Meiotic behaviour and chromosome inheritance in interspecific hybrids of allotetraploid Brassica species / Annaliese Sarah Mason

2010

[Truncated abstract] Unreduced gametes may provide a route for polyploid formation in Brassica. Following polyploid formation, normal diploid meiosis (without abnormal chromosome associations) must be established in new polyploid species. Interspecific hybrids between the Brassica allotetraploid species B. juncea (2n = 4x = AABB), B. napus (2n = 4x = AACC) and B. carinata (2n = 4x = BBCC) were used to explore these processes, and to test potential mechanisms of polyploid formation in Brassica. Male unreduced gamete production was estimated by the proportion of dyads and giant sporads observed in immature anthers, and by the proportion of giant pollen grains observed in the viable pollen fraction in five genotypes of B. napus, two genotypes of B. carinata, one genotype of B. juncea and in the interspecific hybrids between them. Interspecific hybrids produced higher frequencies of male unreduced gametes as assessed by sporads (average 1.32%, range 0.06 - 3.29%) and in the viable pollen fraction (average 13.8%, range 0.2 - 33.9%) than their parent genotypes (average 0.02% in sporads and average 0.15% in viable pollen). Male unreduced gamete production was also assessed in a subset of five parent and five interspecific hybrid genotypes across four different ambient day/night temperature treatments hot (30 C/20 C), warm (25 C/15 C), cool (18 C/13 C) and cold (10 C/5 C). Two genotypes of B. napus B. carinata hybrids produced elevated levels of male unreduced gametes (23% and 9%) in the cold temperature treatment compared to other temperature treatments (1-4% and 0-2%), but no other genotype was responsive to temperature. A two-step crossing design utilising unreduced gametes was tested for utility in producing allohexaploid Brassica (2n = AABBCC) from intercrossing the three allotetraploid species.

First generation hybrids with genome comple-ments 2n = AABC, 2n = BBAC and 2n = CCAB were produced from pairwise crosses among the three allotetraploid species, then crossed to the third allotetraploid (e.g. B. juncea (AABB) x B. napus (AACC) – > hybrid AABC B. carinata (BBCC)). Unreduced gametes produced by CCAB hybrids were involved in the 2/112 crosses which produced higher ploidy progeny, as assessed by flow cytometry and molecular markers. One of these two progeny was a highly fertile aneuploid (2n = 50) with a near-allohexaploid chromosome complement. Meiosis was observed directly in interspecific hybrid genotypes (genome compositions 2n = AABC, 2n = BBAC and 2n = CCAB) through microscopy and fluorescent labelling of each of the A, B and C Brassica genomes. Meiosis in the interspecific hybrids assessed through fluorescent microscopy showed high levels of abnormal (non-homologous) chromosome pairing between genomes (allosyndesis) and within genomes (autosyndesis). Allosyndesis was observed most frequently as A-C genome associations (mean 4.0 per cell) and less frequently as A-B genome associations (0.8 per cell) and B-C genome associations (0.3 per cell). Autosyndesis occurred most frequently in the haploid A genome (0.75 A-A per cell) and least frequently in the haploid B genome (0.13 B-B per cell). Different genetic factors were implicated in meiotic control of each type of genome association (i.e. A-B, B-C, A-C and autosyndesis)...

Thesis (Ph.D.)--University of Western Australia, 2010

http://repository.uwa.edu.au:80/R/-?func=dbin-jump-full&object_id=30031&silo_library=GEN01