Cytogenetic evidence for genome elimination during microsporogenesis in interspecific hybrid between Brachiaria ruziziensis and B. brizantha (Poaceae)

Andréa Beatriz Mendes-Bonato,Cacilda Borges Do Valle,Maria Suely Pagliarini,Claudicéia Risso-Pascotto

doi:10.1590/s1415-47572006000400021

Andréa Beatriz Mendes-Bonato, Cacilda Borges Do Valle + Show 2 more

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https://doi.org/10.1590/s1415-47572006000400021

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Abstract

Microsporogenesis was analyzed in an interspecific hybrid between an artificially tetraploidized sexual accession of Brachiaria ruziziensis (R genome) and a natural apomictic tetraploid accession of B. brizantha (B genome). Chromosomes associated predominantly as bivalents. From this phase to the end of meiosis, chromosomes presented irregular segregation and abnormal arrangement in the metaphase plate. During metaphase I, in 27.8% of meiocytes, bivalents were distributed in two metaphase plates. In anaphase I, two distinct and typical bipolar spindles were formed. In 29.7% of pollen mother cells, one genome did not divide synchronically, with chromosomes lagging behind or not segregating at all. The second division was very irregular, resulting in polyads. Based on previous results from analysis of a triploid hybrid between these species, where the R genome was eliminated by asynchrony during meiosis, it is suggested that the laggard genome in this hybrid also belongs to B. ruziziensis.

Highlights

Microsporogenesis was analyzed in an interspecific hybrid between an artificially tetraploidized sexual accession of Brachiaria ruziziensis (R genome) and a natural apomictic tetraploid accession of B. brizantha (B genome)
The methodology is based on the assumption that the extent of chromosome pairing in hybrids reflects the degree of relationship between the parental species (Dewey, 1982)
In the present hybrid, based on the frequency of chromosome association, the probability of inter-genomic recombination is low since multivalents were rare. Their arrangement in two distinct metaphase plates with nine bivalents in each one suggests that chromosome pairing occurred within genomes, i.e., the eighteen chromosomes of the R genome paired in nine bivalents, and the eighteen chromosomes of the B genome did the same. Such a bivalent disposition in the metaphase plate was never reported in hybrids between other accessions of the Brachiaria species under analysis or in other interspecific hybrids of other genera of higher plants

Summary

Introduction

Microsporogenesis was analyzed in an interspecific hybrid between an artificially tetraploidized sexual accession of Brachiaria ruziziensis (R genome) and a natural apomictic tetraploid accession of B. brizantha (B genome). The degree of genetic divergence between polyploid hybrids is displayed in chromosome pairing, which reflects genome affinity (Sundberg et al, 1991). In the cells with two metaphase plates, chromosome segregation was quite regular in each genome (Figure 1e), with only a

Results

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