Abstract
M.Sc.
A variety of micro-organisms are constantly exploiting plants. Barley is no exception and
various pathogens attack it. This interaction between the plant and the pathogen can be
divided into two groups. A compatible interaction occurs when the plant shows
susceptibility to the pathogen. An incompatible interaction occurs when the plant shows
resistance to the pathogen. This incompatible interaction is usually associated with
necrotic lesions at the infected area. The aim of this project was to study the interaction
between Hordeum vulgare (barley) and Fusarium graminearum (causal agent of head
blight / scab). Further objectives were to look at the expression of defence genes in the
cultivar Puma 15 when infected with F. graminearum. Juvenile plants were used in this
study and infected at the third leaf stage. Suppression subtractive hybridisation (SSH)
was performed on inoculated and uninoculated plants to enrich for differentially
transcribed genes. The resulting transcript derived fragments (TDF) were cloned and
sequenced. Several stress related (biotic or abiotic) genes were identified that included
putative selenium-binding proteins (SSH10), glutamine-dependent asparagine
synthetase 1 (SSH11) and hypothetical proteins. Upon inspection of the homology at
nucleotide level of one of the hypothetical proteins (SSH16), it became evident that it
was from the 26S ribosomal gene. A selection of the identified genes was further
evaluated to the role that they play during this specific interaction by Northern blot
analyses. Northern blot analysis of the putative selenium binding homologue (SSH10)
showed low levels of induced gene expression in the inoculated plants as compared to
the control at 24 hpi. For the asparagine synthetase homologue (SSH11) there was a
significant up-regulation in the inoculated sample at 24 hpi. From the results obtained in
this study it was found that there are certain defence related, stress related, and
unknown genes that are expressed during infection of the barley cultivar Puma15 with
F. graminearum. A correlation could be made between the results presented here and
literature on F. graminearum infection studies. When F. graminearum infects the host it
will respond to that infection between 24 hpi and 72 hpi. This response includes the
expression of defence genes and other antifungal mechanisms. The results from this
study complements previous studies and will in future aid in the understanding of barley
responses after infection by necrotrophic pathogens.