The reported pathogenicity of V. albo-atrum and V. dahliae to potatoes and antirrhinums was confirmed. Pectic enzyme secretion by V. albo-atrum and V. dahliae was studied in vitro, in cultures grown on pectin, sodium polypectate, and extract cell wall material from both potato and antirrhinum respectively. The enzymes were produced sequentially over two to twelve days. Endopolygalacturonase (endo PG) was the first formed enzyme in this sequence, followed by exopolygalacturonase (exo PG), and pectin transeliminase (PTE). V. alboatrum generally exhibited higher pectic enzyme activity than V. dahliae. The production of these enzymes was subjected to varying degrees of induction and repression when a high or low concentration of D-galacturonic acid or D-glucose was present in the medium. Properties of enzymes were investigated in terms of pH optima, fungal growth, maceration and cell death of potato tissue, mechanism of substrate degradation, purification and molecular weight determination. Studies on plants infected by V. albo-atrum and V. dahliae suggested an involvement of endo PG in the production of wilt symptoms. These were: a) detection of endo PG but not exo PG or PTE in infected plants and in infected cuttings; b) reproduction of symptoms in potato and antirrhinum cuttings with partially purified endo PG. An extract from the cell walls of both potatoes and antirrhinums was found to inhibit the endo PG secreted by both V. alboatrum and V. dahliae. There was no corresponding inhibition of the exo PG or MI enzymes. The significance of the formation of "blisters" in vascular vessels in response to infection by V. albo-atrum and V. dahliae is discussed in relation to the vascular discolouration. The formation of thin outgrowths from hyphae to vessel walls in the xylem of potato stems and the occurrence of "blister" are highly related. A solid medium on which the production of extracellular pectic enzymes by several isolates of V. albo-atrum and V dahliae, as well as V. tricorpus, V. nubilum and V. nigrescens can be detected is described.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:636000 |
| Date | January 1983 |
| Creators | Bahkali, H. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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