Fusarium is a soilborne fungus which can live in soil for long periods of time. It is known to
cause wilt, root rot and crown rot diseases in a diverse group of crop plants. Of all the
diseases caused by Fusarium the most important are the vascular wilts. Pathogens that
cause wilting usually enter their host plant through young roots and then grow into and up
the water-conducting vessels of the root and stem. The vessels become blocked and water
supply to the leaves is limited. This results in the potato plant being weak resulting in
yellowing of leaves, browning of stems and production of smaller tubers. Fusarium is diverse
and widely distributed and can be isolated from agricultural soils and plant material. The
study was done to determine the occurrence of this pathogen in the South African potato
industry. Samples of plant material showing wilt symptoms were collected from nine potato
production regions. Fungal isolations were made from tubers using a Fusarium selective
medium, i.e Peptone PCNB Agar. The isolates were examined morphologically and those
resembling Fusarium were further identified using molecular techniques. DNA sequence
analysis of the translation elongation factor 1-α gene was done on the isolates. DNA-based
techniques have increasingly become the tool of choice for understanding the genetic
diversity and phylogeny of Fusarium species. The pathogenicity of the isolates from all the
regions was also investigated on potato cultivar Caren. The DNA results confirmed Fusarium
as the pathogen causing Fusarium wilt on potatoes. Two species of Fusarium were
identified; namely F. oxysporum and F. solani. F. oxysporum was more prevalent and
occurred in all regions compared to F. solani. F. oxysporum is best known for the plant
pathogenic strain, which cause wilt, root rot and crown rot diseases on a wide variety of
crops, often limiting crop production. It is also known to be phylogenetically diverse. In the pathogenicity test, the isolates were found to be virulent and one was highly virulent
therefore confirming their ability to cause wilting of potatoes. The effect of silicon on
Fusarium wilt of potatoes was investigated in this study to assess its effectiveness in the
control of Fusarium wilt. An in vitro study using potassium silicate was done to determine if
silicon can inhibit the growth of Fusarium at different concentrations. The results showed that
at low concentrations of potassium silicate the growth of Fusarium was not inhibited, while at
a high concentration, there was inhibition. Greenhouse pot trials were conducted to
determine the effect of silicon soil amendments on Fusarium wilt of potatoes, tuber yield and
the production of phenolics in the cell wall of potato peels. The levels of chlorogenic, caffeic
and ferulic acids were also investigated. The following treatments were used: control, silicon
ash (~99% Si), slag (30% Si), fly ash (50% Si) and lime (calcium carbonate) as a pH control.
Treatments were divided into those inoculated with Fusarium and those without Fusarium.
Results showed that for silicon treatments not inoculated with Fusarium, slag had the highest
tuber yield, followed by lime, fly ash and silicon ash when compared to the control. Silicon
treatments inoculated with Fusarium did not improve the yield as the control had the highest
yield and the occurrence Fusarium wilt was not reduced in silicon treatments. In this regard
silicon did not have an effect on Fusarium wilt because symptoms were visible in the silicon
amended treatments. The results for phenolic acid content showed that ferulic acid levels
were too low for analysis; for chlorogenic acid, concentrations were generally lower in the
silicon treatments than in the treatments without silicon; and caffeic acid levels were higher
in silicon treatments than treatments without silicon, as a result of increased production of as
defence mechanism against invading pathogens. However, this is the first study on the effect
of silicon on Fusarium wilt of potatoes and its influence on the production of phenolics.
Further research is required to understand the role of silicon in potato pathosystems. / Dissertation (MSc)--University of Pretoria, 2013. / gm2014 / Microbiology and Plant Pathology / unrestricted
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:up/oai:repository.up.ac.za:2263/33188 |
| Date | January 2013 |
| Creators | Nxumalo, Nokukhanya Nokuphila |
| Contributors | Van der Waals, Jacquie E. (Jacqueline Elise), nxumalonn@hotmail.com, Coutinho, Teresa A. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Rights | © 2013 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
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