Ultrastructure of susceptible, resistant, and immune reactions of tomato to races of Cladosporium fulvum

Abstract

Ultrastructural examination of the Cladosporium fulvum Cooke – tomato combination was carried out to reveal the nature of the host–parasite interaction. The tomato varieties V-121 (Cf3) and Vinequeen (Cf2, Cf4), inoculated with race 1, served as the resistant hosts. Vinequeen, inoculated with race 12, was used as the susceptible host.Relatively few ultrastructural changes were observed in the susceptible host until sporulation was extensive. In the resistant V-121 host, cytological changes occurred within the lesion area just before aerial mycelia formation (about day 8) and included cytoplasmic disorganization, increased electron density of cytoplasm, limited callose formation, and the association of extracellular material with the cell walls. In the susceptible host, the mycelium was rich in polysaccharide and lipid-like substances, in contrast with the mycelium in V-121 lesions, which was highly vacuolated and had an additional electron-dense layer on the cell wall surface. The reaction of the highly resistant (immune) Vinequeen to race 1 had occurred by day 6 and was characterized by massive callose deposition. Cells within the infection court often had highly vacuolated cytoplasm or were completely decompartmentalized. The hyphae in most instances were probably dead since they either appeared plasmolyzed or were filled with an amorphous material.