Abstract:
In the mid-2000s an outbreak of bacterial blight and dieback caused by Xanthomonas
vasicola pv. vasculorum was observed on a single Eucalyptus grandis clone in
KwaZulu-Natal. It was suggested that this outbreak was as a result of a host jump from
sugarcane. Therefore, the purpose of this dissertation is to determine the host range
of X. vasicola strains and to identify the genetic determinants which may have played
a role in this pathogen’s ability to jump to a new host. This dissertation will be
presented in three independent chapters.
Chapter 1 will review previous literature on the changes that take place in a bacterial
genome leading to its adaptation to a changing environment. The chapter will include
sections on the modifications of existing genes by mutations, gene duplications and
gene rearrangements, acquisition of new genes by horizontal gene transfer, and the
loss of genes as pathogens become specialised to their hosts.
In chapter 2, the host range of X. vasicola strains isolated from different hosts will be
tested. Host’s include the monocotyledonous plant species banana, maize, sorghum,
sugarcane and the dicotyledonous plant species Eucalyptus grandis. The significance
of the differences observed between the number of infected plants and the severity of
the disease symptoms will be determined.
In chapter 3, the differences between the genomes of five Xvv isolated from E. grandis
and X. vasicola isolated from other hosts will be determined. The genomes of five Xvv
strains from Eucalyptus were sequenced on the Illumina HiSeq 2500 platform. The
chromosomes and plasmids were assembled and annotated, and the genomes were
compared to those of other X. vasicola strains isolated from different hosts. These
genome differences may have played a role in their adaptation to a new host.
