High Chlorogenic and Neochlorogenic Acid Levels in Immature Peaches Reduce Monilinia laxa Infection by Interfering with Fungal Melanin Biosynthesis

Chlorogenic acid (CGA) and its isomer, neochlorogenic acid (NCGA), were found to be the major phenolic compounds in the flesh and peel of three peach cultivars. Their concentrations are especially high in immature fruits (CGA, 151−548 mg/kg; NCGA, 85−380 mg/kg), whose resistance to the brown rot fungus, Monilinia laxa, is very high. The concentrations of these two phenolic compounds decline in maturing fruits (CGA, 77−181 mg/kg; NCGA, 30−82 mg/kg), and this decline is associated with a concomitant increase in susceptibility to brown rot infection. Other phenolic compounds found in the same HPLC chromatograms at 340 nm from each peach extract at varying sampling dates in each of the three peach cultivars were not correlated with the incidence of brown rot and appeared only in some cultivars. The incidence of brown rot for each cultivar at each sampling date was significantly negatively correlated with the NCGA (r > −0.85) and CGA (r > −0.90) contents. At concentrations that are similar to those in peach fr...