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.
Summary. An important limitation to the production of durum wheat in South Australia is its poor adaptation to the alkaline, sodic soils of the cereal belt, which often results in nutrient imbalances in the crop. A field experiment was conducted at Palmer, South Australia, to measure the nutrient uptake and distribution between grain and straw of 3 bread wheat cultivars and 9 cultivars and breeding lines of durum wheat. The purpose of the work was to characterise the patterns of nutrient uptake and to examine whether there were major, consistent differences between bread wheat and durum wheat. Rainfall during the growing season was below average and the crops suffered from drought stress after anthesis. Plants were marginally deficient or deficient in nitrogen (N), phosphorus (P) and zinc (Zn), and boron (B) concentrations were high. Compared with bread wheat, durum wheat had a very much higher concentration of sodium (Na), higher concentrations of calcium (Ca) and sulfur (S), but lower concentrations of potassium (K), magnesium (Mg), manganese (Mn) and copper (Cu). Total amounts of P, Zn and Na in the shoot continued to increase throughout the growing season with significant increases occurring during grain filling, whereas there was little increase in the amount of N, K, B and Mn during grain filling. The maximum rate of nutrient uptake occurred before the time of maximum crop growth rate, and was in the order K (10.1 weeks after sowing), N (10.6), P (11.3), Mn (12.0), Zn (12.5) and B (14.6); maximum growth rate occurred at 14.8 weeks. There was no consistent difference between bread and durum wheat in the partitioning of nutrients to the grain. The importance of N and Zn uptake to the growth of the durum wheat genotypes was shown by significant correlations between maximum uptake rates of these nutrients and maximum crop growth rate, with the strongest correlation being with Zn. Growth rate was not correlated with uptake rates of other nutrients. A number of genotypes of durum wheat had maximum rates of Zn and Mn accumulation up to twice those of the current commercial genotypes. Some of these lines have yielded well at Zn- and Mn-deficient sites which indicates that the micronutrient efficiency of durum can be improved. Late in the season the experiment showed signs of infection by crown rot (Fusarium graminearum Schw. Group 1). Durum wheat showed more severe symptoms than bread wheat and the number of white heads in durum wheat was inversely correlated with the concentration of Zn in the shoot during the pre-anthesis period.
Abstract The changes in nutrient content of grain parts and seedling parts in wheat (Triticum aestivum L. cv RAC655) were followed from germination to early seedling development (8 days). The grain was separated into seed coat, endosperm and embryo and the seedling into roots and shoots. The dry weight of the seed coat did not change throughout the experimental period whereas that of the endosperm rapidly declined from day 4 onwards. The seed coat contained the most nutrients of all grain parts, except for sulphur (S) and nitrogen (N). The endosperm contained between 20–35% of the total grain nutrients (except S, 50%). The embryo generally contained little nutrient, between 4–10%, except for zinc [(Zn) 20%], manganese [(Mn) 17%], and boron [(B) 13%]. Large amounts of potassium (K) were remobilized from the seed coat whereas no magnesium (Mg), Zn, copper (Cu), or B was remobilized. Nutrients were rapidly mobilized from the endosperm, particularly K and S. The shoots generally received a greater proportion of nutrients compared to the roots, except for Zn, Mn, and Cu which were distributed between them evenly. The dynamics of nutrient remobilization are discussed in relation to the distribution of nutrients within the grain and the consequences for early seedling vigor.
Genetic associations of morphological, biochemical, and DNA markers with economically important traits can be used for indirect selection of the traits. Chromosomal linkage between pseudo-black chaff and the stemrust resistance gene Sr2, and between the red glume gene (Rg1) and the stripe rust resistance gene Yr10, have been used in this way for many years. Similarly, linkages between disease resistance genes, such as Sr38,Lr37, and Yr17, have been used to achieve resistance to multiple diseases while selection is performed for resistance to one disease. Alleles at the Glu loci, assessed as protein differences, have been used as predictors of dough strength. More recently, DNA markers have been developed and used, especially to select for resistance to cereal cyst nematode, a trait which is difficult and expensive to assess with conventional bioassays. We found that the major use of DNA markers was for selection for traits of substantial economic importance, which were primarily determined by a single gene, and where the non-marker assay was expensive and unreliable. The other uses of markers were for pyramiding several genes influencing one trait, or for rapid backcrossing.
Doubled haploid populations from 5 carefully selected wheat (Triticum aestivum L.) crosses were established in order to produce genetic maps. The characterisation of the parental material included pedigree analyses to define the extent of the genetic relationships among the lines and to determine the occurrence of alien chromosome segments that may contribute to segregation distortion. The characterisation of the parents also defined the range of grain quality traits that could be examined in the lines derived from each cross. Populations of up to 321 lines were produced using wide cross-mediated doubled haploid production from F1 plants. Assessment of the lines for heterogeneity was carried out using readily identifiable phenotypic markers and electrophoresis of seed storage proteins, with 2.3–11.6% of the lines being removed from further analysis. Segregation distortion was estimated in several populations where sufficient information from genetic markers was available. In a Sunco/Tasman doubled haploid population, heterogeneity was detected between the first 51 lines and the remainder of the mapping population and this could be traced to F1 plants that were produced from an earlier set of crosses. χ2 tests on the mapping data available for the Cranbrook/Halberd, CD87/Katepwa, and Sunco/Tasman doubled haploid populations revealed segregation distortion at rates of 1.8%, 5.1%, and 12.5% respectively. Whereas the wide-cross doubled haploid protocol does not appear responsible for the bulk of the non-Mendelian segregation observed, several potential sources were identified. In particular, clustering of distorted loci at specific chromosome regions appeared to be associated with the presence of alien introgressions in one of the parents. This was especially marked in the Sunco/Tasman population. Providing such distortions are recognised in the models used, these populations provide powerful tools for extensive mapping studies to determine the genetic factors controlling grain quality traits and other wheat characters of interest.
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.
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