Pigments are essential to the life of all living organisms. Animals and plants have been the subjects of basic and applied research with the aim of determining the basis of the accumulation and physiological roles of pigments. In crop species, the edible organs show large variations in colour. In durum wheat grain, which is a staple food for humans, the colour is mainly due to two natural classes of pigment: carotenoids and anthocyanins. The carotenoids provide the yellow pigmentation of the durum wheat endosperm, and consequently of the semolina, which has important implications for the marketing of end products based on durum wheat. Anthocyanins accumulate in the aleurone or pericarp of durum wheat and provide the blue, purple and red colours of the grain. Both the carotenoids and the anthocyanins are known to provide benefits for human health, in terms of decreased risks of certain diseases. Therefore, accumulation of these pigments in the grain represents an important trait in breeding programs aimed at improving the nutritional value of durum wheat grain and its end products. This review focuses on the biochemical and genetic bases of pigment accumulation in durum wheat grain, and on the breeding strategies aimed at modifying grain colour.

Genetic improvement of quality traits of durum wheat achieved in Italy and Spain during the 20th Century was investigated using an historical series of 12 cultivars from each country. The European Union durum wheat quality index increased by 6.25% (0.13% year^–1 in Italian and 0.06% year^–1 in Spanish cultivars). Protein content decreased by ∼10% (–0.14% year^–1 in Italian and –0.19% year^–1 in Spanish cultivars) but protein per ha increased at a rate of 0.35% year^–1 (0.41% year^–1 in Spanish and 0.26% year^–1 in Italian cultivars). Yellow colour index increased by 9.9% (0.15% year^–1 in Italian and 0.10% year^–1 in Spanish cultivars). Test weight and vitreousness did not suffer significant changes over time. Gluten strength increased by 32.1% or 0.54% year^–1 in Italian, and 27.9% or 0.33% year^–1 in Spanish cultivars. Much larger genetic control on gluten strength was found in Italian than in Spanish cultivars. Changes in sedimentation index (41.1% or 0.64% year^–1 in Italy, and 41.6% or 0.49% year^–1 in Spain) were the consequence of the progressive incorporation into recent cultivars of favourable low molecular weight glutenin subunits (LMW-GS). Breeding increased the frequency of the LMW-GS combination aaa, which was present in 75% of all intermediate cultivars and in 100% of the modern Italian cultivars. A LMW-GS combination not previously reported (d?b) was identified in two modern Spanish cultivars. Breeding programs were also successful in increasing the stability of gluten strength and the sedimentation index.

Durum wheat (Triticum turgidum ssp. durum) is typically used to produce pasta. In some parts of the world, it is used to make bread but with inferior loaf volume and texture compared with common wheat bread. This study describes the effect on technological properties of pasta and bread made from durum wheat cv. Svevo (recurrent parent (S), HMW-GS null, 7 8) and two isogenic genotypes carrying pairs of additional subunits 5 10 (S 5 10) or 2 12 (S 2 12), normally present at the Glu-D1 locus in bread wheat. The semolina was re-ground to flour, mixed in various proportions with bakers flour and used to prepare loaves. The dough properties of the S 5 10 line were markedly different from Svevo, having over-strong, stable dough, low wet gluten and elasticity; S 2 12 also displayed stronger dough. Pasta prepared from these genotypes showed lower cooked firmness (adjusted for protein differences), ranked Svevo > S 5 10 = S 2 12. There were no other differences in pasta cooking quality. Bread loaf volume and loaf score decreased as more bakers flour was replaced by durum flour, but the decline varied with the genetic material and dosage. The greatest reduction in loaf volume occurred using S 5 10 and the least with S 2 12, which was similar to Svevo. Bake score was reduced with S 5 10 only. The best loaf was made using Svevo. This work shows that it is possible to manipulate the processing properties of pasta and durum–bread-wheat blends by altering the glutenin subunit composition. This represents an efficient tool to finely manipulate gluten quality in durum wheat.

Glutamine synthetase (GS) enzyme (EC 6.3.1.2) plays a central role in assimilating ammonia produced in the leaf from metabolic processes, spanning from assimilation to transamination reactions and catabolic processes. GS is located in both cytoplasm (GS1, GSe and GSr) and plastids (GS2) of plant cells. Glutamine and glutamate, produced by the concerted action of GS and glutamate synthase, are then transported from the leaf to the developing sinks or grain in wheat. The goal of the present study was to characterise GSe genes and to assess the linkage with grain protein content, an important quantitative trait controlled by multiple genes. Here, we report the isolation of the complete cytosolic GS gene sequences of the durum wheat cvv. ‘Ciccio’ and ‘Svevo’ (characterised by low and high protein content, respectively). GSe-A4 located on 4A chromosome comprises 12 exons separated by 11 introns, while the GSe-B4 gene on 4B chromosome comprises 11 exons separated by 10 introns. Quantitative real-time PCR indicated different expression levels of GSe-A4 and GSe-B4 genes in the two wheat cvv. ‘Ciccio’ and ‘Svevo’. The two GSe genes were significantly associated to quantitative trait loci for grain protein content.

Durum is one of the most susceptible cereals to infection with Fusarium head blight (FHB) due to the lack of resistance sources. Data on the genetic variation and heritability of FHB in elite durum, and especially the new evolving winter durum, are lacking. Thus, we compared 105 elite, winter durum breeding lines with an international collection of 62 old and new winter durum cultivars. We evaluated the development of FHB after inoculation by Fusarium culmorum, heading time, and plant height at three field environments in Germany. Significant genetic variation for FHB was identified in the elite breeding material as well as in the collection. Mean FHB rating was normally distributed with a heritability of >0.7 for both sets, indicating the quantitative genetic nature of the trait. Taking heading time, plant height, and FHB resistance into account, the most interesting genotypes were identified in the elite breeding material. Consequences for the ongoing global efforts for improvement of FHB resistance of durum are discussed.

The Fusarium graminearum species complex (FGSC) is a pathogen of durum wheat and other cereals worldwide. The complex consists of at least 15 species that can produce various mycotoxins, including trichothecenes, associated with human and animals toxicoses. In particular, deoxynivalenol (DON), nivalenol (NIV) and their different acetylated derivatives can be produced by the different chemotypes of the complex. In this study, 90 strains, isolated mainly from wheat in Italy and belonging to the FGSC, were assessed for their phylogeny and their chemotype and trichothecene genotype. Almost all strains of the FGSC belonged to F. graminearum sensu stricto, whereas two strains were F. cortaderiae. On the other hand, all three chemotypes, 3ADON, 15ADON and NIV, occurred; 15ADON was the most common molecular chemotype. The data show that the species composition of the Italian FGSC is homogeneous, whereas wide chemotype variability can occur within F. graminearum sensu stricto.

Durum wheat (Triticum turgidum ssp. durum) is susceptible to Fusarium pseudograminearum and sensitive to zinc (Zn) deficiency in Australian soils. However, little is known about the interaction between these two potentially yield-limiting factors, especially for Australian durum varieties. The critical Zn concentration (concentration of Zn in the plant when there is a 10% reduction in yield) and degree of susceptibility to F. pseudograminearum was therefore determined for five Australian durum varieties (Yawa, Hyperno, Tjilkuri, WID802, UAD1153303). Critical Zn concentration averaged 24.6 mg kg^–1 for all durum varieties but differed for the individual varieties (mg kg^–1: Yawa, 21.7; Hyperno, 22.7; Tjilkuri, 24.1; WID802, 24.8; UAD1153303, 28.7). Zinc efficiency also varied amongst genotypes (39–52%). However, Zn utilisation was similar amongst genotypes under Zn-deficient or Zn-sufficient conditions (0.51–0.59 and 0.017–0.022 g DM μg^–1 Zn, respectively). All varieties were susceptible to F. pseudograminearum but the development of symptoms and detrimental effect on shoot biomass and grain yield were significantly greater in Tjilkuri. Even though crown rot symptoms may still be present, the supply of adequate Zn in the soil helped to maintain biomass and grain yield in all durum varieties. However, the extent to which durum varieties were protected from plant growth penalties due to crown rot by Zn treatment was genotype-dependent.

Stem rust resistance gene Sr13, found frequently in tetraploid wheats, was tested effective against Puccinia graminis f. sp. tritici pathotype Ug99 (TTKSK) and its derivatives. It remains a candidate for developing new cultivars with diverse combinations of stem rust resistance genes. To combine Sr13 with other genes that produce a similar phenotype, linked markers would be required. We used the AFLP approach to identify markers linked closely with Sr13. The STS marker AFSr13, derived from an AFLP fragment, mapped at 3.4–6.0 cM proximal to Sr13 across three mapping populations. Marker dupw167, previously reported to be linked with Sr13, mapped 2.3–5.7 cM distal to Sr13 in four F₃ populations. Marker gwm427 mapped proximal to AFSr13 in two populations, and these markers were monomorphic on one population each. The map order dupw167–Sr13–AFSr13–gwm427 was deduced from the recombination data. Markers dupw167 and AFSr13 were validated on 21 durum wheat genotypes. Combination of dupw167 and AFSr13 would facilitate marker-assisted selection of Sr13 in segregating populations. At the hexaploid level, only gwm427 showed polymorphism and differentiated the presence of Sr13 in 10 of the 15 backcross derivatives carrying Sr13 from their Sr13-lacking recurrent parents.

Dissection of the genetic basis of the adaptive response of durum wheat to unfavourable water and temperature regimes is an important prerequisite for the selection of genotypes less vulnerable to environmental constraints. An elite durum population of 249 recombinant inbred lines was tested across 16 Mediterranean environments characterised by contrasting thermo-pluviometric conditions and, consequently, a broad range of productivity (from 0.56 to 5.88 t  ha^–1). Among the environmental variables investigated, soil moisture during grain filling showed the most consistent correlation with yield components and grain yield, whereas a weaker, albeit in some cases significant, association was noted with temperature at heading and thermal time during grain filling. Ear peduncle length appeared as a valid and easy-to-phenotype morphological proxy for the water available to the plant. In total, 76 quantitative trait loci (QTLs) were identified for yield components and for several morpho-physiological traits (peduncle length, the spectral reflectance index NDVI and leaf greenness at the milk-grain stage expressed in SPAD units) associated with the adaptive response of wheat to water and heat stresses. Although most of the QTLs were significant in only one or two environments, two major QTLs on chromosomes 2BL and 3BS showed consistent additive and epistatic effects on 1000-kernel weight, peduncle length, SPAD values and grain yield in half of the environments. In view of their strong phenotypic effects on kernel weight, these two QTLs are good candidates for positional cloning in order to gain a better understanding of the functional basis of their effect on the plasticity of grain weight and grain yield.

Enlarging the genetic basis of essential crop species such as the polyploid wheats is a priority in breeding outlooks for the new millennium. To this end, one feasible approach to exploit the wide and largely untapped variation present in the gene pools of alien Triticeae species is chromosome engineering, which enables the transfer of alien chromosomal segments carrying targeted genes to wheat chromosomes. Recent progress in molecular marker technology, molecular cytogenetic techniques, and in genome knowledge has greatly enhanced the ability of chromosome engineering to contribute breeder-friendly germplasm, even in the case of durum wheat, considered more sensitive to genome manipulations than bread wheat. Using finely tuned chromosome engineering, stable incorporation into durum has been achieved for various alien segments containing genes for disease resistance, quality attributes, and even yield-related traits, both separately and in combination. The state of the art and the breeding potential of such transfers are reviewed and updated.

A durum wheat TILLING (targeting induced local lesions in genomes) population of 2601 M₃ families was developed from cv. Svevo using ethyl methanesulfonate as a chemical mutagen. The entire M₃ population was field-grown for phenotypic evaluations. Despite the polyploid nature of the wheat genome, a preliminarily phenotypic screening showed a high frequency of morphological alterations (∼22%); specific phenotyping for seed morphology was undertaken. Furthermore, a reverse-genetics experiment was performed on DNA collected from M₂ leaves for the homoeologous genes SBEIIa-A and SBEIIa-B involved in starch metabolism. One non-sense mutation for both genes was identified; specific crosses are planned in order to pyramid the two mutations.