Molecular and Biochemical Characterisation of Armillaria

Abstract

Armillaria spp. are important root pathogens that cause considerable plant mortality throughout the world. The nomeclatural and taxonomic placement of the genus has been intensely debated for a long time. Early identification relied exclusively on mating tests and morphological similarities. The introduction of DNA and protein based methods has greatly increased the understanding of the phylogeny of Armillaria species. The literature surrounding Armillaria, Armillaria root disease, characters that are distinct to Armillaria, means of disease spread and techniques that have been used to identify Armillaria spp. are considered in this thesis. The controversy surrounding the proper genus name and which species should be included in the genus is also discussed. In this study a collection of isolates obtained from Zimbabwean plantations are characterized. IGS-1 sequence data and AFLP data grouped these isolates into four groups while RFLP data separated them into five groups. One group has been tentatively identified as A. fuscipes whilst the remaining ones have not been described due to scarcity of basidiocarps in the field. A broad selection of Armillaria spp. representing most of the known species were characterized using EF 1-<font face="symbol">a</font> DNA sequences and pectic enzymes. Isolates from the Southern Hemisphere were clearly separate from those originating in the Northern Hemisphere. Within these two large clades, isolates formed subclades indicating their relatedness. Both techniques confirm relationships between species reported previously using other techniques. This is however the first study that presents the molecular phylogeny of Armillaria based on a single copy protein coding gene. The identification techniques used in this study were valuable for species characterisation. Absence of fruiting bodies however, made morphological classification impossible. The results of this thesis should be useful in the process of developing future disease management strategies for Armillaria root rot in Zimbabwe.