Date of Award

1986

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

Calli derived from 'Tangi' (susceptible) and MSUS 42 and LA 8318 (resistant) exhibited differential responses when inoculated with Colletotrichum fragariae, isolate CF1. The best differential in terms of growth and multiplication of the fungus was observed at 15(DEGREES)C and this differential decreased with increasing incubation temperature and time. Level of benzyladenine in the medium did not affect disease expression. Susceptible tissues exhibited extreme sensitivity, characterized by intense discoloration and cessation of growth, when subcultured onto a medium containing the culture filtrate of C. fragariae while the resistant tissues were affected less. The efficacy of the culture filtrate was not affected by autoclaving. The culture filtrate also induced more electrolyte leakage from the susceptible tissues than from the resistant tissues. These observations suggest that C. fragariae produces a toxin-like substance in vitro. In vitro disease ratings of eight cultivars/lines were made based on callus response to inoculation with a conidial suspension of the fungus and exposure to culture filtrate of the pathogen. MSUS 42, LA 8318, LA 6261, and 'Apollo' were classified as resistant, 'Earlibelle' as intermediate, and 'Tangi', 'Sunrise', and LA 42311 as susceptible. In vitro screening results correlate well (r = 0.812) with whole plant screening responses.

Pages

87

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