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Title: Transmission studies on the potato pathogens Fusarium solani var. Coeruleum and Fusarium sulphureum
Author: Jeffries, Colin John
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1979
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A new selective medium containing pentachloronitrobenzene and 2-aminobutane - the PAB medium - was developed for use with the soil-dilution plate method for the enumeration of fungal propagules of F. solani var. coeruleum and F. sulphureum in field soil. These fungi cause a dry rotting of potatoes in storage. The efficiency of the PAB medium in the measurement of levels of soil contamination was compared with that of other methods. Also described is the PM70 medium, suitable for the isolation of a number of pathogens, including P. exigua. var. foveata from diseased tuber tissue. The incidence of dry rot after grading was related logarithmically to the number of F. solani var. coeruleum propagules in progeny tubersphere soil. Highest levels of progeny tuber contamination with F. solani var. coeruleum were associated with the planting of infected seed. Planting of contaminated seed sometimes gave high levels of transmission, possibly because dry rot developed after planting. Propagule production by infected seed varied between seasons and may be related to soil temperature. Tuber factors, eg variety and seed size, also influenced propagule production. Of the seed treatments tested, only thiabendazole reduced consistently the transmission of F. solani var. coeruleum. Levels of soil contamination increased during the growing season but removal of the seed tuber prevented further increase. Highest numbers of propagules were in a 5cm diam. zone of soil surrounding the seed and spread of propagules was mainly lateral and downwards forming a decreasing gradient of inoculum with increasing distance from the seed tuber. Propagule distribution on progeny tubers followed the same pattern but harvesting by elevator digger disturbed the soil inoculum, making all progeny tubers highly contaminated. F. solani var. coeruleum survived a 6 year rotation in field soil and this soil-borne inoculum is possibly important in the re-contamination of clean seed stocks. Most varieties, of those tested, were resistant to infection by F. solani var. coeruleum in November but susceptible by February. Tubers were more susceptible if incubated initially at 40°C rather than at 15°C. Transmission of F. solani var. coeruleum was compared with that of F. sulphureum. Propagules of F. solani var. coeruleum were produced in cavities in the tuber and in pustules on the tuber surface but F. sulphureum showed little surface sporulation. Thus thiabendazole, which inhibits surface sporulation, was inconsistent in reducing transmission of F. sulphureum. Moreover, F. sulphureum sporulated on stems growing from infected seed tubers in the field. F. sulphureum infected seed usually produced less inoculum than did F. solani var. coeruleum but in one season the reverse was true and was possibly related to high soil temperatures. F. sulphureum does not appear to survive in field soil as well as F. solani var. coeruleum. Although F. sulphureum seems less well adapted than F. solani var. coeruleum for propagule transmission, none of the varieties tested was resistant to infection by F. sulphureum.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available