PURPLE TOP AS A CAUSE OF POTATO CHIP DISCOLORATION

Abstract

ABSTRACT Purple top (PT) a disease in potatoes. Solarium tuberosum L. caused by the aster yellows mycoplasma-like organism (AY-MLO) was shown to cause chip browning in processed potatoes. PT was produced in field experiments from 1984-1987, in which infective aster leafhoppers were caged on plants of the potato cvs. Monona and Norchip. Tubers from these plots, tubers from plants exposed to non-infective leafhoppers, and tubers from non-caged controls were harvested, stored, and samples were chipped at monthly intervals. Chips from PT-infected tubers appeared normal until about the January-February processing when dark discoloration occurred in the area of the vascular ring. In March through June chippings, the brown discoloration had spread and intensified in chips in the medullary and cortical areas of chips. Chips from tubers of plants exposed to healthy aster leafhoppers and from tubers from non-caged plants, on average, retained a bright color. The browning was similar in chips obtained from PT-infected tubers stored at 9° or 11° C and may be due to excessive accumulation of reducing sugars resulting in non-enzymatic browning.