DNA polymorphisms as genetic markers in cereal rust fungi
Author(s)
Smith, Joanne Marie
Type
Thesis
Abstract
The obligate biotroph Puccinia hordei is the causal agent of brown rust of barley. Knowledge of the population genetics of P.hordei and other cereal rust fungi has been limited by a lack of easily scored, heritable markers. Worldwide surveys show that rust pathogen populations are often polymorphic for genes determining virulence. In the work described, variation within a P.hordei population was studied using virulence markers and molecular markers. Virulence markers revealed variation in the virulence combinations of isolates of a small local population, and suggested that the population studied was dominated by one race. The occurrence of restriction fragment length polymorphisms (RFLPs) and random amplified polymorphic DNA markers (RAPDs) was investigated in the genomes of 22 P.hordei isolates from around the UK, and a smaller number of global P.hordei and P.striiformis isolates. Fungal-specific probes were hybridised to DNA extracted from rust-infected barley, facilitating the analysis of these fungi. DNA probes detected polymorphisms between P.hordei and P.striiformis f.sp. hordei, revealing considerable genetic variation between these two species. Random DNA probes from a library of cloned restriction fragments of P.hordei genomic DNA did not detect any polymorphisms among the P.hordei isolates. Polymerase chain reaction parameters were established for the amplification of stable, reproducible RAPD markers to analyse cereal rust populations. RAPD markers distinguished P.hordei and P.striiformis f.sp. hordei and revealed a small number of polymorphisms between global P.hordei isolates. The intergenic spacer (IGS) region of P.hordei rDNA was analysed, as rDNA spacers are often polymorphic within and between species. A rDNA IGS region was amplified from six diverse P.hordei isolates using the polymerase chain reaction and sequenced to assess genetic variation between these isolates. The IGS region contained short tandemly repeating nucleotide sequences and several homopolymeric tracts of A and T residues. The sequence was highly conserved among the P.hordei isolates analysed.
Version
Open Access
Date Awarded
1992
Advisor
Buck, Professor K.W.
Newton, Dr. A.C.
Sponsor
SERC Studentship
Scottish Crop Research Institute.
Publisher Department
Department of Life Sciences
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)