Differences in morphology may predispose certain cultivars to disease by influencing the duration free water remains on the head and the availability of sites for infection. Head shape (doming), head size, bud number, bud prominence and stomatal number were assessed. Whilst these factors differed significantly between cultivars, two sets of factors correlated positively at a significant level: head size and disease susceptibility, and head doming and disease resistance. Biosurfactants, produced by pathogenic bacterial strains, have been implicated in the development of head rot on unwounded heads, by aiding bacterial establishment and spread. Their role in disease, as virulence or pathogenicity factors, was assessed using a mutant approach. Initially, five biosurfactant detection tests were evaluated to allow the mutants produced to be tested for loss of production. The most suitable proved to be monitoring changes in the surface tension of a water droplet following the addition of bacterial cells removed from a colony. Thirty-five mutants, defective in biosurfactant production (surf <SUP>-</SUP>), were produced by Tn5 mutagenesis. Because some surf<SUP> -</SUP> mutants were unaffected in their ability to cause disease, it was concluded that biosurfactant production in <I>P. fluorescens</I> is neither a virulence nor a pathogenicity factor. Biosurfactants are probably produced, in this bacterium, to assist initial establishment and colonisation of the plant surface. Further work is required to elucidate the nature of the mutated genes to define the precise role of biosurfactants in the host/pathogen interaction.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:649115 |
| Date | January 1999 |
| Creators | Darling, Denise |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/27862 |
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