Hordeum bulbosum L. (bulbous barley grass) is an important genetic resource for barley (Hordeum vulgare L.) improvement. As the sole member of the secondary genepool of Hordeum; H. bulbosum represents a relatively untouched source of genetic diversity which can provide novel allelic variation for traits critical to the future of barley breeding. In order to access this resource efficiently, a complete set of molecular marker resources is necessary to assist the introgression of chromatin from H. bulbosum into a barley genetic background.
For breeders to access traits from H. bulbosum for barley improvement, recombinant lines need to be developed to transfer regions of the H. bulbosum genome into a barley background for trait identification and for incorporation into elite barley breeding programs.
The chromosomal location of H. bulbosum introgressions in thirty eight unique recombinant lines was performed using RFLP analysis using mostly distal probes from barley genetic linkage maps However, this analysis was labour intensive, restrictive and prone to inconsistencies due to low intensity signals and complex banding in H. bulbosum.
Due to the low level of interspecific recombination detected between the two species, a retrotransposon-like marker, pSc119.1, was developed which could be used to quickly screen progeny from an interspecific cross to determine which lines possessed introgressions of chromatin from H. bulbosum.
After initial screening, putative recombinants were further characterised using co-dominant single locus PCR markers from throughout the genome. A focus was made on using the EST resources of barley and wheat, combined with the rice genome to create intron-spanning markers. Subsequent allele-sequencing revealed high frequencies of species-diagnostic single nucleotide polymorphisms (SNPs) in the intron regions of these markers, coupled with relatively low frequencies of species-diagnostic SNPs in the flanking exon regions. Overall, interspecific SNP frequencies were not significantly higher in intron-spanning markers than those consisting of exon-only sequence. However, species-diagnostic indels were more frequently discovered within intron sequence providing additional polymorphism.
Recombinant lines with phenotypes that differed from the barley parent allowed those traits to be assigned to particular chromosomal regions. These characterised recombinant lines will provide a resource for barley breeders to identify novel traits for barley improvement and allow identification of new alleles in different chromosomal locations for current traits, allowing greater flexibility for cultivar construction.
A targeted backcross population of the recombinant line 38P18/8/1/10 (possessing leaf rust resistance derived from H. bulbosum) was created. The introgressed region was saturated for PCR markers using a variety of marker types and techniques (AFLP, cDNA-AFLP). Two lines were subsequently identified with introgressions of reduced size relative to the parental recombinant line, both of which have retained the leaf rust resistance trait. The leaf rust resistance was finally linked to two co-dominant EST-based markers located on chromosome 2HL by using these two lines and the direct screening of progeny from interspecific hybrids possessing introgression junctions in the region of interest.
In general, recombinant material between barley and H. bulbosum suffers from certation effects which cause distorted segregation that favours heterozygous and homozygous barley genotypes. Two unique lines have been identified during this research that possess gametocidal-type loci that result in the absolute retention of H. bulbosum chromatin with the termination of gametes lacking the introgression (barley genotype only).
| Identifer | oai:union.ndltd.org:ADTP/217820 |
| Date | January 2008 |
| Creators | Johnston, Paul Andrew, n/a |
| Publisher | University of Otago. Department of Biochemistry |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://policy01.otago.ac.nz/policies/FMPro?-db=policies.fm&-format=viewpolicy.html&-lay=viewpolicy&-sortfield=Title&Type=Academic&-recid=33025&-find), Copyright Paul Andrew Johnston |
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