Genetic analysis of crosses between hexaploid bread (Triticum aestivum L.) and tetraploid durum wheat (T. turgidum spp durum)

Genetic analysis of crosses between hexaploid bread
(Triticum aestivum L.) and tetraploid durum wheat
(T. turgidum spp durum)

An ability to access and then transfer genes from bread wheat into durum wheat and viceversa is an excellent way to improve the genetic architecture of these two closely related but a different ploidy level wheat species. Bread wheat has number of desirable characters such as partial resistance to crown rot and head blight that can complement durum wheat. Durum wheat has a number of desirable traits such as seed weight, seed colour, and nematode tolerance that can complement bread wheat. Therefore, developing hexaploid/tetraploid crosses can be one of the useful breeding techniques to addresses bread and durum wheat improvement for yield, pest and disease resistance. Before screening for any traits that have been incorporated from bread and durum wheat into hexaploid/tetraploid derived lines, it is necessary to understand how these inter-ploidy crosses are different with regards to inheritance of the nuclear and cytoplasmic genomes. Thus the present study aimed to screen nuclear and cytoplasmic genome inheritance of different hexaploid/tetraploid wheat crosses.

To determine the proportion of nuclear genome inheritance from either parent of the hexaploid/tetraploid derived wheat lines, high-density polymorphic DArT markers and cytological genomic and fluorescence in situ hybridisation were employed. To investigate the cytoplasmic mitochondrial inheritance, targeted cytochrome maturation genes ccmfn, ccmfc and nad3 genes of bread and durum wheat were sequenced using Sanger sequencing. Different exaploid/tetraploid crosses were established following different breeding techniques, i.e., reciprocal crosses, crosses involving different hexaploid and tetraploid cultivars, crosses made at different time points; and crosses involving a bread wheat cultivar with an introgressed 2G segment. Retention of D-genome chromosomes, proportion of chromosome A and B genome alleles inherited, and how introgressed 2G segment of bread wheat cultivars inherits when combined with tetraploid durum wheat were discussed in different respective research chapters. This thesis also has an additional chapter summarising the maternal inheritance of cytoplasmic DNA in polyploidy crosses. Overall this study has illustrated how hexaploid/tetraploid wheat crosses can be used in the commercial plant breeding programs for bread and durum wheat improvement.