Chromosome stability of synthetic Triticum turgidum-Aegilops umbellulata hybrids

Unreduced gamete formation during meiosis plays a critical role in natural polyploidization. However, the unreduced gamete formation mechanisms in Triticum turgidum-Aegilops umbellulata triploid F hybrid crosses and the chromsome numbers and compostions in T. turgidum-Ae. umbellulata F still not known. In this study, 11 T.turgidum-Ae. umbellulata triploid F hybrid crosses were produced by distant hybridization. All of the triploid F hybrids had 21 chromosomes and two basic pathways of meiotic restitution, namely first-division restitution (FDR) and single-division meiosis (SDM). Only FDR was found in six of the 11 crosses, while both FDR and SDM occurred in the remaining five crosses. The chromosome numbers in the 127 selfed F seeds from the triploid F hybrid plants of 10 crosses (no F seeds for STU 16) varied from 35 to 43, and the proportions of euploid and aneuploid F plants were 49.61% and 50.39%, respectively. In the aneuploid F plants, the frequency of chromosome loss/gain varied among genomes. The chromosome loss of the U genome was the highest (26.77%) among the three genomes, followed by that of the B (22.83%) and A (11.81%) genomes, and the chromosome gain for the A, B, and U genomes was 3.94%, 3.94%, and 1.57%, respectively. Of the 21 chromosomes, 7U (16.54%), 5 A (3.94%), and 1B (9.45%) had the highest loss frequency among the U, A, and B genomes. In addition to chromosome loss, seven chromosomes, namely 1 A, 3 A, 5 A, 6 A, 1B, 1U, and 6U, were gained in the aneuploids. In the aneuploid F plants, the frequency of chromosome loss/gain varied among genomes, chromsomes, and crosses. In addition to variations in chromosome numbers, three types of chromosome translocations including 3UL·2AS, 6UL·1AL, and 4US·6AL were identified in the F plants. Furthermore, polymorphic fluorescence in situ hybridization karyotypes for all the U chromosomes were also identified in the F plants when compared with the Ae. umbellulata parents. These results provide useful information for our understanding the naturally occurred T. turgidum-Ae. umbellulata amphidiploids.