Histopathology of the interaction between Ascochyta fabae and Vicia faba: comparison of susceptible and resistant reactions

Abstract

— Leaves of Vicia faba plants naturally or artificially infected with Ascochyta fabae were examined using light, scanning and transmission electron microscopy. Histological comparison was made of 1 resistant (29H) line and 1 susceptible (48B) line to study possible differences in symptom expression, host-cell necrosis and extent of fungal development. In the susceptible line, 48B, a lesion consisted of a central necrotic region where the fungus invaded in- tercellular spaces between the epidermis and the mesophyll. Although no fungal hyphae were found in the surround- ing region, many cells had collapsed. In the resistant line, 29H, the fungus failed to develop during penetration. The host cells underlying fungal spores became orange-brown and a hypersensitive reaction caused flecking lesions. In addition, the granal lamellae of chloroplasts of the adjacent mesophyll cells were swollen and electron translucent. Necrotic lesions appeared in a few cases but remained limited. At the periphery of this lesion, many electron-dense bodies were attached to the walls of mesophyll cells.