Chromosome stability of synthetic Triticum turgidum-Aegilops umbellulata hybrids

Abstract

Background: Unreduced gamete formation during meiosis plays a critical role in natural polyploidization. However, the unreduced gamete formation mechanisms in Triticum turgidum-Aegilops umbellulata triploid F₁ hybrid crosses and the chromsome numbers and compostions in T. turgidum-Ae. umbellulata F₂ still not known.

Results: In this study, 11 T.turgidum-Ae. umbellulata triploid F₁ hybrid crosses were produced by distant hybridization. All of the triploid F₁ 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 F₂ seeds from the triploid F₁ hybrid plants of 10 crosses (no F₂ seeds for STU 16) varied from 35 to 43, and the proportions of euploid and aneuploid F₂ plants were 49.61% and 50.39%, respectively. In the aneuploid F₂ 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.

Conclusion: In the aneuploid F₂ 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 F₂ plants. Furthermore, polymorphic fluorescence in situ hybridization karyotypes for all the U chromosomes were also identified in the F₂ plants when compared with the Ae. umbellulata parents. These results provide useful information for our understanding the naturally occurred T. turgidum-Ae. umbellulata amphidiploids.

Keywords: Turgidum turgidum–Aegilops umbellulata; Chromosome loss and gain; Molecular cytogenetics; Unreduced gametes; Variation in chromosome number and structure.