In glasshouse and laboratory conditions, death of root cortices of cereal and tomato plants was followed by nuclear and cytoplasmic staining methods. Various treatments were applied to whole plants or sterile root pieces on agar, to study factors that influence root tissue senescence and its relationship to invasion by the parasitic fungi <i>Microdochium bolleyi, Pyrenochaeta lycopersici</i> and <i>Gaeumannomyces graminis</i> var. <i>tritici (Ggt)</i>. Other experiments involved growth and sporulation of <i>M.bolleyi</i> in culture, and the ability of this fungus to spread on roots by spores produced on seeds or roots, to facilitate development of <i>M.bolleyi</i> as a seed-applied biocontrol agent of plant pathogens. Nuclear staining with acridine orange was satisfactory for assessing root cell viability in cereals but not in tomato, for which neutral red/plasmolysis was used; no other cytochemical method was suitable for routine work with either plant. Sterile detached root pieces of wheat and tomato senesced rapidly on media without sucrose, but tomato root cells remained alive on media of low sucrose concentration (0.1&37), whereas wheat root cortical death (RCD) was delayed but not inhibited by even high sucrose levels. RCD was also delayed by removal of the shoot, root tip or seed from sterile wheat seedlings; supply of sucrose or minerals to only part of a root piece did not affect the pattern of RCD. Indolylacetic acid, Ag<SUP>+</SUP> or Co<SUP>2+</SUP> delayed RCD in wheat root pieces on agar, but other growth regulators accelerated RCD. The results suggest that RCD in cereals is programmed and internally regulated, being only slightly modified by external factors. <i>M.bolleyi</i> invaded senescing cereal root cortices mainly intercellularly. It accelerated RCD of detached roots but had little effect on attached roots; it invaded tomato roots only poorly. <i>P. lycopersici</i> invaded cereal and tomato roots mainly intracellularly and killed the tissues, indicative of a different growth habit. Wheat, barley, oats and rye showed different rates of RCD in root pieces on agar, and oats had a different pattern of RCD from that in other cereals. <i>Ggt</i> killed roots of all four cereals, attached and detached from seedlings, but it penetrated poorly into oat roots even when their cells died. An attempt was made to relate these events to patterns of induced lignification in root cells.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:653687 |
| Date | January 1990 |
| Creators | Lascaris, Dimitrios |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/11031 |
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