E-mail: d23a3003b@edu.tottori-u.ac.jp

Wheat (Triticum aestivum L., 2n=6x=42, AABBDD) is vulnerable to high temperatures and is severely affected by global warming. There is a need to increase the genetic diversity of bread wheat to adapt to climate change. The use of wild species in bread wheat is one of the most important means of improving wheat. Ae. tauschii (Aegilops tauschii Coss., 2n=2x=14, DtDt) is the D genome doner of wheat.

By crossing wheat directly with Ae. tauschii, synthetic octaploid wheat (2n=8x=56, AABBDDDtDt) can be produced without altering the genetic composition of the wheat AABB genome. This approach is a good strategy to expand the genetic diversity of wheat D genome. In the present study, a Japanese wheat cultivar Norin 61 (N61) and CIMMYT wheat varieties Borlaug 100 (B100) were used as female parents, and 210 lines of Ae. tauschii were used as male for synthetic octaploid wheat production.

The synthetic octaploid wheat will be backcrossed with wheat (N61 or B100) to create lines that possess various Ae. tauschii Dt genome fragments within the wheat N61 or B100 genomic background. So far, forty-five lines of synthetic octaploid wheat with N61 and one line with B100 have been produced. The seed setting rates in the hybridization crosses (i.e., cross ability) varied depending on the crossing combination N61 (0%~56.3%) and B100 (0%~6.3%).

We measured the ploidy levels of 103 plants derived from 40 lines of octaploid wheat by Flow-cytometry. Out of these, 85 plants were octaploid, 16 plants were hexaploid, and 2 plants had the fewer chromosomes than 42 (hexaploidy). These ploidy levels were confirmed by the chromosome counting. These findings suggest that N61 was relatively easy to cross with Ae. tauschii. However, this cross ability was dependent on the genotypes of the male parents of Ae. tauschii.

About 82.5% of octaploid wheat maintained the ploidy and 17.5% of octaploid wheat lost the chromosomes and experienced reduction in their ploidy levels during propagation. We are in the process of producing the backcrossing population to exploit the genetic diversity of Ae. tauschii into bread wheat.