Genomic regions controlling the expression of adult plant resistance to leaf rust, partial resistance to powdery mildew and grain dormancy in a barley population

Lee Hickey (2012). Genomic regions controlling the expression of adult plant resistance to leaf rust, partial resistance to powdery mildew and grain dormancy in a barley population PhD Thesis, School of Agriculture and Food Sciences, The University of Queensland.

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Author Lee Hickey
Thesis Title Genomic regions controlling the expression of adult plant resistance to leaf rust, partial resistance to powdery mildew and grain dormancy in a barley population
School, Centre or Institute School of Agriculture and Food Sciences
Institution The University of Queensland
Publication date 2012-02
Thesis type PhD Thesis
Total pages 154
Total colour pages 9
Total black and white pages 145
Language eng
Subjects 060412 Quantitative Genetics (incl. Disease and Trait Mapping Genetics)
070305 Crop and Pasture Improvement (Selection and Breeding)
060704 Plant Pathology
Abstract/Summary In Australia, barley (Hordeum vulgare L.) is grown for several end-uses, however, the majority of the grain is produced for the malt export market. Barley cultivars that have recently been released in Australia (e.g. Baudin, Vlamingh, Flagship and Buloke) have improved malt quality, but lack adequate levels of resistance to one or more important foliar pathogens, while Australian cultivars have variable levels of grain dormancy for protection against pre-harvest sprouting (PHS). Additional knowledge of the genetic mechanisms controlling disease resistance (particularly adult plant resistance (APR) or partial resistance) and grain dormancy is required to develop more robust cultivars. In this study, three traits important for adaptation of barley to the northern grain-growing region of Australia (i.e. northern New South Wales and Queensland) were subject to genetic analysis: APR to leaf rust (Puccinia hordei), partial resistance to powdery mildew (Blumeria graminis), and grain dormancy for resistance to PHS. A doubled haploid (DH) barley population derived from a cross between the breeding line ND24260 and cultivar Flagship consisting of 321 lines genotyped with DArT (Diversity Array Technology Pty, Inc.) markers was used to identify genomic regions influencing the expression of these polygenic traits. Phenotype data from multiple environments in Australia and Uruguay, were analysed using both composite interval mapping (CIM) and single-marker genome-wide association analyses to identify novel quantitative trait loci (QTL) for the three traits positioned. QTL were detected on all seven chromosomes, including seven major QTL (i.e. six independent genomic regions) that were critical for expression of the three traits across multiple environments. Two QTL conferring APR in this DH population were detected consistently across four environments; qRphFlag and qRphND (donated by Flagship and ND24260, respectively). qRphFlag was mapped to the short arm of chromosome 5H (5HS), accounting for up to 85% of the phenotypic variation in field environments and 56% under controlled environmental conditions (CEC). qRphND was mapped to chromosome 6HL and had smaller effect. The qRphFlag resistance allele was common in leaf rust resistant cultivars derived from Vada and Emir and has been designated Rph20, the first gene conferring APR to P. hordei to be characterized in barley. Three QTL contributing partial resistance to B. graminis were detected in at least two of the three test environments. All three QTL were donated by Flagship and were mapped to chromosomes 3H, 4H and 5H (5HS) accounting for up to 18.6%, 3.4% and 8.8% phenotypic variation, respectively. The 5HS QTL contributed partial resistance to B. graminis in all field environments and aligned with the genomic region of Rph20. Despite both parental lines being non-dormant, some DH lines displayed moderate to high levels of grain dormancy. Two QTL for grain dormancy were indentified that were detected consistently across three environments; qSDFlag and qSDND (donated by Flagship and ND24260, respectively). qSDFlag was positioned close to the centromeric region of chromosome 5H (accounting for up to 15% of the phenotypic variation), whereas qSDND had larger effect (accounted for up to 35% of the phenotypic variation) and was mapped to chromosome 5HL; positioned proximal and independent to the well-characterized “SD2 region” that is associated with both high levels of dormancy and with inferior malt quality. DH lines were assigned QTL based on marker haplotypes within each of the favourable QTL regions. Based on these haplotypes, three DH lines carrying all six major QTL were identified. However, none of these three DH lines displayed high phenotypic values across multiple environments. Therefore, it appears that additional genes with small effect are required to achieve both high levels of disease resistance and grain dormancy. The implications of these results for breeding programs are discussed. Despite the complex inheritance patterns of these traits, the opportunity remains to accelerate the introgression of multiple target traits into adapted cereal cultivars. Breeding strategies can be built using technologies such as: rapid generation advance under controlled environmental conditions using constant light photoperiod, high-throughput phenotypic screening methods allowing selection for multiple target traits, and application of high-throughput DNA markers for selection of known genes and recovery of the adapted genetic background.
Keyword Barley breeding
durable disease resistance
Puccinia hordei
Blumeria graminis
pre-harvest sprouting
quantitative trait loci
DArT genotyping
phenotypic screening
marker-assisted selection
Additional Notes Colour pages: 63, 66, 70, 92-93, 98-99, 118, 121 Pages 147-154 is landscape.

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Created: Wed, 06 Jun 2012, 13:37:16 EST by Mr Lee Hickey on behalf of Library - Information Access Service