Transfer of the ph1b Deletion Chromosome 5B From Chinese Spring Wheat Into a Winter Wheat Line and Induction of Chromosome Rearrangements in Wheat-Aegilops biuncialis Hybrids

Abstract

Effective utilization of genetic diversity in wild relatives to improve wheat requires recombination between wheat and alien chromosomes. However, this is suppressed by the <i>Pairing homoeologous gene, Ph1</i>, on the long arm of wheat chromosome 5B. A deletion mutant of the <i>Ph1</i> locus (<i>ph1b</i>) has been used widely to induce homoeologous recombination in wheat × alien hybrids. However, the original <i>ph1b</i> mutation, developed in Chinese Spring (CS) background has poor agronomic performance. Hence, alien introgression lines are first backcrossed with adapted wheat genotypes and after this step, alien chromosome segments are introduced into breeding lines. In this work, the <i>ph1b</i> mutation was transferred from two CS<i>ph1b</i> mutants into winter wheat line Mv9kr1. Homozygous genotypes Mv9kr1 <i>ph1b</i>/<i>ph1b</i> exhibited improved plant and spike morphology compared to Chinese Spring. Flow cytometric chromosome analysis confirmed reduced DNA content of the mutant 5B chromosome in both wheat genotype relative to the wild type chromosome. The <i>ph1b</i> mutation in the Mv9kr1 genotype allowed wheat-alien chromosome pairing in meiosis of Mv9kr1<i>ph1b</i>_K × <i>Aegilops biuncialis</i> F₁ hybrids, predominantly with the M^b-genome chromosomes of <i>Aegilops</i> relative to those of the U^b genome. High frequency of wheat-<i>Aegilops</i> chromosome interactions resulted in rearranged chromosomes identified in the new Mv9kr1<i>ph1b</i> × <i>Ae. Biuncialis</i> amphiploids, making these lines valuable sources for alien introgressions. The new Mv9kr1<i>ph1b</i> mutant genotype is a unique resource to support alien introgression breeding of hexaploid wheat.