Hybrids between A genome diploid plants from the Chinese and Korean populations of the Scilla scilloides complex were found. Molecular cytogenetic examination and genome size measurement showed that the hybrids were composed of two distinguishable A genomes. Genomic in situ hybridization (GISH) using mixed probes of both parental genomic DNAs could distinguish the chromosomes of each A genome in the chromosome spreads of hybrid plants. This suggests that the A genome plants of the two populations differ at the genomic DNA level. The genome size of the Korean population was 1.2-1.3 times larger than that of the Gansu population according to the area of chromosome set and fluorescence intensity in flow cytometry (FCM). Despite these cytological differences, the hybrids showed normal chromosome pairing in meiosis of pollen mother cells (PMCs), suggesting that the genomes of these two populations still belong to the same genome in terms of classical cytogenetics. Despite these genomes belonging to the same A genome, molecular signs of genome differentiation in the A genome were also found in the 5S rDNA spacer region. Southern blot hybridization of this spacer region from several populations showed that the three A genome populations were distinct from one another. Additionally, in a sequence analysis of a part of matK gene and ITS1, the three A genome populations showed population-specific sequence variations. These results suggest that the A genome populations of S. scilloides is just in the process of genome differentiation.
Unreduced 3x gamete formation of allotriploid hybrid derived from the cross of Primula denticulata (4x) 3 P. rosea (2x) as a causal factor for producing pentaploid hybrids in the backcross with pollen of tetraploid P. denticulata Abstract A triploid hybrid, which was obtained from interspecific crosses between tetraploid Primula denticulata (2n = 4x = 44) and P. rosea (2n = 2x = 22), successfully produced 11 plants by backcrossing with pollen of tetraploid P. denticulata. Analysis of ploidy level using flow cytometry and chromosome counting in the 11 BC 1 plants revealed that all progeny had much larger DNA contents and chromosome number than both parents. In this triploid-tetraploid (3x-4x) crossing, progeny was predominantly true or near pentaploid presumably produced by the fertilization between true or near triploid female gamete produced from triploid hybrid and diploid pollen of tetraploid P. denticulata. These results suggest that unreduced (3x) or near triploid female gametes were partially produced by single step meiosis, either first-division restitution or second-division restitution process. The zygotes formed by the fertilization between true or near triploid egg produced by single step meiosis in triploid hybrid and diploid pollen produced by normal meiosis of tetraploid P. denticulata might be the only survivors in embryogenesis.
In the complex species of Scilla scilloides involving A and B genomes, an amphi diploid having AABB genome composition is a major one of the cytotypes and distributes throughout a growing area of the species. An origin of amphi diploids and whether amphi diploids generated in monophyly or polyphyly are unsolved. In three hybrids with defied combination of genomes a maternal inheritance of chloroplast genome was confirmed in this species. An analysis of matK sequence of chloroplast genome demonstrated that a maternal parent of all amphi diploids in Japan, Korea and Taiwan investigated was a Japanese B genome diploid (BB diploid). In the analysis of ITS1and 5S rDNA of nuclear genome and genome sizes indicated that the paternal parent of amphi diploids was different between the amphi diploid from Japan and Korea, and the amphi diploid from Taiwan. The Japanese and Korean amphi diploids would be originated by a hybridization and subsequent polyploidization between the maternal parent of Japanese BB diploid and the paternal parent of Korean A genome diploid (AA diploid). Taiwanese amphi diploids were generated between the maternal parent of Japanese BB diploid and a paternal parent of AA diploid undiscovered. An event of generation of the amphi diploids in S. scilloides occurred at least twice in the different locations with the different parents.
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