Cytological, genetic and agronomic characterization of a barley reciprocal translocation

Reciprocal translocations (RT) are one of the most common structural chromosomal rearrangements occurring in plant species. Spontaneous RT are extremely uncommon in cultivated barley. In fact, ‘Albacete’ is the only extensively cultivated barley variety known to carry a RT without any major reduction in fitness. Previous results have shown that 1H and 3H chromosomes are involved in this translocation which may have a potential interest for plant breeding. A depth understanding of this RT could allowed us to know whether this translocation is involved or not in their drought tolerance and find some interesting phenotypic attributes that could be transfer to other barley genotypes to develop specific germoplasm adapted to stress. In a first step, a set of 230 doubled haploid lines derived from the cross between ‘Albacete’ and the non-translocation barley variety ‘Barberousse’ was used to develop a statistical-genetic approach for the construction of a linkage maps in populations obtained from RT heterozygotes. A preliminary linkage study revealed six main linkage groups, compared to the seven linkage groups on the barley consensus map. One of the linkage groups contained markers of chromosomes 1H and 3H. This union was due to the presence of a RT between chromosomes 1H and 3H in the variety ‘Albacete’. The results of this study revealed that the position of the translocation breakpoints was placed around the centromeric regions for both chromosomes. In a second step, a combination of cytological and molecular genetic approaches was used in order to know how large the segments are that are involved in the interchange between the two chromosomes. The results obtained in this study indicate that the translocation is quite large with breakpoints located on the long arms of chromosomes 1H and 3H resulting in the RT 1HS.1HL-3HL and 3HS.3HL-1HL. The gene content around the translocation breakpoints was estimated at approximately 1,100 and 710 gene models for 1H and 3H, respectively. A large number of doubled haploid lines derived from four crosses involving ‘Albacete’ as one of the parents were used to phenotypically characterize the effects of the RT on some interesting agronomic traits.The results suggested that the RT alone is not causing the drought tolerance of ‘Albacete’; thousand kernel weight is the only trait which is clearly enhanced in the lines carrying the RT. Further work combining the results from this study with QTL analysis was carried out to phenotypically characterize the effects of the reciprocal translocation and QTL simultaneously. For that, an integrated map was constructed making used of a modified version of an algorithm developed by Jansen (2005). Finally, specific QTL methodology for the simultaneous analysis of these interconnected populations was developed; two traits: days to heading (independent of the RT) and thousand kernel weight (affected by the RT) were used as an example.