The host-pathogen interaction of lucerne (Medicago sativa L.) with isolates of the vascular wilt fungus, Verticillium, was investigated. Pathogenicity trials showed that only isolates of Verticillium from lucerne were pathogenic to this host. Lucerne cultivars resistant to European isolates of the pathogen were not resistant to the more virulent American isolates of the fungus. The production of phytoalexins by the host in response to isolates of Verticillium was investigated. The specialised pathogenicity of the lucerne isolates was correlated with their induction of low levels of phytoalexins in the host while non-pathogenic isolates of Verticillium induced high phytoalexin levels in lucerne. Several factors e.g. incubation period and age of leaf material affected the levels of phytoalexin which accumulate in the diffusates of lucerne leaflets. An investigation of the induction mechanism for phytoalexins in lucerne revealed that culture filtrates and spore free filtrates did not provide sufficient stimulus for phytoalexin induction. Of treatments used, only viable Verticillium spores and copper chloride solutions induced phytoalexin production. Penetration of the epidermal layer of lucerne leaves by a non-pathogenic isolate of Verticillium resulted in the rapid necrosis of epidermal cells and an associated accumulation of phytoalexins in both leaf diffusate and leaf tissue. It is suggested that the reaction of the host to the non-pathogenic isolate represents a hypersensitive response i.e. rapid cell necrosis with associated accumulation of phytoalexins. In contrast, penetration by the pathogen took several days. Although phytoalexins were eventually produced, their production did not limit the growth of the pathogen and the whole leaf became necrotic and ramified with mycelium.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:636980 |
| Date | January 1980 |
| Creators | Flood, J. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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