Premise of research. The fig, Ficus carica (2n=26), is a typical fruit tree of the Mediterranean region where it is cultivated from time immemorial. Because of the scarcity of cytogenetic studies, intraspecific polyploidy in the fig has been overlooked until some years ago when a few 2n=3x=39 genotypes were identified. This finding stimulated further explorations to learn more about the real extent of cytotypic diversity in this species and verify the presence of higher ploidy levels. Methodology. A total of 84 wild fig plants sampled from two different geographic areas was examined for the determination of chromosome numbers and karyotype analyses. The FISH technique using rDNA sequences as probes was applied for a further characterization of the populations and polyploid genotypes discovered. The analysis of the nucleotide composition of 5S rDNA repeats was included in this study to acquire information on the intraspecific variability of F. carica and its genome constitution. Pivotal results. Chromosome counts led to the discovery of additional triploid plants and a new variant with 2n=52 which is the first case of tetraploidy so far reported in F. carica. In contrast to the ploidy level variations the karyotype structure and the distribution pattern of rRNA genes (rDNA) resulted stable. The number of rDNA loci detected in polyploid plants appeared consistent with the number of their respective genomes. The limited heterogeneity of 5S rDNA repeats renders these sequences of little utility for discriminating fig genotypes or populations; however, they could be advantageously used for establishing phylogenetic relationships within the genus and resolving taxonomic questions. Conclusions. The results of this study demonstrate that events of polyploidization in fig are a quite widespread phenomenon, which seems connected to the formation of a triploid cytotype, however the presence of a tetraploid plant suggests a more complex situation which would be interesting to study further. Large scale chromosome investigations would be very helpful in understanding the role of polyploidy in wild and cultivated fig populations.
Recurrent events of polyploidy in Ficus carica L. (Moraceae)
FALISTOCCO, Egizia
2016
Abstract
Premise of research. The fig, Ficus carica (2n=26), is a typical fruit tree of the Mediterranean region where it is cultivated from time immemorial. Because of the scarcity of cytogenetic studies, intraspecific polyploidy in the fig has been overlooked until some years ago when a few 2n=3x=39 genotypes were identified. This finding stimulated further explorations to learn more about the real extent of cytotypic diversity in this species and verify the presence of higher ploidy levels. Methodology. A total of 84 wild fig plants sampled from two different geographic areas was examined for the determination of chromosome numbers and karyotype analyses. The FISH technique using rDNA sequences as probes was applied for a further characterization of the populations and polyploid genotypes discovered. The analysis of the nucleotide composition of 5S rDNA repeats was included in this study to acquire information on the intraspecific variability of F. carica and its genome constitution. Pivotal results. Chromosome counts led to the discovery of additional triploid plants and a new variant with 2n=52 which is the first case of tetraploidy so far reported in F. carica. In contrast to the ploidy level variations the karyotype structure and the distribution pattern of rRNA genes (rDNA) resulted stable. The number of rDNA loci detected in polyploid plants appeared consistent with the number of their respective genomes. The limited heterogeneity of 5S rDNA repeats renders these sequences of little utility for discriminating fig genotypes or populations; however, they could be advantageously used for establishing phylogenetic relationships within the genus and resolving taxonomic questions. Conclusions. The results of this study demonstrate that events of polyploidization in fig are a quite widespread phenomenon, which seems connected to the formation of a triploid cytotype, however the presence of a tetraploid plant suggests a more complex situation which would be interesting to study further. Large scale chromosome investigations would be very helpful in understanding the role of polyploidy in wild and cultivated fig populations.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
