The effects of chromosome 6P on fertile tiller number of wheat as revealed in wheat-Agropyron cristatum chromosome 5A/6P translocation lines

KEY MESSAGE : This study explored the genetic constitutions of several wheat- A. cristatum translocation lines and determined the effects of A. cristatum 6P chromosome segments on fertile tiller number in wheat. Progress in wheat breeding is hampered by a relatively narrow range of genetic variation. To overcome this hurdle, wild relatives of common wheat with superior agronomic traits are often used as donors of desirable genes in wheat-breeding programs. One of the successfully utilized wheat wild relatives is Agropyron cristatum (L.) Gaertn (2n = 4x = 28; genomes PPPP). We previously reported that WAT31-13 was a wheat-A. cristatum 5A-6P reciprocal translocation line with higher fertile tiller number and grain number per spike compared to common wheat. However, WAT31-13 was genetically unstable. In this study, we analyzed the 43 genetically stable progenies from WAT31-13 using genomic in situ hybridization, dual-color fluorescence in situ hybridization, and molecular markers. We classified them into three translocation types (TrS, TrL and TrA) and seven subtypes, and also pinpointed the translocation breakpoint. The genotypic data, combined with the phenotypes of each translocation type, enabled us to physically map agronomic traits to specific A. cristatum 6P chromosome arms or segments. Our results indicated that A. cristatum chromosome 6P played an important role in regulating fertile tiller number, and that positive and negative regulators of fertile tiller number existed on the A. cristatum chromosome arm 6PS and 6PL, respectively. By exploring the relationship between fertile tiller number and A. cristatum chromosome segment, this study presented a number of feasible approaches for creation, analysis, and utilization of wheat-alien chromosome translocation lines in genetic improvement of wheat.