OBSERVATIONS ON THE INFECTION OF COX'S ORANGE PIPPIN APPLES BY GLOEOSPORIUM PERENNANS ZELLER & CHILDS

Conidia of Gloeosporium perennans germinating on the surface of Cox's Orange Pippin apples in the orchard, produce a germ tube which generally swells to form a thick-walled appressorium. If the underlying tissues are not suberized the appressorium then produces an infection thread which penetrates the wall of the epidermal cell. If the underlying tissue is suberized no infection thread is formed. Subsequent rotting takes place either by penetration via a point of weakness in the suberized layer of cells across the lenticel as in Cox's Orange Pippin or by direct invasion of this layer as in the variety Sunset. Some lenticels have been observed where the suberized layer has not formed. Fruit infected in August and September rots at a greater rate than fruit infected in June and July of the same year. In years when susceptibility to rotting is high, infections initiated in July may develop more rapidly than those initiated later in the season in a year when susceptibility to rotting is relatively low. The rate of rotting has been found to increase with the size of fruit.