Phytophthora erythroseptica, the causal agent of pink rot of potato was found to produce more sporangia with non-sterile soil extract than with Petri's solution. Centrifugation of the growth medium above 3,000 £ reduced the number of sporangia formed, whilst low intensity light at all wavelengths except ultraviolet light (300-400 nm) was stimulatory to sporangial production. Zoospores of the fungus were shown to be attracted to low concentrations of ethanol under laboratory conditions though this was not observed in the field. Germination of oospores of P. erythroseptica was variable and differences between naturally produced and culture-produced oospores were recorded. Activation, a prerequisite for germination was increased by incubation in blue light and by exposure to low temperature, though germination was highest at 20°C under white light. Germination was not stimulated by heat treatment, addition of various chemicals, the carbon source of the media or root exudates. However, continuous washing of oospores with water substantially increased germination particularly of oospores isolated from plant " tissue. Treatment of oospores with enzymes increased germination, snail gut enzyme being most stimulatory. Oospores recovered after passage through the. gut of the greyffield. slug, Doraceros reticulatus, were able to germinate immediately., A relationship between slug damage and pink rot was noted though cause and effect could not be determined. Oospores were shown to be parasitised by a large range of microorganisms in soil, with Chytridiomycetes most numerous in waterlogged soils and Hyphomycetes most numerous in drier soil. Levels of up to 36% parasitism were recorded in some soils, and the implications of this on the population of P. erythroseptica propagules is discussed. The level of inorganic nitrogen did not affect disease incidence, though water availability was shown to be necessary for disease development. Control of pink rot was achieved using the new group of acylalanine fungicides, with Metalaxyl proving most effective at 5.0 kg ai/h. The implications for future control of the disease are discussed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:505869 |
| Date | January 1981 |
| Creators | Wynn, A. R. |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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