Investigations on the infection of some monocotyledonous plants by Verticillium spp. showed that they were susceptible only to V. dahliae. This was shown by the colonization of the root surfaces and superficial tissues, although V. dahliae was usually present in the microsclerotial form and the viability of these propagules was confirmed. Investigations involving studies of the effect of different crop cover on the soil population of V. dahlias showed that both susceptible and resistant plants increased the number of propagules in the soil. The penetration of wheat roots by V. dahlias in culture was studied. Here light and electron microscopy were used to study the infection process. The light microscope showed that the plant was able to resist vascular penetration by the fungus. This resistance to penetration appeared to be due to the formation of barriers such as lignification and lignituber formation.in the cell walls. Varying the pH of the medium and growing the seedlings and fungus at different temperatures had no apparent effect on the extent of penetration. Resistance appeared to be a feature of living cells presenting an active response to infection. A comparison of spore germination on susceptible and resistant roots indicated that there was no inhibitory substance/s produced by the resistant plant. Transmission electron microscopy presented convinving evidence that resistance to penetration was due to the formation of deposits on the innerface of host cell walls (referred to as lignitubers). In electron micrographs these lignitubers appeared as membranous pads composed of alternating electron dense and electron lucent material. They were apparently formed by the host cytoplasm as a result of the aggregation and fusion of protoplasmic vesicles with the host plasmalemma. The host cell wall produced "covering material" which appeared to be a modification of the wall. This material formed around any hyphae that were in contact with the wall and possibly served to suppress infection. Histochemical tests of the "covering material" showed that it was composed of cellulose. The penetration of wheat root by a virulent fungus, viz. Fusarium culmorum was also studied by light and electron microscopy and it was found that this fungus penetrated the wheat root with little or no host reaction.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:637988 |
| Date | January 1978 |
| Creators | Malik, N. K. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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