Physiological disorders of the apple at mid-season stage of development

Abstract

Morphological and anatomical development of epidermis, hypodermis and cortical cells in relation to cuticle on young developing apples were observed by scanning electron microscopy (SEM). Initial symptoms of abnormal cell development appeared in the orchard at approximately mid-season growth as depressions on the fruit surface. They were observed on the calyx or basin areas, light-reddish brown in color with a light-greenish margin. Normal fruit tissue was covered by a well-defined, uniform cuticle subtended by an epidermis contiguous to 10–12 layers of hypodermal cells. In areas where anthocyanin development was evident, collapse and fragmentation of cortical cells extended deep within the cortex nearly to the core-line bundles. The cuticle was thin, subtended by fragmented thick-walled hypodermal cells; however, cuticle thickening occurred at the edge of the tissue fissure. Cell senescence was indicated by extreme cell-wall thickening in the hypodermis. The fruit was incapable of further growth expansion in the affected area, as a result of cell collapse.