Resistance to Walnut Anthracnose Development in Juvenile Leaves of Black Walnut Seedlings
Cline, Steven Donald
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Permalink
https://hdl.handle.net/2142/70584
Description
Title
Resistance to Walnut Anthracnose Development in Juvenile Leaves of Black Walnut Seedlings
Author(s)
Cline, Steven Donald
Issue Date
1982
Department of Study
Plant Pathology
Discipline
Plant Pathology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Plant Pathology
Abstract
Walnut anthracnose is the most serious foliar disease of black walnut causing premature defoliation and reduced growth. Early studies failed to identify functionally resistant cultivars of balck walnut to this disease. From previous artificial inoculation studies on greenhouse-grown seedlings, juvenile leaves were observed to be less infected than mature leaves. The mechanism(s) of juvenile-leaf resistance in black walnut seedlings was investigated through histopathological, artificial inoculation, and biochemical studies.
Forty-eight hours after inoculation, conidial penetration via appressoria was direct through cell walls of the leaf epidermis. Germ tube formation was inversely related to the success of penetration. Host-formed papillae were commonly associated with attempted penetration sites and prevented any further fungal development. Papilla formation was similar and of equal frequency in juvenile and mature leaves. Colonization of single cells, cell to cell spread, and microscopic necrosis was observed between 72 and 168 hours after inoculation. Macroscopic lesions were observed at 240 hours. Acervuli were initiated at 240 hours and a mature fruiting body was formed shortly thereafter on mature leaves.
From artificial inoculations, the abaxial surface was determined to be about 40 times more susceptible than the adaxial surface. Reduced infection of the adaxially inoculated surface was associated with a tendency for conidia to produce germ tubes without appressoria. Juvenile leaves were not found to be less susceptible to the anthracnose fungus provided that leaf expansion between inoculation and symptom development was considered. Lesion size and acervulus production was correlated with leaf age. Smaller lesions and fewer acervuli were found on progressively younger leaves.
In general, pathogens of black walnut were more tolerant of juglone when compared with nonpathogens as measured by their growth in augmented media. Hydrojuglone glucoside stimulated the growth of the anthracnose fungus in vitro.
Juglone and hydrojuglone glucoside concentrations were higher in juvenile leaves. In anthracnose-infected leaves, hydrojuglone glucoside levels were higher while juglone levels were lower compared to noninfected leaves.
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