Australian Wheat Breeding Programs Research Articles

Photoperiod and vernalization gene effects in southern Australian wheat

Photoperiod and vernalization genes are important for the optimal adaptation of wheat to different environments. Diagnostic markers are now available for Vrn-A1, Vrn-B1, Vrn-D1 and Ppd-D1, with all four genes variable in southern Australian wheat-breeding programs. To estimate the effects of these genes on days to heading we used data from 128 field experiments spanning 24 years. From an analysis of 1085 homozygous cultivars and breeding lines, allelic variation for these four genes accounted for ~45% of the genotypic variance for days to heading. In the presence of the photoperiod-insensitive allele of Ppd-D1, differences between the winter genotype and genotypes with a spring allele at one of the genes ranged from 3.5 days for Vrn-B1 to 4.9 days for Vrn-D1. Smaller differences occurred between genotypes with a spring allele at one of the Vrn genes and those with spring alleles at two of the three genes. The shortest time to heading occurred for genotypes with spring alleles at both Vrn-A1 and Vrn-D1. Differences between the photoperiod-sensitive and insensitive alleles of Ppd-D1 depended on the genotype of the vernalization genes, being greatest when three spring alleles were present (11.8 days) and least when the only spring allele was at Vrn-B1 (3.7 days). Because of these epistatic interactions, for the practical purposes of using these genes for cross prediction and marker-assisted selection we concluded that using combinations of alleles of genes simultaneously would be preferable to summing effects of individual genes. The spring alleles of the vernalization genes responded differently to the accumulation of vernalizing temperatures, with the common spring allele of Vrn-A1 showing the least response, and the spring allele of Vrn-D1 showing a response that was similar to, but less than, a winter genotype.

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.

Resistance to the root-lesion nematodePratylenchus thorneiof Iranian landrace wheat

Pratylenchus thornei is widespread throughout the wheat-growing regions in Australia and overseas and can cause yield losses of up to 70% in some intolerant cultivars. The most effective forms of management of P. thornei populations are crop rotation and plant breeding. There have been no wheat accessions identified as completely resistant to P. thornei, therefore breeding programs have used moderately resistant parents. The objective of the present research was to evaluate 274 Iranian landrace wheats for resistance to P. thornei and identify accessions with resistance superior to the current best resistance source (GS50a). Plants were grown in P. thornei inoculated soil under controlled conditions in a glasshouse pot experiment for 16 weeks. Ninety-two accessions found to be resistant or moderately so were retested in a second experiment. From combined analysis of these experiments, 34 accessions were identified as resistant with reproduction factors (final population per kg soil/initial inoculum rate per kg soil) ≤1. In total, 25 accessions were more resistant than GS50a, with AUS28470 significantly (P<0.05) more resistant. The resistant Iranian landraces identified in the present study are a valuable untapped genetic pool offering improved levels of P. thornei resistance over current parents in Australian wheat-breeding programs.

Resistance to the root-lesion nematode Pratylenchus thornei in wheat landraces and cultivars from the West Asia and North Africa (WANA) region

Resistance to the root-lesion nematode Pratylenchus thornei was sought in wheat from the West Asia and North Africa (WANA) region in the Watkins Collection (148 bread and 139 durum wheat accessions) and the McIntosh Collection (59 bread and 43 durum wheat accessions). It was considered that landraces from this region, encompassing the centres of origin of wheat and where P. thornei also occurs, could be valuable sources of resistance for use in wheat breeding. Resistance was determined by number of P. thornei/kg soil after the growth of the plants in replicated glasshouse experiments. On average, durum accessions produced significantly lower numbers of P. thornei than bread wheat accessions in both the Watkins and McIntosh Collections. Selected accessions with low P. thornei numbers were re-tested and 13 bread wheat and 10 durum accessions were identified with nematode numbers not significantly different from GS50a, a partially resistant bread wheat line used as a reference standard. These resistant accessions, which originated in Iran, Iraq, Syria, Egypt, Sudan, Morocco, and Tunisia, represent a resource of resistance genes in the primary wheat gene pool, which could be used in Australian wheat breeding programs to reduce the economic loss from P. thornei.

BAC-derived markers for assaying the stem rust resistance gene, Sr2, in wheat breeding programs

Durable broad-spectrum, adult-plant stem rust resistance in wheat conferred by the Sr2 gene has remained effective against Pucciniagraminis f. sp tritici worldwide for more than 50 years. The Sr2 gene has been positioned on the physical map of wheat to the distal 25% portion of the short arm of chromosome 3B. Selection for this gene in wheat breeding programs within Australia has been performed so far through the use of the linked pseudo black chaff (PBC) phenotype and of the microsatellite markers Xgwm389 and Xgwm533 that flank the gene. The molecular markers flank a genetic interval of approximately 4 cM equating to a physical distance of over 10 Mbp. Recently, a 3B-specific BAC library was developed and a physical map established for this region. Analysis of the sequence of minimal tiling path-BAC clones within the region containing the Sr2 gene enabled the development of three new markers that were mapped within the Xgwm389–Xgwm533 genetic interval and tightly linked to the Sr2 gene. Screening a wide range of germplasm containing the Sr2 gene with these markers demonstrated their usefulness for marker-assisted selection in Australian wheat breeding programs.

The effects on grain quality traits of a grain serpin protein and the VPM1 segment in southern Australian wheat breeding

Production of wheat of sufficient quality to meet market demands is an ongoing agricultural challenge. Identification and evaluation of alleles of genes affecting quality parameters enables breeders to improve their germplasm by active selection towards specific allele combinations. Using a large dataset obtained from southern Australian wheat breeding programs, and including a relationship matrix in the analysis to minimise bias, we re-evaluated the effects of high- and low-molecular-weight glutenin alleles and puroindoline alleles on the grain quality parameters Rmax, dough extensibility, dough development time, flour water absorption, and milling yield and found that estimated effects were in close agreement with those from earlier analyses without a relationship matrix. We also evaluated, for the first time, the effects on the same quality parameters of 2 alleles (wild-type and null) of a defence grain protein, a serpin located on chromosome 5B. In addition, we assessed the effect of the VPM1 alien segment. The serpin null allele significantly reduced milling yield by ~0.4 g of flour per 100 g of grain milled across different germplasm sources and flour protein levels. In Australian germplasm, the origin of this allele was traced to a 19th Century introduction from India by William Farrer; however other sources, of significance in international breeding programs, were also identified. Our analysis of the effect of the VPM1 segment on quality traits revealed no detrimental effects of its presence on the traits we measured.

Global adaptation patterns of Australian and CIMMYT spring bread wheat

The International Adaptation Trial (IAT) is a special purpose nursery designed to investigate the genotype-by-environment interactions and worldwide adaptation for grain yield of Australian and CIMMYT spring bread wheat (Triticum aestivum L.) and durum wheat (T. turgidum L. var. durum). The IAT contains lines representing Australian and CIMMYT wheat breeding programs and was distributed to 91 countries between 2000 and 2004. Yield data of 41 reference lines from 106 trials were analysed. A multiplicative mixed model accounted for trial variance heterogeneity and inter-trial correlations characteristic of multi-environment trials. A factor analytic model explained 48% of the genetic variance for the reference lines. Pedigree information was then incorporated to partition the genetic line effects into additive and non-additive components. This model explained 67 and 56% of the additive by environment and non-additive by environment genetic variances, respectively. Australian and CIMMYT germplasm showed good adaptation to their respective target production environments. In general, Australian lines performed well in south and west Australia, South America, southern Africa, Iran and high latitude European and Canadian locations. CIMMYT lines performed well at CIMMYT's key yield testing location in Mexico (CIANO), north-eastern Australia, the Indo-Gangetic plains, West Asia North Africa and locations in Europe and Canada. Maturity explained some of the global adaptation patterns. In general, southern Australian germplasm were later maturing than CIMMYT material. While CIANO continues to provide adapted lines to northern Australia, selecting for yield among later maturing CIMMYT material in CIANO may identify lines adapted to southern and western Australian environments.

The effect of 3BS locus of Sumai 3 on Fusarium head blight resistance in Australian wheats

The 3BS allele of Sumai 3 has been the main source of Fusarium head blight (FHB) resistance worldwide. Using molecular markers and FHB resistance screenings, we have analysed the effects of this allele in two backcross and two 4-way F2 populations derived from elite Australian cultivars. Compared to individuals without the Sumai 3 allele, individuals with the allele showed an average 32.0% reduction in FHB severity as measured by number of diseased spikelets. This value was slightly reduced to 29.2% when the total number of spikelets was taken into account by expressing severity as the proportion of diseased spikelets. When compared to the parental cultivars, progeny with the 3BS allele of Sumai 3 offered, on average, 43.3% reduction in FHB severity. Significant differences were not detected between progeny that were homozygous or heterozygous for the 3BS locus, indicating a dominant inheritance of this locus. These results confirm that the 3BS allele controls a large component of the FHB resistance in Sumai 3, which can be readily incorporated and detected in backcross populations using molecular markers. The materials derived from this study could offer significant benefits to the Australian wheat breeding programs.

Contributions of glutenin and puroindoline genes to grain quality traits in southern Australian wheat breeding programs

Glutenin genes were known to influence maximum dough resistance (Rmax), dough extensibility (extensibility), and dough development time, whereas puroindoline genes were known to influence grain hardness, flour water absorption (water absorption), and milling yield. These are important determinants of grain quality of wheat in Australia. This study was conducted to investigate the combined effect of these genes on Rmax, extensibility, dough development time, water absorption, and milling yield in a large dataset assembled from the breeding programs based at Horsham, Victoria; Roseworthy, South Australia; and Wagga Wagga, New South Wales; for at least 10 seasons. The effect of the glutenin genes on Rmax, extensibility, and dough development time was confirmed, as was the effect of the puroindoline genes on water absorption and milling yield. In addition, puroindoline genes were shown to significantly affect extensibility and dough development time. The Pina-D1a/Pinb-D1b genotype increased extensibility, dough development time, and milling yield relative to the Pina-D1b/Pinb-D1a genotype. Both of these genotypes are present in cultivars classified as hard-grained in southern Australia. Therefore, the allelic composition of both glutenin and puroindoline genes is required to predict the grain quality of hard wheat in southern Australian breeding programs. The glutenin and puroindoline genes in combination accounted for more than 50% of the genotypic variance for these traits, except for milling yield, but a substantial proportion of the genotypic variation could not be attributed to these genes, indicating that other genes affecting the traits were present in the populations of these wheat-breeding programs.

Using computer simulation of the selection process and known gene information to assist in parental selection in wheat quality breeding

Determining how to choose parents and conduct selections is a critical issue in plant breeding. The genetic and breeding simulation tool QuCim can predict the outcome of a cross under a specific selection scheme, when genetic information for the targetted traits is known. In this paper, we use genetic information from Australian wheat breeding programs about glutenin, as it relates to wheat quality, to predict the outcomes from some example crosses. The 8 Silverstar sister lines used in our study are morphologically very similar, but have different values for 2 important quality traits, maximum dough resistance (Rmax) and extensibility. Supposing we intend to use Silverstar in crosses with other adapted cultivars, without losing grain quality, which sister line should we use? Under the condition that high Rmax is the major breeding objective, QuCim simulation showed that Silverstar 3 and 7 should be chosen if the other parent does not have allele b at Glu-A3 and allele d at Glu-D1. If the other parent has allele b at Glu-A3 and allele d at Glu-D1, all 8 lines can be used. If the other parent does not have allele b at Glu-A3, but has allele d at Glu-D1, Silverstar 3, 4, 7, and 8 should be used, and if the other parent has allele b at Glu-A3, but does not have allele d at Glu-D1, Silverstar 1, 3, 5, and 7 should be used. Therefore, the optimum Silverstar line depends on the alleles present at glutenin loci in the other parent. Australian wheat cultivars Krichauff and Machete have a similar value for Rmax, but they differ substantially as a donor for improving Rmax in other parents. For crosses with Australian wheat cultivar Trident, Machete is the better choice, but for crosses with the Australian wheat cultivar Westonia, Krichauff is better. In conclusion, QuCim can accurately predict the outcome from a specific cross under a selection scheme when gene information is known. It can help breeders identify the best crosses and selection methods to achieve their breeding objectives.

Identification of microsatellite markers associated with the cereal cyst nematode resistance gene Cre3 in wheat

Cereal cyst nematode (CCN) is a root disease caused by the pathogen Heterodera avenae Woll. that significantly reduces wheat (Triticum aestivum L.) grain yields in temperate countries. The Cre3 gene, located on chromosome 2DL, provides high levels of resistance to the Australian pathotype and isolates from Syria and Algeria, and has become available to wheat breeders. Selection for lines carrying the Cre3 gene in Australian wheat breeding programs is currently based on a dominant PCR marker (Cre3spf/r) diagnostic for the Cre3 gene. However, this marker has limitations that increase the cost and reduce selection efficiency in screening early-generation breeding lines. Such limitations would be minimised by the identification of a microsatellite marker linked to the Cre3 gene. We have constructed 2 genetic linkage maps of wheat chromosome 2DL and identified microsatellite markers mapping closely to the diagnostic Cre3spf/r marker. These closely linked markers were validated in a diverse range of germplasm, and one microsatellite marker, Xgwm301, which mapped 4 cM from Cre3spf/r, was shown to be highly associated with the presence of the Cre3 gene. Amplification conditions for the Xgwm301 locus were optimised, and its use in marker-assisted selection to identify Cre3 CCN-resistant wheat in the Australian Grain Technologies breeding program is demonstrated.

Revision of the estimates of glutenin gene effects at the Glu-B1 locus from southern Australian wheat breeding programs

Glutenins are the major determinant of dough characteristics in wheat. These proteins are determined by genes at 6 loci, with multiple alleles present in southern Australian breeding programs. Previously, we estimated the effects of these genes on maximum dough resistance (Rmax), dough extensibility and dough development time. Subsequently, the allele previously classified as Glu-B1b was found to consist of 2 alleles, with one, now considered to be Glu-B1al, producing an overexpression of the Bx7 glutenin subunit. Therefore, there is a potential bias in our previous estimates. An extended dataset was analysed with the 2 alleles now separated. These analyses identified negligible biases in our previous estimates, probably due to a low frequency of Glu-B1al before 1999. However, Glu-B1al produced significantly higher Rmax, dough extensibility, and dough development time values than all other alleles at the Glu-B1 locus. Therefore, at intermediate allele frequencies, substantial bias in estimates of the effects of the Glu-B1 alleles can be expected without correct identification of Glu-B1al.

Genetic and environmental variation for grain quality traits routinely evaluated in southern Australian wheat breeding programs

Milling yield, maximum dough resistance (Rmax), dough extensibility, flour protein concentration (flour protein), particle size index (PSI), water absorption, and dough development time are important determinants of grain quality and are routinely evaluated in Australian wheat breeding programs. Information on allelic variation at the 6 loci determining glutenin proteins is also regularly obtained and used to predict Rmax and extensibility. For each character, except dough development time, 4029 observations on 2377 lines and 94 environments were analysed to estimate genotypic and environmental variances, heritabilities, genotypic and environmental correlations, and the effects of glutenin genes. A subset was analysed for dough development time. Milling yield, Rmax, extensibility, PSI, water absorption, and dough development time had intra-class correlation coefficients, or broad-sense heritabilities, between 0.66 and 0.76, and extensibility had a value of 0.52, with flour protein at 0.36. Genotypic and environmental correlations between extensibility and flour protein were high at +0.78 and +0.85, respectively. Rmax had a genotypic correlation with dough development time of +0.67, which was substantially due to pleiotropic effects of glutenin genes. Rmax, extensibility, PSI, and dough development time were influenced by glutenin genes. For Rmax about 50% of the genotypic variance could be explained by glutenin genes. For extensibility about 50% could be explained by flour protein, with 50% of the remainder by the inclusion of glutenin genes. For dough development time about 15% could be explained by flour protein, with a further 30% by glutenin genes. For PSI, about 40% of the genotypic variation could be accounted for by glutenin genes after the removal of the effects of flour protein and milling yield. We concluded that dough development time could be added to Rmax and extensibility as a trait that can be usefully predicted by the glutenin genes, but more work is required for PSI.

Genetic diversity within Australian wheat breeding programs based on molecular and pedigree data

124 wheat cultivars and breeding lines were screened with 19 microsatellite (SSR) loci generating 160 scorable bands which were used to construct a genetic distance (GD) matrix. A distance matrix based on coefficient of parentage (COP) scores was also generated for the cultivars for which good pedigree records were available. The SSR and COP data for 101 of the wheat cultivars were compared with genetic distance scores obtained using1898 scorable restriction fragment length polymorphism (RFLP) bands previously generated. Phylograms were generated based on the SSR, RFLP,combined SSR and RFLP and COP data. The standardised Mantel's Z test showed that the distance matrices generated from all of the data sets were significantly correlated. Bootstrap analysis showed that, although the SSR and RFLP data were correlated, a large number of SSR loci are required for determining robust genetic relationships between large numbers of cultivars. In addition, accurate pedigree records are needed to determine genetic relatedness using COP. The molecular data were also used to determine the level of genetic variability within breeding programs and to assess the impact of the introduction of semidwarf and other germplasm. The results showed that the level of genetic diversity in Australian wheat cultivars has increased over time and that in particular, the introduction of semidwarf germplasm resulted in an increase in the overall diversity.

Microsatellites as markers for Australian wheat improvement

Microsatellite markers have been shown to be highly polymorphic and simple to use in hexaploid wheat. This study aimed to establish microsatellites as informative markers for Australian wheat improvement. By screening microsatellites developed as part of the Wheat Microsatellite Consortium and other available microsatellite sources, 257 informative microsatellites for Australian wheat varieties were identified and reported in the Australian National Wheat Molecular Marker Program microsatellite database (http://www.scu.edu.au/research/cpcg/). Of these, 151 microsatellites identifying 172 loci were scored on at least 1 of 4 double haploid mapping populations and were then integrated, where possible, into existing genetic maps. Polymorphism information content values were calculated for most microsatellites to establish a reference for their value for future investigations. The mapping of available microsatellites enhances the quality of the genetic maps and may provide useful genetic markers for traits of interest to the Australian wheat breeding programs.

Predicting grain yield in Australian environments using data from CIMMYT international wheat performance trials. 1. Potential for exploiting correlated response to selection

Australian wheat breeding programs are currently evaluating and using advanced breeding lines from the International Centre for Wheat and Maize Improvement (CIMMYT). A more coordinated and efficient procedure for identifying useful lines for Australian breeding programs was evaluated by assessing the potential for exploiting correlated response to selection for grain yield between CIMMYT international and Australian evaluation trials. The genetic correlation, based on 40 common lines, between average line performance across 18 international and six Australian environments was high (0.813±0.049), indicating considerable potential for exploiting correlated response to selection for broad grain yield adaptation to the Australian environments for selection on broad adaptation in the international environments. The potential to select for specific grain yield adaptation to the individual Australian environments was investigated and individual international environments were identified which expressed a higher genetic correlation with the Australian environments than did average performance over all of the international environments. Therefore, opportunity exists for Australian wheat breeders to use the principles of indirect selection to select among advanced CIMMYT wheat lines on grain yield performance in international performance trials for both broad and specific grain yield adaptation to Australian environments prior to the introduction of this material to Australia. Since genotype by environment interaction for yield in the international trials is large and its causes are not well understood, selection for specific adaptation on the results from individual trials will require further investigation of the individual relationships.

Predicting grain yield in Australian environments using data from CIMMYT international wheat performance trials. 2. The application of classification to identify environmental relationships which exploit correlated response to selection

The principles of indirect selection can be used to assess the impact of genotype by environment interaction on selection strategies within breeding programs. The methodology can also be used to assess the opportunity for more efficient acquisition of new germplasm for a breeding program where common genotypes are evaluated in environments sampled by two breeding programs. However, the large number of environmental comparisons that is required complicates this process. To assist environmental comparison, the theory for indirect selection is related to classification methodology for grouping of environments in plant breeding experiments. To demonstrate the application of this methodology, classification was used to jointly group 18 international wheat evaluation environments conducted by the International Centre for Wheat and Maize Improvement (CIMMYT) as part of the 17th International Bread Wheat Screening Nursery (17th IBWSN) and six environments from a trial series conducted in Queensland, Australia using a set of 40 common genotypes. This process was used to identify a subset of international environments which improved indirect response for average grain yield performance in the Australian environments over that for selection on average grain yield performance over all 18 international environments. Similarly, classification was used to identify subsets of international environments which improved indirect response to selection in five of the six Australian environments. More efficient strategies for acquiring useful wheat germplasm for Australian wheat breeding programs from the CIMMYT program by extending this methodology are discussed.