Molecular characterization of Fusarium isolates from Ethiopia

Abstract

The taxonomy of Fusarium species has been controversial. The controversy surrounding the morphology-based classification, as well as the limitations and advantages of the various tools used to circumvent this problem are discussed as an introduction to the research presented in this thesis. Emphasis in this case was on the F. oxysporum species complex. The body of the research focuses on Fusarium species in Ethiopian agriculture about which little has been published. Results from this study suggest that F. oxysporum and F. solani are the two species most commonly isolated from agricultural soils and plant tissues from Ethiopia. The Ethiopian F. solani isolates were further characterized using AFLPs which showed that these isolates group into two separate clusters. Additional characterization using EF-1á sequence analyses showed that all these isolates belong to one of the three clades previously designated for the F. solani-Nectria haematococca species complex. Nine SSR markers were developed for studying the F. oxysporum complex. These markers are highly polymorphic and should be useful for many different population genetic studies of the F. oxysporum species complex. Ethiopian F. oxysporum isolates, and F. oxysporum isolates obtained from other fungal collections, were characterized using AFLPs, SSRs and DNA sequence analyses. These studies resolved the isolates into three concordant groups that corresponded to the three clades of F. oxysporum previously designated for this species complex. Most of the Ethiopian isolates grouped in one of these three clades. This and the high degree of AFLP- and SSR-based genetic similarity observed among the Ethiopian isolates suggested that these isolates are largely clonal. In addition, a PCR-based diagnostic was developed to allow for the accurate differentiation between F. oxysporum and F. redolens which has proved to be difficult using morphological characters. The studies presented in this thesis contribute to a better understanding of Fusarium species commonly found in Ethiopia. Clearly, there is much that will still need to be done. The research presented in this thesis establishes a foundation for other studies and also provides a stimulus for further studies of these important fungi in Ethiopia. Copyright 2006, 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. Please cite as follows: Bogale, MA 2006, Molecular characterization of Fusarium isolates from Ethiopia, PhD thesis, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-11072006-172206 / > D87/ag