**4. Discussion**

A set of introgression lines involving chromosome 2Hc<sup>h</sup> from *H. chilense* in common wheat background was produced in this work using the gametocidal chromosome 2Cc from *Ae. cylindrica*. Gametocidal genes have been used to produce structural chromosome aberrations in wheat [36,37], barley [38,39] and rye [40]. In *H. chilense*, structural changes have been previously obtained for chromosomes 1Hch, 3Hch, 4Hc<sup>h</sup> and 7Hc<sup>h</sup> [8,11,17,18,41] and have been useful in determining the locations of genes and markers in this species. Breaks at both centromeric and interstitial regions of chromosomes have been induced by gametocidal chromosome 2Cc [36]. In the present study, telocentric and translocations between chromosome 2Hc<sup>h</sup> from *H. chilense* and wheat chromosomes have been generated

Alien addition and translocation lines are an ideal template for PCR-based mapping to assign molecular markers to chromosomes of the wild relatives of wheat [8,11,41–43]. Using gene-based conserved orthologous set (COS) markers on wheat—*H. chilense* introgression lines obtained in this work, we assigned a total of 24 markers to *H. chilense* chromosome 2Hch. A 78.3% transference rate of COS markers to *H. chilense* chromosome 2Hc<sup>h</sup> was found. Since COS markers were intended for comparative studies among grasses, the high rate of transferability obtained in this work was expected [21]. Similar rates of transference of COS markers to *H. chilense* chromosome 7Hc<sup>h</sup> have been found previously [17]. COS markers have also been transferred successfully to other Triticeae species such as *Agropyron cristatum* [29,41] and *Aegilops* spp. [44].

The relevance of chromosome 2Hc<sup>h</sup> for endosperm carotenoid content has been highlighted by previous work. Association studies for YPC allowed the identification of three main chromosome regions for YPC variation in *H. chilense*, with the largest one located on chromosome 2Hc<sup>h</sup> and smaller regions detected on chromosomes 3Hc<sup>h</sup> and 7Hc<sup>h</sup> [20]. Four candidate genes associated with YPC were genetically mapped to chromosome 2Hch: both *Ggpps1* and *Zds* were tightly linked and mapped near the centromere, while *Hyd3* and *Ppo1* were mapped to the long arm of chromosome 2Hc<sup>h</sup> [20]. Furthermore, a significant QTL at the distal part of chromosome 2Hc<sup>h</sup> has also been found where no carotenoid-related genes have been mapped [19,20]. The importance of chromosome 2HchL in grain carotenoid content has also been revealed in the new cereal tritordeum (amphiploid derived from a cross between the wild barley *H. chilense* and durum wheat), which has higher carotenoid pigment content in its grain than durum or bread wheat [45,46].

Chromosome 7Hc<sup>h</sup> from *H. chilense* confers the capacity to accumulate higher carotene concentration in seeds [15]. The *Psy1* gene controlling the first step of the carotenoid biosynthetic pathway was mapped to 7HchS [47]. Wheat—*H. chilense* chromosome 7Hchintrogression lines have been developed [17,18,48], and all the genetic stocks carrying *Psy1* from *H. chilense* show increased carotenoid content relative to common wheat [48,49]. The obtention in this work of translocation T7HchS·2HchL could be of interest for studying the e ffect of the *Psy1* gene located on the 7HchS arm and both the *Hyd3* and *Ppo1* genes mapped to the long arm of chromosome 2Hc<sup>h</sup> [20]. Furthermore, the lines carrying T2HchS·2DL and T2HchS·2DL + T7HchS·D translocations could be of interest for studying the e ffect of both the *Ggpps1* and *Zds* genes mapped to the short arm of 2Hch, in the absence and presence of the *Psy1* gene from *H. chilense*, respectively.

The transference of desirable genes from wild relatives to wheat can be restrict by linkage drag and the lack of compensation for the wheat chromatin substituted. The identification of alien chromosomal regions carrying the genes of interest and the analysis of their homoeologous relationships with wheat chromosomes can overcome that di fficulty. It has been pointed out that only translocations produced by homoeologous recombination are beneficial for wheat improvement [50,51]. In this work, wheat—*H. chilense* macrosyntenic comparisons using COS markers revealed that *H. chilense* chromosome 2Hc<sup>h</sup> exhibits good synteny with wheat homoeologous group 2 chromosomes. Comparative mapping of carotenoid-related genes mapped to chromosome 2Hc<sup>h</sup> also showed good collinearity between *H. chilense* and Triticeae species [20,46]. The 24 COS markers assigned to chromosome 2Hc<sup>h</sup> in this work will facilitate introgression of alien genes associated with this chromosome into wheat.
