HISTOPATHOLOGY OF THE INTERACTION BETWEEN ASCOCHYTA-FABAE AND VICIA-FABA - COMPARISON OF SUSCEPTIBLE AND RESISTANT REACTIONS

Leaves of Vicia faba plants naturally or artificially infected with As cochyta fabae were examined using light, scanning and transmission ele ctron microscopy. Histological comparison was made of 1 resistant (29H ) line and 1 susceptible (48B) line to study possible differences in s ymptom expression, host-cell necrosis and extent of fungal development . In the susceptible line, 48B, a lesion consisted of a central necrot ic region where the fungus invaded intercellular spaces between the ep idermis and the mesophyll. Although no fungal hyphae were found in the surrounding region, many cells had collapsed. In the resistant line, 29H, the fungus failed to develop during penetration. The host cells u nderlying fungal spores became orange-brown and a hypersensitive react ion caused flecking lesions. In addition, the granal lamellae of chlor oplasts of the adjacent mesophyll cells were swollen and electron tran slucent. Necrotic lesions appeared in a few cases but remained limited . At the periphery of this lesion, many electron-dense bodies were att ached to the walls of mesophyll cells.