*Email: zhangjinpeng@caas.cn; lilihui@caas.cn

Agropyron cristatum is a valuable wild relative for wheat improvement. Our previous study confirmed that the A. cristatum chromosome 1P carries small flag leaf and dwarf traits in wheat backgrounds. Here, we reported that T1AL·1PS and T1AS·1PL Robertsonian translocations (RobTs) were produced by breakage-fusion mechanism based on wheat-A. cristatum 1P(1A) substitution line II-3-1c.

Combining molecular markers and cytological analysis, we identified 16 spontaneous RobTs from 911 F2 individuals derived from the cross of commercial cultivar Jimai22 and II-3-1c. Fluorescence in situ hybridization was applied to detect the fusion structures of the centromeres in wheat and A. cristatum chromosomes. The whole genome re-sequencing results indicated that the chromosomal junction point was located at the physical position of Triticum aestivum chromosome 1A (212 Mb) and A. cristatum chromosome 1P (230 Mb).

Genomic in situ hybridization in pollen mother cells showed that the produced translocation lines could form stable ring bivalent. Introducing chromosome 1PS translocation fragment into wheat significantly increased the number of fertile tillers, grain number per spike, and grain weight, and reduced the flag leaf area.

However, introducing chromosome 1PL translocation fragment into wheat significantly reduced flag leaf area and plant height with a negative effect on yield components. The pre-breeding two types of spontaneous RobTs T1AL·1PS and T1AS·1PL pave the way for wheat dense planting architecture improvement.