Despite a substantial investment in the development of panels of single nucleotide polymorphism (SNP) markers, the simple sequence repeat (SSR) technology with a limited multiplexing capability remains a standard, even for applications requiring whole-genome information. Diversity arrays technology (DArT) types hundreds to thousands of genomic loci in parallel, as previously demonstrated in a number diploid plant species. Here we show that DArT performs similarly well for the hexaploid genome of bread wheat (Triticum aestivum L.). The methodology previously used to generate DArT fingerprints of barley also generated a large number of high-quality markers in wheat (99.8% allele-calling concordance and approximately 95% call rate). The genetic relationships among bread wheat cultivars revealed by DArT coincided with knowledge generated with other methods, and even closely related cultivars could be distinguished. To verify the Mendelian behaviour of DArT markers, we typed a set of 90 Cranbrook x Halberd doubled haploid lines for which a framework (FW) map comprising a total of 339 SSR, restriction fragment length polymorphism (RFLP) and amplified fragment length polymorphism (AFLP) markers was available. We added an equal number of DArT markers to this data set and also incorporated 71 sequence tagged microsatellite (STM) markers. A comparison of logarithm of the odds (LOD) scores, call rates and the degree of genome coverage indicated that the quality and information content of the DArT data set was comparable to that of the combined SSR/RFLP/AFLP data set of the FW map.

The Puccinia striiformis f. sp. tritici (Pst) pathotype, 134 E16A?, detected in 2002 in Australia, produced relatively lower and higher adult plant stripe rust responses, respectively, on cultivars Kukri and Janz in comparison to the pre-2002 Pst pathotype 110 E143A?. Molecular mapping of adult plant stripe rust response variation among 180 Kukri/Janz-derived doubled haploid lines over 4 years, two each with Pst pathotypes 110 E143A? and 134 E16A?, was performed. QYr.sun-7B and QYr.sun-7D were consistently contributed by Kukri and Janz, respectively. QYr.sun-7D corresponded to the genomic location of Yr18 and QYr.sun-7B remains to be formally named. QYr.sun-1B, QYr.sun-5B, and QYr.sun-6B were detected during more than one season irrespective of the Pst pathotypes used, whereas QYr.sun-3B was identified only during the 2003 crop season. QYr.sun-1A contributed by Janz, and QYr.sun-2A from Kukri, were detected only against Pst pathotypes 110 E143A? and 134 E16A?, respectively. The DH lines showing better resistance than the either parent carried combinations of 4 to 6 QTL. These lines are currently being used as stripe rust resistance donors in wheat breeding programs.

Doubled haploids (DHs) are becoming increasingly important in crop breeding programmes but methods for producing oat DHs remain inefficient. In this study haploid and DH oat plants were produced using the oat · maize hybridization method. Factors influencing the rate of caryopsis and haploid embryo production including genotype, post-pollination plant growth regulator application and temperature were investigated. The four growth regulators tested showed significant differences in their capacity to induce caryopsis formation with dicamba producing the highest numbers of caryopses, followed by picloram, 2,4-dichlorophenoxyacetic acid (2,4-D) and gibberellic acid (GA 3 ). No significant differences were observed between these growth regulators for their effect on embryo production. The concentration of dicamba was also important and was found to influence caryopsis but not embryo production, with 50 and 100 mg/l dicamba producing significantly more caryopses than 25 or 5 mg/l. Temperature had a significant impact on both caryopsis and embryo production with the magnitude and direction of response depending on genotype. Rates of haploid embryo production observed were between 0.8% and 6.7% of the pollinated florets. The proportion of haploids, which survived and were successfully doubled with colchicine following transfer to soil was between 72% and 81%.

A white-grained wheat accession, AUS1408, is a current major source of pre-harvest sprouting (PHS) tolerance in Australian breeding programs. This study has located 2 significant quantitative trait loci (QTLs) for its grain dormancy on 4AL and 5BL. Their associations with seed dormancy have been determined from population-level marker-trait associations (with 3 years of phenotype data) and confirmed by transmission/disequilibrium test on selected advanced breeding lines. The 4AL QTL was expressed in all years of testing, with phenotypic variance ranging from 5 to 15%, indicating a strong genotype × environment interaction. This QTL has been reported in wheat cultivars of diverse origin and was also found to be strongly influenced by the environment. The 5BL QTL was found to have a remarkably consistent effect on the trait at a phenotypic variance of around 10%. The successful outcome in this study was facilitated by high throughput DArT mapping, which complemented mapping with microsatellite markers for critical QTL identification. Identification of these QTLs from AUS1408 should enable sprouting tolerance derived from this source to be incorporated into advanced breeding lines, with the use of molecular markers reducing the requirement for multi-year field testing.

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