Colony Development of the Powdery Mildew on Susceptible and Resistant Varieties of Barley

Abstract

Observations were made on the colony development of Erysiphe graminis hordei on varieties of barley, using entire inoculated leaves, after fixing and clearing in formalin-acetic-alcohol and staining with acid Fuchsin.
On susceptible varieties, the hyphae usually grow along the periclinal lines of epidermis and form a colony of rectangular, finally elliptic, periphery. About six days after inoculation, conidium formation begins at the center of the colony and later it extends to the margin. There appear convolute hyphae at the margin of the colony along the long axis; these hyphae, developing less appressoria and haustoria in number than the ordinaly hyphae, do not generally adhere tightly to the leaf surface. On comparatively resistant varieties, thin colonies of triangular, semi-circular, shovel-like or dumbbell form in shape, are commonly found. At an earlier stage of colony growth than the cases on susceptible varieties, conidia and convolute hyphae were often produced. Conidium formation, however, was sparse in accordance with the poor development of hyphae. Browning of host tissues beneath the infection court were frequently observed.