Abstract
Normal pairing and exchanging is an important basis to evaluate the genetic relationship between homologous chromosomes in a wheat background. The pairing behavior between 6V#2 and 6V#4, two chromosomes from different Dasypyrum villosum accessions, is still not clear. In this study, two wheat alien substitution lines, 6V#2 (6A) and 6V#4 (6D), were crossed to obtain the F1 hybrids and F2 segregating populations, and the testcross populations were obtained by using the F1 as a parent crossed with wheat variety Wan7107. The chromosomal behavior at meiosis in pollen mother cells (PMCs) of the F1 hybrids was observed using a genomic in situ hybridization (GISH) technique. Exchange events of two alien chromosomes were investigated in the F2 populations using nine polymerase chain reaction (PCR) markers located on the 6V short arm. The results showed that the two alien chromosomes could pair with each other to form ring- or rod-shaped bivalent chromosomes in 79.76% of the total PMCs, and most were pulled to two poles evenly at anaphase I. Investigation of the F2 populations showed that the segregation ratios of seven markers were consistent with the theoretical values 3:1 or 1:2:1, and recombinants among markers were detected. A genetic linkage map of nine PCR markers for 6VS was accordingly constructed based on the exchange frequencies and compared with the physical maps of wheat and barley based on homologous sequences of the markers, which showed that conservation of sequence order compared to 6V was 6H and 6B > 6A > 6D. In the testcross populations with 482 plants, seven showed susceptibility to powdery mildew (PM) and lacked amplification of alien chromosomal bands. Six other plants had amplification of specific bands of both the alien chromosomes at multiple sites, which suggested that the alien chromosomes had abnormal separation behavior in about 1.5% of the PMCs in F1, which resulted in some gametes containing two alien chromosomes. In addition, three new types of chromosome substitution were developed. This study lays a foundation for alien allelism tests and further assessment of the genetic relationship among 6V#2, 6V#4, and their wheat homoeologous chromosomes.
Highlights
Wheat (Triticum aestivum L. 2n = 6x = 42, AABBDD) is one of the most widely cultivated crops in the world
Pm21, a resistance gene to powdery mildew (PM) from D. villosum, was introgressed into common wheat using chromosome translocation, which was widely used in wheat production and became one of the most effective genetic loci introgressed into wheat from its wild species
We carefully investigated the amplification bands of MBH1 in the F2 populations, and further verified them with the markers N-P4 and N-P5 developed in this study
Summary
There are many genes in wheat relatives with desirable traits, which have great potential to improve the resistance of common wheat to various stresses. D. villosum can, be used as a potential resistance source for wheat breeding [3]. The resistance of the tertiary gene pool of wheat is non-host resistance [4], which is usually wide spectrum and high efficiency. Pm21, a resistance gene to PM from D. villosum, was introgressed into common wheat using chromosome translocation, which was widely used in wheat production and became one of the most effective genetic loci introgressed into wheat from its wild species. More than 300 D. villosum accessions were collected, and four of them were introgressed into wheat as additional lines, substitution lines, or translocation lines [8,9,10,11]
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