Vegetative development of Uromyces appendiculatus var. appendiculatus in Phaseolus vulgaris

Abstract

The morphology of intercellular and intracellular hyphae derived from basidiospores of Uromyces appendiculatus var. appendiculatus is described. Light and electron microscopic observations of the bean rust fungus were made on susceptible leaves of Phaseolus vulgaris from 3 to 10 days after inoculation. Following egress from invaded epidermal and palisade parenchyma cells, the fungus grew rapidly and developed extensive intercellular mycelium. An amorphous to fibrillar extracellular matrix was deposited between fungal and host cell walls. Intercellular hyphae grew closely appressed to the mesophyll cells and penetrated them to form intracellular hyphae from either a terminal or nonterminal mother cell. Intracellular hyphae were fingerlike, sometimes septate, and generally remained terminal in the invaded mesophyll cell. Occasionally the fungus exited the cell to become an intercellular hypha or an intracellular hypha in an adjacent host cell. The plant rarely exhibited a resistantlike reaction at sites of penetration into mesophyll cells.