Ultra-High Performance Liquid Chromatography-Tandem Mass Spectrometry Identification of Metabolites in Winterberry Fruit Putatively Associated with Natural Disease Resistance to Diaporthe ilicicola.

Abstract

Winterberry holly (Ilex verticillata) is an ornamental plant popularly used in landscape design and sold as cut branches for fall and winter seasonal decoration. Latent fruit rot of winterberry is an emerging disease caused by the fungus Diaporthe ilicicola, which can result in up to 100% crop loss. Diaporthe ilicicola infects open flowers in spring, but symptom onset does not occur until the end of the growing season when the fruit is fully mature. This study was conducted to identify compounds displaying significant variation in abundance during fruit maturation and that may be putatively associated with natural disease resistance observed when the fruit is immature. Winterberry 'Sparkleberry' fruits collected at four timepoints during the 2018 and 2019 seasons were extracted in methanol and analyzed using high resolution ultra-high performance liquid chromatography-tandem mass spectrometry. The results showed a distinct separation of metabolic profiles based on fruit phenological stage. The top 100 features that were differentially expressed between immature and mature fruit were selected from both electrospray ionization (ESI) (-) and ESI (+) datasets for annotation. Eleven compounds shown to decrease throughout the season included cinnamic acids, a triterpenoid, terpene lactones, stilbene glycosides, a cyanidin glycoside, and a furopyran. Nine compounds shown to accumulate throughout the season included chlorogenic acid derivatives, hydrolysable tannins, flavonoid glycosides, and a triterpene saponin. Future research will further confirm the exact identity of the compounds of interest and determine whether they are biologically active toward D. ilicicola or I. verticillata. The results could inform breeding programs, chemical management programs, and novel antifungal compound development pipelines.