I. Barclay

Review of wheat improvement for waterlogging tolerance in Australia and India: the importance of anaerobiosis and element toxicities associated with different soils

BACKGROUND AND AIMS The lack of knowledge about key traits in field environments is a major constraint to germplasm improvement and crop management because waterlogging-prone environments are highly diverse and complex, and the mechanisms of tolerance to waterlogging include a large range of traits. A model is proposed that waterlogging tolerance is a product of tolerance to anaerobiosis and high microelement concentrations. This is further evaluated with the aim of prioritizing traits required for waterlogging tolerance of wheat in the field. METHODS Waterlogging tolerance mechanisms of wheat are evaluated in a range of diverse environments through a review of past research in Australia and India; this includes selected soils and plant data, including plant growth under waterlogged and drained conditions in different environments. Measurements focus on changes in redox potential and concentrations of diverse elements in soils and plants during waterlogging. KEY RESULTS (a) Waterlogging tolerance of wheat in one location often does not relate to another, and (b) element toxicities are often a major constraint in waterlogged environments. Important element toxicities in different soils during waterlogging include Mn, Fe, Na, Al and B. This is the first time that Al and B toxicities have been indicated for wheat in waterlogged soils in India. These results support and extend the well-known interactions of salinity/Na and waterlogging/hypoxia tolerance. CONCLUSIONS Diverse element toxicities (or deficiencies) that are exacerbated during waterlogging are proposed as a major reason why waterlogging tolerance at one site is often not replicated at another. Recommendations for germplasm improvement for waterlogging tolerance include use of inductively coupled plasma analyses of soils and plants.

Comparison of genetic and cytogenetic maps of hexaploid wheat (Triticum aestivum L.) using SSR and DArT markers

A number of technologies are available to increase the abundance of DNA markers and contribute to developing high resolution genetic maps suitable for genetic analysis. The aim of this study was to expand the number of Diversity Array Technology (DArT) markers on the wheat array that can be mapped in the wheat genome, and to determine their chromosomal location with respect to simple sequence repeat (SSR) markers and their position on the cytogenetic map. A total of 749 and 512 individual DArT and SSR markers, respectively, were identified on at least one of four genetic maps derived from recombinant inbred line (RIL) or doubled haploid (DH) populations. A number of clustered DArT markers were observed in each genetic map, in which 20–34% of markers were redundant. Segregation distortion of DArT and SSR markers was also observed in each mapping population. Only 14% of markers on the Version 2.0 wheat array were assigned to chromosomal bins by deletion mapping using aneuploid lines. In this regard, methylation effects need to be considered when applying DArT marker in genetic mapping. However, deletion mapping of DArT markers provides a reference to align genetic and cytogenetic maps and estimate the coverage of DNA markers across the wheat genome.

A PCR-based marker for selection of starch and potential noodle quality in wheat

A strong association between the absence of the granule-bound starch synthase (GBSS) protein for the 4A chromosome of wheat and Japanese Udon noodle quality has been previously described. The aim of this study was to identify a molecular marker linked to the GBSS 4A locus which could be used to identify wheat with the desired texture for Udon noodles. PCR primers were designed to target this gene which gave a 440 bp PCR band, corresponding to the presence or absence of the 4A GBSS gene. Of the 268 genotypes screened with these primers, 267 were correctly identified using the PCR primers. The remaining genotype was shown to be heterogeneous for the marker. The PCR marker test developed has advantages over existing methods used to screen for Udon noodle starch quality as it enables high throughput, accurate tests to be carried out on leaves of young seedlings or mature seed and identify breeding lines that are heterogeneous for the 4A allele which will allow for reselections. Application of this PCR test will speed up selection for Udon noodle quality genotypes and reduce breeding costs for production of noodle wheat varieties. Abbreviations: CTAB, cetyltrimethlammonium bromide; FSV, flour swelling volume; GBSS, granule-bound starch synthase; IEF, isoelectric focusing; PCR, polymerase chain reaction; SDS-PAGE, sodium dodecyl sulfate-polyacrylamide-gel electrophoresis.

A mutation at the Ala122 position of acetohydroxyacid synthase (AHAS) located on chromosome 6D of wheat: improved resistance to imidazolinone and a faster assay for marker assisted selection

A new mutation at the acetohydroxyacid synthase (AHAS) locus on chromosome 6D of wheat was analyzed in detail because it conferred an improved resistance to the imidazolinone group of herbicides. Sequence analysis showed that the mutation was at the Ala122 position (A122T), a position in AHAS which has not to date been identified in imidazolinone resistant wheat lines even though the position has been identified in other plants and is associated with resistance. An allele-specific assay for the mutation (in the wheat line Brookton-8) was developed and used in a genetic analysis. Two mapping populations were analysed and the doubled haploid progeny from the cross Brookton-8 × Clearfield STL proved to be most informative. The AHASAla122 mutation (A122T) was allelic to the AHASSer653 mutation (S653N) in Clearfield STL (Imi1, on chromosome 6D) and hence was assigned to the chromosome 6D locus. The analysis of the doubled haploid lines in the mapping population demonstrated the greater resistance conferred by the A122T mutation because lines from the same cross and carrying either the A122T or S653N mutations could be directly compared.

Haplotype analyses in wheat for complex traits: tracking the chromosome 3B and 7B regions associated with late maturity alpha amylase (LMA) in breeding programs

The quantitative trait loci (QTLs) on chromosomes 7BL and 3BS from Halberd have been used as a major source of tolerance to late maturity α amylase (LMA) within Australian wheat breeding programs. New simple sequence repeat (SSR) markers identified from the sequencing of Bacterial Artificial Chromosome (BAC) clones from the wheat cv. Renan library, and known SSRs, were used to characterise these major QTLs. The reduction or elimination of the LMA defect in wheat cultivars is a major goal for wheat breeding programs and is confounded by the complexity in measuring the trait unambiguously. In this haplotyping study focussing on two significant chromosomal regions, markers and combinations of markers were investigated for their ability to discriminate between 39 Australian and Mexican wheat lines differing in levels of LMA. Genetic relationships among these wheat lines estimated by cluster analysis of molecular marker data were combined with phenotypic information in order to calibrate the genotypes of the wheat lines against their LMA phenotype. It was evident that some SSRs from the respective QTLs had greater discriminating power than others to identify LMA phenotypes. Discrimination was not, however, absolute and a statistical analysis of the data defined a risk factor associated with particular combinations of alleles, for use in early selection or backcrossing.

Marker Implementation in the Department of Agriculture, Western Australia Wheat Breeding Program

Marker Assisted Selection (MAS) is being applied to a large breeding program that makes approximately 3,000 crosses and has a field program of 180,000 plots across 14 sites each year. In the breeding program MAS is seen as complementing the existing screening for yield, quality and disease resistance. This paper describes the experiences of applying MAS, role of MAS in the breeding program, its effect on breeding methodology, and future directions for MAS in the program