COMPARISON OF MALUS INFECTION BY THE PATHOGEN ERWINIA-AMYLOVORA AND COLONIZATION BY THE SAPROPHYTE ERWINIA-HERBICOLA BY ELECTRON-MICROSCOPY

Erwinia amylovora infection of either apple stem or leaf tissue result ed in xylem occlusion by a fibrillar matrix material, determined by Th iery's thiocarbohydrazide (TCH) test to be the extracellular polysacch aride from E. amylovora. Plasmolysis of the xylem-parenchyma was also detected and was most likely a result of a toxin produced by the patho gen. This plasmolysis resulted in the collapse and death of the cell. An Erwinia herbicola isolate which had previously expressed inhibitory effects on E. amylovora was contained at the site of inoculation.