Mitotic and meiotic behavior of rye chromosomes in wheat - Psathyrostachys huashanica amphiploid x triticale progeny

Cytogenetic analysis of meiotic behaviour and stability in a trigeneric hybrid (triticale x trigopiro)

Trigeneric hybrids in Triticeae may help to establish evolutionary relationships among different genomes present in the same cellular genetic background and to transfer different alien characters into cultivated wheat. In the present study, a trigeneric hybrid involving species of Triticum, Secale, and Thinopyrum was synthesized by crossing hexaploid triticale with hexaploid trigopiro. The meiotic behaviour of chromosomes belonging to different genomes was analyzed, using routine and in situ hybridization techniques in F1, F2, and F3 generations of the trigeneric hybrid. The purpose of this study was to determine the chromosome number and genomic constitution and to discuss the mechanisms involved in the stabilization of the artificial tricepiro hybrids. The chromosome number of the trigeneric F1 hybrid was 2n = 42. Between 12 and 16 bivalents were observed in the central zone of the equatorial meiotic plate and between 9 and 18 univalents were found in the periphery of the MI equatorial plate. Seven of these univalents showed hybridization signals with rye DNA. Lagging rye and non-rye chromosomes and separation of sister chromatids were found in anaphase I. Tetrads with a maximum of six micronuclei, with and without hybridization signals of rye DNA, were observed. After three generations, meiotic cells revealed the presence of 42 chromosomes and 21 bivalents in diakinesis cells. The presence of 14 rye (Secale cereale) chromosomes and the complete pairing of chromosomes in F3 hybrids suggest that rye chromosomes would be preferentially transmitted to the progeny and that an elimination mechanism would act on chromosomes of Thinopyrum and wheat D genome.

Karyotypes of Manatees: New Insights into Hybrid Formation (Trichechus inunguis × Trichechus m. manatus) in the Amazon Estuary

Great efforts have been made to preserve manatees. Recently, a hybrid zone was described between Trichechus inunguis (TIN) and the Trichechus manatus manatus (TMM) in the Amazon estuary. Cytogenetic data on these sirenians are limited, despite being fundamental to understanding the hybridization/introgression dynamics and genomic organization in Trichechus. We analyzed the karyotype of TMM, TIN, and two hybrid specimens ("Poque" and "Vitor") by classical and molecular cytogenetics. G-band analysis revealed that TMM (2n = 48) and TIN (2n = 56) diverge by at least six Robertsonian translocations and a pericentric inversion. Hybrids had 2n = 50, however, with Autosomal Fundamental Number (FNA) = 88 in "Poque" and FNA = 74 in "Vitor", and chromosomal distinct pairs in heterozygous; additionally, "Vitor" exhibited heteromorphisms and chromosomes whose pairs could not be determined. The U2 snDNA and Histone H3 multi genes are distributed in small clusters along TIN and TMM chromosomes and have transposable Keno and Helitron elements (TEs) in their sequences. The different karyotypes observed among manatee hybrids may indicate that they represent different generations formed by crossing between fertile hybrids and TIN. On the other hand, it is also possible that all hybrids recorded represent F1 and the observed karyotype differences must result from mechanisms of elimination.

Cytogenetic and agronomic characterization of intergeneric hybrids between Saccharum spp. hybrid and Erianthus arundinaceus

In sugarcane (Saccharum spp. hybrid) breeding, introgression of useful genes via intergeneric hybridization is a powerful strategy for improving the crop productivity. Erianthus arundinaceus shows great potential in terms of useful traits; however, little is known about the cytogenetic and agronomic characteristics of intergeneric hybrids between these two species. Here, we examine the cytogenetic and agronomic characteristics, and relationships between the two in intergeneric F₁ hybrids between modern sugarcane cultivar and E. arundinaceus identified by amplification of 5S rDNA markers and morphological characteristics. The nuclear DNA content of the hybrids varied from 6.07 to 8.94 pg/2C, with intra-clonal variation in DNA content and 5S rDNA sites. Genomic in situ hybridization revealed 53 to 82 chromosomes in the hybrids, with 53 to 56 derived from sugarcane and 1 to 29 from E. arundinaceus. There were significant positive correlations between the number of E. arundinaceus chromosomes and dry matter yield, millable stalk weight, single stalk weight, and stalk diameter, but not sucrose content, reducing sugar content, sucrose/reducing sugar ratio or fiber content. This detailed information on intergeneric F₁ hybrids between modern sugarcane cultivar and E. arundinaceus will contribute to effective utilization of E. arundinaceus in sugarcane breeding.

Divergent Development of Hexaploid Triticale by a Wheat - Rye -Psathyrostachys huashanica Trigeneric Hybrid Method

Hexaploid triticale is an important forage crop and a promising energy plant. Some forms were previously reported for developing the hexaploid triticale, such as crossing tetraploid wheat or hexaploid wheat with rye, crossing hexaploid triticale and/or hexaploid wheat with octoploid triticale, and spontaneously appearing in the selfed progenies of octoploid triticale. In the present study, we developed an effective method for production of diverse types of hexaploid triticale via wheat—rye—Psathyrostachys huashanica trigeneric hybrid. Genomic in situ hybridization (GISH) and fluorescence in situ hybridization (FISH) karyotyping revealed that D genome chromosomes were completely eliminated and the whole A, B, and R genome chromosomes were retained in three lines. More interestingly, the composite genome of the line K14-489-2 consisted of complete A and B genomes and chromosomes 1D, 2R, 3R, 4R, 5R, 6R, and 7R, that of line K14-491-2 was 12 A-genome (1A-6A), 14 B-genome (1B-7B), 12 R-genome (1R-3R, 5R-7R), and chromosomes 1D and 3D, and that of the line K14-547-1 had 26A/B and 14R chromosomes, plus one pair of centric 6BL/2DS translocations. This finding implies that some of D genome chromosomes can be spontaneously and stably incorporated into the hexaploid triticale. Additionally, a variety of high-molecular-weight glutenin subunits (HMW-GS) compositions were detected in the six hexaploid triticale lines, respectively. Besides, compared with its recurrent triticale parent Zhongsi828, these lines showed high level of resistance to stripe rust (Puccinia striiformis f. sp. tritici, Pst) pathogens prevalent in China, including V26/Gui 22. These new hexaploid triticales not only enhanced diversification of triticale but also could be utilized as valuable germplasm for wheat improvement.

Chromosomal Behavior during Meiosis in the Progeny of Triticum timopheevii × Hexaploid Wild Oat

The meiotic behavior of pollen mother cells (PMCs) of the F2 and F3 progeny from Triticum timopheevii × hexaploid wild oat was investigated by cytological analysis and sequential C-banding-genomic in situ hybridization (GISH) in the present study. A cytological analysis showed that the chromosome numbers of the F2 and F3 progeny ranged from 28 to 41. A large number of univalents, lagging chromosomes, chromosome bridges and micronuclei were found at the metaphase I, anaphase I, anaphase II and tetrad stages in the F2 and F3 progeny. The averages of univalents were 3.50 and 2.73 per cell, and those of lagging chromosomes were 3.37 and 1.87 in the F2 and F3 progeny, respectively. The PMC meiotic indices of the F2 and F3 progeny were 12.22 and 20.34, respectively, indicating considerable genetic instability. A sequential C-banding-GISH analysis revealed that some chromosomes and fragments from the hexaploid wild oat were detected at metaphase I and anaphase I in the progeny, showing that the progeny were of true intergeneric hybrid origin. The alien chromosomes 6A, 7A, 3C and 2D were lost during transmission from F2 to F3. In addition, partial T. timopheevii chromosomes appeared in the form of univalents or lagging chromosomes, which might result from large genome differences between the parents, and the wild oat chromosome introgression interfered with the wheat homologues' normally pairing.