloids. Higher concentrations of secondary metabolites in the stem tissues were detected in the early stages of fungal infection, especially in plants treated with inducers. Taken together, the results from the present study clearly support the concept that the phenylpropanoid pathway in the stem tissues of mango plants infected by C. fimbriata can be induced by ASM and Phi.