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Title: Studies on the elicitation of lucerne (Medicago sativa L.) phytoalexins by Verticillum spp.
Author: Onuorah, O. M. O.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1982
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The production of phytoalexins by the lucerne cultivars Dupuits (susceptible to Verticillium wilt) and Maris Kabul (resistant to Verticillium wilt) in response to substances (= elicitors) produced by pathogenic and non-pathogenic isolates of Verticillium albo-atrum was investigated. The elicitors are produced in culture filtrates from the log-phase and past log-phase stage of growth. They are also extractable from the mycelial walls. Certain similarities in the biological and chemical properties of the culture filtrate and cell wall elicitors suggest that the culture filtrate elicitor is derived from the mycelial wall. The elicitors were purified by gel-filtration and ion exchange chromatography. They were found to be thermostable and non-dialysable and proved sensitive to sodium periodate, protease and sodium hydroxide treatment which suggests that they are glycoproteins. Both elicitors contain mainly glucose, mannose, galacose and protein. The protein component is rich in aspartic + acid, glutamic acid, alanine, proline, glycine, threoaine and serine. Molecular weight of the culture filtrate elicitor was found to be ca. 4.5 x 104. When the culture filtrates from both pathogenic and nonpathogenic isolates were allowed to permeate cut shoots via the transpiration stream of either lucerne cultivar, phytoalexins were produced in the leaves but not in the stems. No difference in the reaction of the cultivars to this elicitor from either isolate was apparent, i.e. there was no evidence of strain or cultivar specific reaction. Specificity as reflected in the level of phytoalexin production is only exhibited when drops of spore suspension of the respective isolates are placed on the surface of excised leaves. Although the culture filtrate and cell wall elicitors had many similarities, some evidence for a differential activity in phytoalexin production in the two cultivars was obtained.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available