María Rosa Ferrari

Cytological analysis of hybrids among triticales and trigopiros

We studied three different tricepiros: (Don Santiago x Don Noé), (Cumé x Horovitz) and (Cumé x Don Noé). The tricepiro (Don Santiago x Don Noé) was obtained by crossing the triticale Don Santiago INTA (AABBRR, 2n = 6x = 42) with the trigopiro Don Noé INTA (AABBDDJJ, 2n = 8x = 56). The number of chromosomes for the F1 was 2n = 49, the most frequent meiotic configuration being 14 bivalents and 21 univalents. The univalents were situated in the periphery of the equatorial plane, whereas the bivalents were located in the central zone. The chromatids in some of the univalents split when bivalents underwent reductional division in anaphase I. There were few laggard chromosomes or chromatids at this phase. The number of chromosomes (2n = 48-58) was high and variable, and the number of bivalents per cell (18-23) also high in F 3 individuals. In all F 8 tricepiros (Don Santiago x Don Noé), F 12 tricepiros (Cumé x Horovitz) and F 12 tricepiros (Cumé x Don Noé), the number of chromosomes (2n = 42) was the same, these retaining the rye genome, as demonstrated by GISH and FISH. These new synthesized allopolyploids constitute interesting models for investigating the evolutionary changes responsible for diploidization, and the chromosomal and genomic re-ordering that cannot be revealed in natural allopolyploids.

Variability in the amount of homoeologous pairing among F1 hybrids

Genes involved in the exclusive pairing of homologous chromosomes have been described in several polyploid species but little is known about the activity of these genes in diploids (which have only one dose of each homoeologous genome). Analysis of the meiotic behaviour of species, natural and artificial hybrids and polyploids of Glandularia suggests that, in allopolyploids where homoeologous genomes are in two doses, regulator genes prevent homoeologous pairing. The different meiotic phenotypes in diploid F1 hybrids between Glandularia pulchella and Glandularia incisa strongly suggest that these pairing regulator genes possess an incomplete penetrance when homoeologous genomes are in only one dose. Moreover, the meiotic analysis of natural and artificial F1 hybrids suggests that the genetic constitution of parental species influences the activity of pairing regulator genes and is mainly responsible for variability in the amount of homoeologous pairing observed in diploid hybrids. In Glandularia, the pairing regulator genes originated in South American diploid species. The cytogenetic characteristics of this genus make it a good model to analyse and explore in greater depth the activity of pairing regulator genes at different ploidy levels.

Nucleolar activity in Triticum x Thinopyrum hybrids with different ploidy level

Abstract The activity of nucleolar organizer regions (NORs) and the presence of ribosomal DNA (rDNA) zones were studied in two Triticum x Thinopyrum hybrids: a hexaploid hybrid with 2n = 42 chromosomes, named trigopiro SH16 INTA, and a decaploid hybrid with 2n = 56 chromosomes, named trigopiro Don Noé INTA. The use of the pTa71 probe revealed the presence of 10 rDNA signals in both hybrids, whereas the Ag-NORs technique showed 10 signals in SH16 and 8 in Don Noé. We concluded that all trigopiro SH16 INTA NORs are active and that the activity of one NOR pair of trigopiro Don Noé INTA is suppressed. Therefore, the amphiplasty phenomenon is present in trigopiro Don Noé INTA but not in trigopiro SH16 INTA.

HETEROCROMATINA TELOMÉRICA, SEMILLAS Y CARACTERÍSTICAS MEIÓTICAS EN DOS LÍNEAS DE TRICEPIRO

A hybrid, named tricepiro, was obtained in 1972, by crossing a hexaploid triticale (2n=6x=42) and an octoploid trigopiro (2n=8x=56). The lines achieved include the tricepiro Don Rene INTA, which has shriveled kernels, and FA-L2, which has smooth ones. The relationship between the heterochromatin content of the rye chromosomes, the seed weight, the presence of meiotic abnormalities and the kernel shriveling has been documented previously in other intergeneric hybrids. The purpose of this study was to determine the average percentage of heterochromatin content in the rye chromosomes of the two tricepiro lines mentioned above and to relate this feature to some characteristics of the meiosis and seeds. We confirmed that the two lines have the same total chromosome number (2n=42) and the same number of rye chromosomes (14). We found that both lines have a complete chromosome mating until late diakinesis, but differ in the percentage of cells with univalents outside the equatorial plate in Metaphase I (Don Rene 42.85% and FA-L2 14.00%). In addition, the two lines differed in their meiotic index (Don Rene 66.47% and FA-L2 87.90%) and seed weight (Don Rene 0.029 ± 0.000 g and FA-L2 0.038 ± 0.001 g). The C-banding in rye chromosomes in mitotic metaphase indicated that the average percentage of heterochromatin content did not differ significantly between the two lines. In contrast to our expectations, the meiotic behavior and seed characteristics were not related to the heterochromatin percentage of the rye chromosomes of the tricepiro lines studied.