The association of copper with tyrosinase activity and internal discoloration (blackspot) in Russet Burbank potatoes

Abstract

During 1964 and 1965, field and laboratory studies were conducted to determine if copper was associated with susceptibility to blackspot. When the copper content of tubers was increased by CuSO4 · 5H2O soil drenches, no change in intensity of discoloration or tyrosinase activity was found. However, when chelated copper was sprayed on plants, tyrosinase activity was decreased even though the copper content of the tuber tissue was increased more than three times that of the control. When the copper content of several lots of tubers, both susceptible and resistant to blackspot, was determined, it was found that tissue from the stem end of resistant tubers was higher in copper than that of stem-end tissue from susceptible tubers. Also, tissue at the bud end, where blackspot blemishes rarely occurred, was found to contain nearly one and one-half times as much copper as susceptible stem-end tissue. Tissue taken from Red Pontiac, a very blackspot resistant variety, contained more than two times as much copper as the most susceptible Russet Burbank stem-end tissue. These studies showed that copper content was not directly associated with blackspot susceptibility. In fact, the data suggest that copper content may be associated with resistance.