Coumaroyl-isocitric and caffeoyl-isocitric acids as markers of pineapple fruitlet core rot disease

Introduction - Fruitlet core rot is the major post-harvest disease affecting 'Queen' pineapple in La Reunion island. The symptoms are black spots located in the pineapple fruitlets. Materials and methods - Fusarium ananatum, the main causal agent of fruitlet core rot was inoculated in 'MD-2' and 'Queen' (Victoria), a tolerant and a susceptible cultivar, respectively. A metabolomics approach to healthy and inoculated fruitlets allowed to determine which putative metabolites are involved in fruitlet core rot disease. The evolution of fruitlet core rot was then followed-up with a focus on the phenolic compounds. Results and discussion - Based on the metabolomics results, the phenolic compounds seemed to be determining markers of black spots. Coumaroylisocitrate and caffeoylisocitrate dramatically increased in the infected fruitlets in both cultivars post-inoculation. The 'MD-2'-infected fruitlets reached higher hydroxycinnamic acid levels in a shorter time than those of the 'Queen'-infected fruitlets. In healthy fruits of 'MD-2', coumaroyl-isocitric acid and hydroxybenzoic acids were naturally produced as the fruit mature. Conclusion - These phenolic compounds play a major role in the pineapple disease resistance.