Cytogenetic Behavior of Trigeneric Hybrid Progeny Involving Wheat, Rye and Psathyrostachys huashanica

Trigeneric hybrids are commonly used as bridges to transfer genes from some wild species to cultivated wheat and to measure the genomic interaction between donor species. We previously reported that trigeneric germplasms were produced by crossing wheat-Psathyrostachys huashanica amphiploids (PHW-SA, 2n = 8x = 56, AABBDDNsNs) with hexaploid triticale (Zhongsi 828, 2n = 6x = 42, AABBRR). In the present study, chromosome pairing behavior and the genome constitution of the F4 progenies of wheat-rye-P. huashanica trigeneric hybrids were studied. Cytological analysis showed that the chromosome number of F4 progenies ranged from 39 to 46, and 57.5% of them had 42 chromosomes. The mean meiotic configuration of F4 lines was 1.71 univalents, 20.26 bivalents, 0.04 trivalents, and 0.001 quadrivalents per pollen mother cell. Among the lines with 2n = 42, the average pairing configuration was 1.21 univalents, 16.22 ring bivalents, 4.16 rod bivalents, and 0.01 trivalents. This result indicated that these lines were cytologically stable. Other lines with 2n = 39, 40, 41, 43, 44, 45, and 46, bearing a high number of univalents or multivalents, showed abnormal meiotic behavior. Genomic in situ hybridization (GISH) revealed that all F4 lines had 11-14 rye chromosomes, but no P. huashanica chromosomes. The complete set of 14 rye chromosomes was found in 19 lines. At meiosis, GISH detected 1-6 univalents with hybridization signals of rye in 13 lines. Bivalents with fluorescence signals were identified in each line, ranging from 3 to 7. A quadrivalent with hybridization signals was observed in only 1 line, K13-714-8. Lagging chromosomes, chromosome bridges, micronuclei, and chromosome fragments hybridizing with the probe were not discovered in any of the lines. These results inferred that the behavior of rye chromosomes was normal during meiosis. In addition, 21 lines of 2n = 42 (91.3%) with 12 or 14 rye chromosomes, always contained 6 or 7 bivalents bearing fluorescence signals. This suggested that the rye chromosomes exhibiting complete pairing in these lines were cytologically stable during meiosis and may therefore be considered as new hexaploid triticales. Thus, these lines might be potential materials for further hexaploid triticale improvement.

Correlation between geography and cytogenetic diversity in Pomegranate (Punica granatum L.) cultivars in Iran

Pomegranate (Punica granatum L.) is an important horticultural plant with several cultivated forms planted in different regions of Iran. Due to its economic importance, studies have been carried out to illustrate the genetic diversity at the chromosomal and molecular levels in different pomegranate cultivars growing in this region. This study analyzed chromosome pairing and B-chromosomes of 21 pomegranate cultivars and tried to investigate the effects of geographical parameters like altitude and longitude as well as elevation and the mean annual rainfall on cytogenetic diversity of these taxa. An ANOVA test revealed the presence of a significant difference for chiasmata and chromosome pairing among the cultivars, indicating their genetic differences. A positive significant correlation was observed between total chiasma frequency and terminal chiasmata, intercalary chiasmata and the mean number of quadrivalents. A significant positive correlation was observed between annual rainfall and the mean number of rod bivalents, while a significant negative correlation was found for the number of ring bivalents. Altitude did not show any correlation with the cytogenetic characters studied, but showed a significant negative correlation with the number of univalents. Longitude showed significant positive correlation with the number of ring bivalents and a negative correlation with the number of univalents and intercalary chiasmata. PCA analysis showed that both geographical and cytological features contribute greatly in the diversity observed in the pomegranate cultivars. The occurrence of multipolar cells and unreduced pollen grains were observed in some of the cultivars.

The synaptic behaviour of the wild forms of Triticum turgidum and T. timopheevii

Different wild allopolyploid species of Triticeae show extensive bivalent formation at zygotene while a considerable number of multivalents is present in cultivated polyploid wheats. To study the chromosome behaviour at early meiotic stages in wild forms of tetraploid wheats Triticum turgidum and T. timopheevii (2n = 4x = 28) we have analysed the synaptic pattern in fully traced spread nuclei at mid- and late zygotene and at pachytene of wild accessions of these species. The mean number of synaptonemal complex (SC) bivalents at mid-zygotene ranged from 12.22 to 13.14 among the accessions studied indicating a strong restriction of synapsis initiation to homologous chromosomes. The mean of bivalents increased at pachytene because of the transformation of multivalents into bivalents. Ring bivalents observed at metaphase I support that SC bivalents were formed by homologous chromosomes. The average values of SC bivalents at mid-zygotene in the wild forms are much higher than the average values observed in the cultivated tetraploid wheats but similar to that of a mutant line of T. turgidum with a duplication that includes Ph1, the major homoeologous pairing suppressor locus. These results suggest that the efficiency of the mechanism operating in the homologous recognition for synapsis is higher in wild wheat populations than in cultivated varieties. Apparently, a relatively detrimental modification of the pairing regulating genetic system accompanied the domestication of the wild wheat forms.Key words: Ph1 locus, Triticum turgidum, Triticum timopheevii, synaptonemal complex, diploidisation.

PRODUCTION OF NEW TETRAPLOID TRITICALE FORMS

Attempts were made to produce tetraploid triticales by crossing 6x triticales with diploid rye. In F2, the chromosome number was reduced to between 15 and 23 except in three plants, where the chromosome number was 28, 32 and 38, respectively. An increased frequency of ring bivalents was observed in many F4 plants. In the progeny of the plant with 28 chromosomes, desired plants (four) with 2n = 28 chromosomes were obtained. Data on various agronomic characters were recorded on the progeny of these plants in F5. Reasonably good fertility was noticed in these tetraploid triticale forms.

Cytogenetics of Lathyrus palustris, a natural autohexaploid

American as well as British forms of the perennial plant Lathyrus palustris have 2n = 42 chromosomes with one group of 6 long submetacentric chromosomes, two groups of 6 medium-long subacrocentric chromosomes, three groups of 6 medium-long to medium-short submetacentric to subacrocentric chromosomes, and one group of 6 medium-short metacentric chromosomes. One haploid complement measures 45.8 μm at somatic metaphase. At meiotic first metaphase both forms show extensive multivalent formation. In 50 metaphase I cells of one plant of the British form there were 51 ring hexavalents, 80 chain and open-branched hexavalents of various forms, 2 quinquivalents, 41 ring quadrivalents, 58 chain quadrivalents, 20 branched quadrivalents of various forms, 1 trivalent, 128 ring bivalents, 280 open bivalents, and 9 univalents. It is concluded that L. palustris is most likely a natural autohexaploid with frequent multivalent pairing, many points of pairing initiation, several partner exchanges per multivalent, and many interstitial chiasmata. It may well be the first fully documented true natural autohexaploid reported. Pollen fertility was 56.2% and seed set 37%, apparently sufficient for a perennial plant species.Key words: Lathyrus, natural, autohexaploid, meiosis, multivalents.

Meiotic Behavior and RAPD Segregation in a Tetraploid Hybrid (Vaccinium darrowi × V. corymbosum) Suggests Genomic Divergence in Blueberry

Vaccinium darrowi (D) is a wild blueberry species with low chilling requirements for budbreak, and heat and drought tolerance. Breeding efforts to incorporate these desirable traits into cultivated blueberry (V. corymbosum) (C) would be facilitated with a better understanding of the genomic homology between the two species. An interspecific tetraploid hybrid (CCDD, 2n=4x=48) was used to evaluate genome homology and interspecific recombination. Pollen mother cells examined at diakinesis and early metaphase I exhibited an average of 4.6 chain bivalents, 11.4 ring bivalents, 1.0 chain quadrivalent, and 3.0 ring quadrivalents. This data most closely fits a chromosome pairing model in which there is a greater pairing affinity between homologues than homoeologues. An analysis of the inheritance of 14 RAPD markers unique to V. darrowi in 72 backcross progeny of the V. darrowi–corymbosum hybrid also supported the pairing model: Seven of the 14 markers deviated significantly from tetrasomic inheritance ratios, expected if chromosome pairing was totally random. On the basis of the cytogenetic and RAPD analyses, the genomes of V. darrowi and V. corymbosum are divergent from one another, with preferential pairing within genomes. This outcome suggests there may be difficulty in breaking undesirable linkages when introgressing desirable traits from V. darrowi to V. corymbosum.

Independent arrangement of bivalents and (or) quadrivalents in linear meiotic metaphase plates of rye

The relative positioning of bivalents and (or) quadrivalents in flattened lateral views of metaphase I (linear metaphase plates) has been analyzed in three different plant types of rye: normal plants (type 1); heterozygotes for translocation T305W (type 2); and double heterozygotes for translocations T305W and TR01 (type 3). In all plant types all bivalents and (or) quadrivalents were identified using C-banding. The results indicate that quadrivalents show a preference towards being located in marginal positions of the linear plate, and there are also differences in position preferences between specific bivalents. Adjacently oriented quadrivalents and rod bivalents show a stronger preference for marginal positions than alternate quadrivalents and ring bivalents, respectively, but this does not indicate the existence of a fixed or ordered arrangement of chromosomes in the spindle since bivalents and (or) quadrivalents are independently located relative to each other.Key words: Secale, meiosis, metaphase, arrangement, multivalents, bivalents.