Abstract

The wild relatives of wheat provide an important source of genetic variation for wheat improvement. Much of the work in the past aimed at transferring genetic variation from wild relatives into wheat has relied on the exploitation of the ph1b mutant, located on the long arm of chromosome 5B. This mutation allows homologous recombination to occur between chromosomes from related but different genomes, e.g. between the chromosomes of wheat and related chromosomes from a wild relative resulting in the generation of interspecific recombinant chromosomes. However, the ph1b mutant also enables recombination to occur between the homologous genomes of wheat, e.g. A/B, A/D, B/D, resulting in the generation of wheat intergenomic recombinant chromosomes. In this work we report on the presence of wheat intergenomic recombinants in the genomic background of hexaploid wheat/Amblyopyrum muticum introgression lines. The transfer of genomic rearrangements involving the D-genome through pentaploid crosses provides a strategy by which the D-genome of wheat can be introgressed into durum wheat. Hence, a pentaploid crossing strategy was used to transfer D-genome segments, introgressed with either the A- and/or the B-genome, into the tetraploid background of two durum wheat genotypes Karim and Om Rabi 5 in either the presence or absence of different Am. muticum (2n = 2x = 14, TT) introgressions. Introgressions were monitored in backcross generations to the durum wheat parents via multi-color genomic in situ hybridization (mc-GISH). Tetraploid lines carrying homozygous D-genome introgressions, as well as simultaneous homozygous D- and T-genome introgressions, were developed. Introgression lines were characterized via Kompetitive Allele-Specific PCR (KASP) markers and multi-color fluorescence in situ hybridization (FISH). Results showed that new wheat sub-genomic translocations were generated at each generation in progeny that carried any Am. muticum chromosome introgression irrespective of the linkage group that the segment was derived from. The highest frequencies of homologous recombination were observed between the A- and the D-genomes. Results indicated that the genotype Karim had a higher tolerance to genomic rearrangements and T-genome introgressions compared to Om Rabi 5. This indicates the importance of the selection of the parental genotype when attempting to transfer/develop introgressions into durum wheat from pentaploid crosses.

Highlights

  • The most important cultivated Triticum species are hexaploid bread wheat (2n = 2x = 42; AABBDD, Triticum aestivum L. ssp. aestivum) and tetraploid durum wheat (2n = 2x = 28; AABB, Triticum turgidum L. ssp. durum)

  • This paper describes the introgression of both wheat inter-genome rearrangements involving the D-genome and T-genome segments of Am. muticum present in hexaploid wheat/Am. muticum introgression (WMI) lines into two durum wheat genotypes using pentaploid crosses

  • Pentaploid crosses between bread and durum wheat have previously been shown to generate viable F1 seed that can be used in a backcrossing programme to either of the parents (Eberhard et al, 2010; Martin et al, 2013; Kalous et al, 2015)

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Summary

Introduction

The most important cultivated Triticum species are hexaploid bread wheat Tetraploid wheat arose 500,000 years ago from a cross between the wild ancestors of the A-genome, Triticum urartu Thum ex. The addition of the D-genome to hexaploid wheat conferred baking characteristics and a wide climatic adaptation compared to durum wheat (Zohary et al, 1969) resulting in bread wheat becoming one of the most widely grown crops due to its high yields and nutritional and processing qualities (Shewry and Hey, 2015). The incorporation of new alleles into wheat germplasm is considered essential for the continued improvement of durum wheat productivity

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