A population of Arabidopsis thaliana growing locally in a suburb of Zürich called Weiningen was observed to be infected with downy mildew. Plants were collected and the progress of infection was investigated in artificial inoculations in the laboratory. The plants proved to be highly susceptible, and pronounced intercellular mycelial growth, haustoria formation, conidiophore production, and sporulation of the causal organism Peronospora parasitica were all observed. The formation of oogonia, antheridia, and oospores also occurred. In contrast, Arabidopsis strain RLD was resistant to infection and none of the above structures was formed. The fungus was localized very soon after penetration of RLD leaf cells, which responded with a typical hypersensitive reaction. The differential interaction of an isolate of P. parasitica with two strains of Arabidopsis opens up the possibility of cloning resistance determinants from a host that is very amenable to genetic and molecular analysis.
At the beginning of the disease, small, tan-coloured lesions, restricted by leaf veins, can be observed on infected soybean leaves. Lesions enlarge and, 5-8 days after initial infection, rust pustules (uredia, syn. uredinia) become visible. Uredia develop more frequently in lesions on the lower surface of the leaf than on the upper surface. The uredia open with a round ostiole through which uredospores are released.
A population of Arabidopsis thaliana growing locally in a suburb of Zürich called Weiningen was observed to be infected with downy mildew. Plants were collected and the progress of infection was investigated in artificial inoculations in the laboratory. The plants proved to be highly susceptible, and pronounced intercellular mycelial growth, haustoria formation, conidiophore production, and sporulation of the causal organism Peronospora parasitica were all observed. The formation of oogonia, antheridia, and oospores also occurred. In contrast, Arabidopsis strain RLD was resistant to infection and none of the above structures was formed. The fungus was localized very soon after penetration of RLD leaf cells, which responded with a typical hypersensitive reaction. The differential interaction of an isolate of P. parasitica with two strains of Arabidopsis opens up the possibility of cloning resistance determinants from a host that is very amenable to genetic and molecular analysis.
The development of Phakopsora pachyrhizi from infection to uredospore development was studied by light‐ and electron microscopy. Uredospores germinated with a single germ tube, formed appressoria and infected always by direct, cuticular penetration. Penetration started with the formation of an appressorial cone which was continuous with the cell wall of the penetration hypha. The penetration hypha entered the epidermal cell, transversed it and reached the intercellular space of the mesophyll where the first septum was formed separating the penetration hypha from the primary hypha. Spread of the fungus in the tissue was followed in whole‐leaf mounts. The first haustorium was visible between 24 and 48 hours after inoculation. Haustoria were formed in mesophyll and epidermal cells. Occasionally, encapsulations of haustoria were observed. In sections of uredia two cells, obviously the pedicel and the sporogenous cell, were observed below developing uredospores. This indicates that uredosporogenesis in P. pachyrhizi is the same as known from other rust fungi. As in the case of other rusts partial septa and perforate septa were found in the sporogenous tissue. Perforate septa were also observed elsewhere in hyphae of the infected tissue.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.