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Title: A study of the production of ascochitine by Ascochyta fabae and its importance in Ascochyta blight
Author: Beed, Fenton Douglas
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 1993
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Eighteen of nineteen isolates of Ascochyta fabae produced a single phytotoxic compound in culture which was identified by several techniques including proton nmr spectroscopy and electron ionisation mass spectrometry as ascochitine. Yields varied from 7.80 to 86.02 mg 1^-1 but growth of the isolates was similar. Production was maximal at 20 °C on Czapek Dox nutrients supplemented with hot water extracts of the host plant, Vicia faba. High titres were obtained in shake culture but not in still culture unless the surface to volume ratio was large. Two isolates failed to synthesise ascochitine after repeated subculture but production by one of these was restored after passage through V. faba. Passage increased mean production of 16 isolates from 42.79 to 68.13 mg 1^-1. The LD50 concentration of ascochitine for cells from cultivars that were susceptible, tolerant or resistant to the fungus was similar i.e. 3.0±1.2×10^-5 M, 3.8±0.9× 10^-5 M and 2.9±1.1×10^-5 M, respectively. Ascochitine neither affected the germination of seeds nor the growth of mature plants at 5.17×10^-4 M but caused necrosis and wilting of plant cuttings at 2.5×10^-4 M and 5×10^-4 M. There was no association between virulence of 16 isolates of A. fabae for three cultivars of V. faba and the production of ascochitine in vitro, either before or after passage through the host. One isolate produced no ascochitine in vitro and yet was the most virulent for two of three cultivars. The toxin could not be extracted from infected plants. Protocols for the culture of cells of V. faba as callus were developed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available