Further histological comparisons of black spot, physiological internal necrosis, black heart, and hollow heart in potatoes

Abstract

Necrotic cells of black heart, hollow heart and physiological necrosis show light to pronounced melanin discolorations of both protoplasmic contents and cell walls. In these respects they are comparable with necrotic cells of blackspot. In very early stages of black heart, and perhaps of all cellular necrosis, the discoloration is scarcely visible but the contents of the cells are granular-containing small ovoid bodies. Chlorogenic acid and tyrosine tend to accumulate in affected areas with tyrosine increasing the most in the inner parenchyma zones of the tuber. Wound phellogen is initiated early in the development of physiological necrosis and hollow heart in cells surrounding small necrotic patches. A complete internal wound periderm is formed in advanced hollow heart. Suberization of cell walls is pronounced in physiological necrosis and hollow heart, but appears to be much less characteristic of black heart. Cell wall thickening and increases in hemicelluloses and pectins occur in physiological necrosis, to some extent in necrotic centers of early hollow heart, but are less characteristic of black heart. Changes in the state and distribution of lipids occur in all three disorders. These preliminary observations stress the need for more comprehensive histological and histochemical information on physiological disorders of potatoes.