LC-MS Analysis of Phenolic Compounds in Tubers Showing Zebra Chip Symptoms

A new potato disorder called Zebra Chip (ZC) has been identified in the United States and has been especially problematic in Texas, where substantial economic losses have been incurred. Upon frying, ZC tubers develop a dark “zebra” pattern of discoloration. LC-MS analysis of methanolic extracts from symptomatic tubers revealed major alterations in aromatic amino acids and phenolic compounds. Tyrosine concentrations increased over 8-fold in some symptomatic tubers, reaching up to 3 mg/g DW; This increase may be a major component of the browning of ZC tubers. No marked differences in chlorogenic acid concentrations were found, but differences in other caffeoyl derivatives, including caffeoylpolyamines, were observed. Salicylic acid, a key regulator of plant defenses, was present at very high concentrations in ZC tubers, which is consistent with what would be expected from tubers mounting a defense response to a pathogen. ZC tubers may be a useful model to study how certain plant-microbe/pest or plant-environment interactions affect tuber physiology.