Abstract
Synthetic hexaploid (SH) wheat (AABBD’D’) is developed by artificially generating a fertile hybrid between tetraploid durum wheat (Triticum turgidum, AABB) and diploid wild goat grass (Aegilops tauschii, D’D’). Over three decades, the International Maize and Wheat Improvement Center (CIMMYT) has developed and utilized SH wheat to bridge gene transfer from Ae. tauschii and durum wheat to hexaploid bread wheat. This is a unique example of success utilizing wild relatives in mainstream breeding at large scale worldwide. Our study aimed to determine the genetic contribution of SH wheat to CIMMYT’s global spring bread wheat breeding program. We estimated the theoretical and empirical contribution of D’ to synthetic derivative lines using the ancestral pedigree and marker information using over 1,600 advanced lines and their parents. The average marker-estimated D’ contribution was 17.5% with difference in genome segments suggesting application of differential selection pressure. The pedigree-based contribution was correlated with marker-based estimates without providing chromosome segment specific variation. Results from international yield trials showed that 20% of the lines were synthetic derived with an average D’ contribution of 15.6%. Our results underline the importance of SH wheat in maintaining and enhancing genetic diversity and genetic gain over years and is important for development of a more targeted introgression strategy. The study provides retrospective view into development and utilization of SH in the CIMMYT Global Wheat Program.
Highlights
Umesh Rosyara[1], Masahiro Kishii[1], Thomas Payne[2], Carolina Paola Sansaloni 3, Ravi Prakash Singh 1, Hans-Joachim Braun 1 & Susanne Dreisigacker 1
The current bread wheat D genome has limited genetic diversity due to (a) hexaploid wheat is expected to have evolved from a few hybridization events with Ae. tauschii (b) there has been limited gene flow from Ae. tauschii to bread wheat, both naturally being highly self-pollinated species with inbreeding coefficients ≥90% and (c) intense human selection of bread wheat led to further depletion of diversity[7]
The objectives of our study were to: (a) estimate the genetic contribution of the D’ genome via DartSeq markers in a set of selected synthetic derivative lines and determine its correlation with the expected theoretical contribution calculated using ancestral pedigree information, (b) test if the genetic contribution is disproportionate in different parts of the genome, and (c) measure the theoretical contribution of Synthetic hexaploid (SH) wheat within the best CIMMYT advanced breeding lines distributed in international yield trials over the last 19 years
Summary
Umesh Rosyara[1], Masahiro Kishii[1], Thomas Payne[2], Carolina Paola Sansaloni 3, Ravi Prakash Singh 1, Hans-Joachim Braun 1 & Susanne Dreisigacker 1. The International Maize and Wheat Improvement Center (CIMMYT) has developed and utilized SH wheat to bridge gene transfer from Ae. tauschii and durum wheat to hexaploid bread wheat. This is a unique example of success utilizing wild relatives in mainstream breeding at large scale worldwide. With the development of next-generation sequencing technologies, high-density genome profiling of plant material has become feasible and relatively cost-effective[8,9] These new genotyping technologies have already been effectively used to characterize the genetic diversity in bread wheat[10,11,12]. The D’ genome is assumed to be structurally similar to the D genome, as it has not gone through the same extent of natural and human selection, which results in higher SNP diversity[16]
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