New broad-spectrum resistance to septoria tritici blotch derived from synthetic hexaploid wheat

Septoria tritici blotch (STB), caused by the ascomycete Mycosphaerella graminicola, is one of the most devastating foliar diseases of wheat. We screened five synthetic hexaploid wheats (SHs), 13 wheat varieties that represent the differential set of cultivars and two susceptible checks with a global set of 20 isolates and discovered exceptionally broad STB resistance in SHs. Subsequent development and analyses of recombinant inbred lines (RILs) from a cross between the SH M3 and the highly susceptible bread wheat cv. Kulm revealed two novel resistance loci on chromosomes 3D and 5A. The 3D resistance was expressed in the seedling and adult plant stages, and it controlled necrosis (N) and pycnidia (P) development as well as the latency periods of these parameters. This locus, which is closely linked to the microsatellite marker Xgwm494, was tentatively designated Stb16q and explained from 41 to 71% of the phenotypic variation at seedling stage and 28–31% in mature plants. The resistance locus on chromosome 5A was specifically expressed in the adult plant stage, associated with SSR marker Xhbg247, explained 12–32% of the variation in disease, was designated Stb17, and is the first unambiguously identified and named QTL for adult plant resistance to M. graminicola. Our results confirm that common wheat progenitors might be a rich source of new Stb resistance genes/QTLs that can be deployed in commercial breeding programs

Estimation and utilisation of glutenin gene effects from the analysis of unbalanced data from wheat breeding programs

Glutenins are a major determinant of dough characteristics in wheat. These proteins are determined by genes at 6 loci (Glu genes), with multiple alleles present in most breeding programs. This study was conducted to determine whether estimates of allele effects for the important dough rheological characters, maximum dough resistance (Rmax) and dough extensibility, could be determined from aggregated data from southern Australian wheat breeding programs using statistical techniques appropriate for unbalanced data. From a 2-stage analysis of 3226 samples of 1926 cultivars and breeding lines, estimates of Rmax and extensibility effects were obtained, first for the lines, and then for 31 glutenin alleles. Glutenin genes did not determine flour protein concentration, and this character was used as a covariate. Rankings of the estimates of Rmax for the alleles were similar to the relative scores for dough strength reported from previous studies, providing strong evidence that the analysis of a large, unbalanced data set from applied wheat breeding programs can provide reliable estimates. All 2-way interactions between loci were present for 18 of the alleles. Analyses including interactions showed that epistasis was important for both Rmax and extensibility, especially between the Glu-B1 locus coding for high molecular weight glutenins and the Glu-A3 and Glu-B3 loci coding for low molecular weight glutenins. Because of the complexity of these interactions, similar values of Rmax and extensibility were predicted for diverse combinations of alleles. This implied that the practical application of glutenin genes in applied wheat breeding would be greatly enhanced by computer software which can predict dough rheology characteristics from glutenin allele classifications.H. A. Eagles, G. J. Hollamby, N. N. Gororo and R. F. Eastwoo

Use of triticum tauschii to improve yield of wheat in low-yielding environments

Triticum tauschii (Coss.) Schmal. is an ancestor of bread wheat (T. aestivum). This species has been widely used as a source of simply-inherited traits, but there are few reports of yield increases due to introgression of genes from this species. Selections from F₂-derivedlines of backcross derivatives of synthetic hexaploid wheats (T.turgidum / T. tauschii) were evaluated for grain yield in diverse environments in southern Australia. Re-selections were made in the F₆ generation and evaluated for grain yield, yield components including grain weight, and grain growth characters in diverse environments in southern Australia and north-western Mexico. Re-selection was effective in identifying lines which were higher yielding than the recurrent parent, except in full-irrigation environments. Grain yields of the selected derivatives were highest relative to the recurrent parent in the lowest-yielding environments, which experienced terminal moisture deficit and heat stress during grain filling. The yield advantage of the derivativesin these environments was not due to a change in anthesis date orgrain-filling duration, but was manifest as increased rates of grain-filling andlarger grains, indicating that T. tauschii has outstanding potential forimproving wheat for low-yielding, drought-stressed environments.N.N. Gororo, H.A. Eagles, R.F. Eastwood, M.E. Nicolas and R.G. Floo

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.H. A. Eagles, Karen Cane, Haydn Kuchel, G. J. Hollamby, Neil Vallance, R. F. Eastwood, N. N. Gororo, and P. J. Marti

Ppd1, Vrn1, ALMT1 and Rht genes and their effects on grain yield in lower rainfall environments in southern Australia

Allele-specific markers for important genes can improve the efficiency of plant breeding. Their value can be enhanced if effects of the alleles for important traits can be estimated in identifiable types of environment. Provided potential bias can be minimised, large, unbalanced, datasets from previous plant-breeding and agronomic research can be used. Reliable, allele-specific markers are now available for the phenology genes Ppd-D1, Vrn-A1, Vrn-B1 and Vrn-D1, the aluminium-tolerance gene TaALMT1, and the plant-stature genes Rht-B1 and Rht-D1. We used a set of 208 experiments with growing-season rainfall of <347 mm from southern Australia to estimate the effects of seven frequent combinations of the phenology genes, an intolerant and a tolerant allele of TaALMT1, and two semi-dwarf combinations Rht-B1b + Rht-D1a (Rht-ba) and Rht-B1a + Rht-D1b (Rht-ab) on grain yield in lower rainfall, Mediterranean-type environments in southern Australia. There were 775 lines in our analyses and a relationship matrix was used to minimise bias. Differences among the phenology genes were small, but the spring allele Vrn-B1a might be desirable. The tolerant allele, TaALMT1-V, was advantageous in locations with alkaline soils, possibly because of toxic levels of aluminium ions in subsoils. The advantage of TaALMT1-V is likely to be highest when mean maximum temperatures in spring are high. Rht-ab (Rht2 semi-dwarf) was also advantageous in environments with high mean maximum temperatures in spring, suggesting that for these stress environments, the combination of Vrn-B1a plus TaALMT1-V plus Rht-ab should be desirable. Many successful cultivars carry this combination.A. Eagles, Karen Cane, Ben Trevaskis, Neil Vallance, R. F. Eastwood, N. N. Gororo, Haydn Kuchel and P. J. Marti

Ppd-B1 and Ppd-D1 and their effects in southern Australian wheat

Photoperiod and vernalisation genes are important for the adaptation of wheat to variable environments. Previously, using diagnostic markers and a large, unbalanced dataset from southern Australia, we estimated the effects on days to heading of frequent alleles of Vrn-A1, Vrn-B1, and Vrn-D1, and also two allelic classes of Ppd-D1. These genes accounted for ~45% of the genotypic variance for that trait. We now extend these analyses to further alleles of Ppd-D1, and four alleles of Ppd-B1 associated with copy number. Variation in copy number of Ppd-B1 occurred in our population, with one to four linked copies present. Additionally, in rare instances, the Ppd-B1 gene was absent (a null allele). The one-copy allele, which we labelled Ppd-B1b, and the three-copy allele, which we labelled Ppd-B1a, occurred through a century of wheat breeding, and are still frequent. With several distinct progenitors, the one-copy allele might not be homogenous. The two-copy allele, which we labelled Ppd-B1d, was generally introduced from WW15 (syn. Anza), and the four-copy allele, which we labelled Ppd-B1c, came from Chinese Spring. In paired comparisons, Ppd-B1a and Ppd-B1c reduced days to heading, but Ppd-B1d increased days to heading. Ppd-D1a, with a promoter deletion, Ppd-D1d, with a deletion in Exon 7, and Ppd-D1b, the intact allele, were frequent in modern Australian germplasm. Differences between Ppd-D1a and Ppd-D1d for days to heading under our field conditions depended on alleles of the vernalisation genes, confirming our previous report of large epistatic interactions between these classes of genes. The Ppd-D1b allele conferred a photoperiod response that might be useful for developing cultivars with closer to optimal heading dates from variable sowing dates. Inclusion of Ppd-B1 genotypes, and more precise resolution of Ppd-D1, increased the proportion of the genotypic variance attributed to these vernalisation and photoperiod genes to ~53%.Karen Cane, H. A. Eagles, D. A. Laurie, Ben Trevaskis, Neil Vallance, R. F. Eastwood, N. N. Gororo, Haydn Kuchel and P. J. Marti