Abstract:
Avocado (Persea americana Mill.) is an important crop whose cultivation is severely threatened
by Phytophthora cinnamomi Rands. The South African avocado industry makes an important
contribution to the world’s avocado supply, and is one of the world’s largest exporters. If the
current Phytophthora root rot problem is not addressed soon, the losses encountered by the
avocado industry may become so extensive that it results in job losses. The scant information
that is available for P. cinnamomi interaction studies indicate that there is no gene-for-gene
interaction yet described between the pathogen and host. Avocado genomics are not well
understood either and there is not much sequence data available for this basal angiosperm. The
data available comprises of sequence that was generated in marker studies on fruit and
flowering organs. It is now possible to generate large amounts of sequence data using highthroughput
sequencing platforms and identify defence-related genes. The identification of
defence-related genes in a tolerant rootstock will allow us to characterize the avocado-P.
cinnamomi interaction on a molecular level.
The aim of this MSc was to identify defence-related genes in a tolerant rootstock and
characterize their expression in order to understand the avocado-P. cinnamomi interaction.
Chapter 1 provides a comprehensive overview of the advances in molecular work
conducted on avocado thus far. A background of avocado rootstock development is provided
with details of molecular markers developed for use in avocado. Additionally, an introduction is
also given to high-throughput sequencing and its application to non-model crops such as
avocado. Chapter 2 describes the mRNA isolation and EST pyrosequencing of avocado roots.
Gene annotation of metabolic, cell wall associated and stress response genes are provided
along with the characterisation of defence-related genes. Chapter 3 reports of the expression profiling of defence-related genes obtained from
avocado root ESTs. The expression of nine defence-related genes are studied over six time
points in P. cinnamomi infected R0.09 tolerant avocado roots. Chapter 4 provides a general
discussion of the result obtained in this study along with future applications of the sequencing
data produced.
