The aims of the project were to define the signals provided by the cereal host which induce cereal rusts to form appressoria over stomata, and to analyse the mechanism by which these signals are transduced. Using polystyrene replicas of microfabricated silicon wafers to provide precisely defined topographies, appressoria were induced in all the cereal rusts analysed (<I>Puccinia graminis</I> f. sp. <I>tritici, P. graminis </I>f. sp. <I>avenae, P. graminis </I>f. sp. <I>secalis, P. recondita</I> f. sp. <I>tritici, P. coronata </I>f. sp. <I>avenae </I>and <I>P. hordei</I>) by topographies with closely spaced (1.5 μm) ridges. Ridges of different heights (between 0.116 μm and 2.4 μm) were tested. The patterns of response to different ridge heights was not correlated to host nor rust species. Only one rust, <I>P. graminis</I> f. sp. <I>secalis</I>, formed significant numbers of appressoria (up to 62%) on ridges spaced 50 μm apart (= single ridges). The formation of appressoria on host leaves was found to be very efficient, 92-95% of germlings encountering a stoma formed an appressorium over the stoma. On polystyrene host leaf replicas, however, the efficiency was much less, and varied significantly between rusts (4%-63%). Again, the variation was not correlated to host or rust species. The implication was that while topographical signals alone are sufficient to induce appressoria <I>in vitro</I>, topography of the host alone was not sufficient to explain the high efficiency of appressorium induction seen <I>in vivo</I>. It was shown for <I>P. graminis </I>f.sp<I>. tritici</I> that the volatile compounds <I>trans</I>-2-hexen-1-ol and <I>cis</I>-3-hexen-1-ol, produced by the host plant as part of the lipoxygenase pathway, induced appressoria in the absence of topographical stimuli. Induction was dose dependent and optimal at 1 mM when applied to the fungus as a solution. Appressoria were also induced when the germlings were exposed to vapour from solutions of <I>trans</I>-2-hexen-1-ol. Induction was over a very narrow range of concentrations (1-2 mM).
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:643345 |
| Date | January 1996 |
| Creators | Collins, Tony J. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/14665 |
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