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Title: Comparative behaviour of mycoparasitic Pythium species
Author: Jones, Elisabeth Eirian
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1994
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The nutrition and physiology of the mycoparasites Pythium oligandrum, P. mycoparasiticum and P. acanthophoron differed from that of plant pathogenic Pythium spp., but with minor variations between strains and species of the mycoparasites. P. oligandrum, P. mycoparasiticum and P. acanthophoron did not use inorganic nitrogen. P. oligandrum and P. mycoparasiticum required exogenous thiamine, whereas P. acanthophoron was self-sufficient for thiamine. The mycoparasites grew on mannitol as a carbon source in the presence of cholesterol, calcium or both, but the effects of calcium and cholesterol differed between the mycoparasites, and isolates of P. mycoparasiticum were intolerant of ethanol, used as the solvent for cholesterol. P. oligandrum. P. acanthophoron and P. mycoparasiticum, tested as single strains, showed different growth responses to ergosterol, cholesterol and β - sitosterol. These mycoparasites were less tolerant of elevated NaC1 concentrations than were P. ultimum and P. aphanidermatum, and grew much better in complex undefined media than in defined media. Of various media tested, 3% molasses gave maximum oospore production, Oospores of P. oligandrum and P. acanthophoron showed maximum 17 - 19% germination after 18 h incubation on agar at 25oC, when oospores were harvested from 5-week cultures on molasses medium. The apparent viability of oospores, determined by tetrazolium bromide stain, was 75% and 90% respectively, contrasting with the low germinability. Oospores required an ageing period of 35 days, which was nutrient-independent, before they showed maximum germination. Storage of oospores in air-dried culture biomass reduced their germinability. Of many treatments used, the maximum percentage germination (c.30%) was obtained after treatment with 0.001% potassium permanganate. However, culture-produced oospores of P. mycoparasiticum consistently failed to germinate and seemed to be non-viable when stained with tetrazolium bromide. The low germinability of oospores of mycoparasitic Pythium spp. in general, especially after dry storage, could be a major limitation to their use as biocontrol agents of plant pathogens.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available