Limonium homoploid and heteroploid intra- and interspecific crosses unveil seed anomalies and neopolyploidy related to sexual and/or apomictic reproduction (original) (raw)
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Euphytica, 2010
New tri-species hybrids (GOS) in the genus Pennisetum involving the cultivated species pearl millet (P. glaucum L.) and two wild species, viz. P. squamulatum Fresen and P. orientale L. C. Rich, are reported. Six hybrid plants were recovered after crossing a backcross hybrid (2n = 3x = 23, GGO) between P. glaucum (2n = 2x = 14, GG) and P. orientale (2n = 2x = 18, OO) with F1s (2n = 6x = 42, GGSSSS) between P. glaucum (2n = 4x = 28, GGGG) and P. squamulatum (2n = 8x = 56, SSSSSSSS). The hybrids were perennial, morphologically intermediate to their parents, and represented characters from the three contributing species. The hybrids contained 2n = 44 chromosomes (GGGSSO) representing 21, 14 and nine chromosomes from P. glaucum, P. squamulatum and P. orientale, respectively. Meiotic and flow-cytometric analysis suggested origin of these hybrids from unreduced female and reduced male gametes. Average chromosome configuration (8.42I + 14.32II + 1.62III + 0.52IV) at Meiosis showed limited inter-genomic pairing indicating absence of significant homology between the three genomes. The hybrids were male sterile (except one) and highly aposporous. P. orientale was identified to induce apospory in hybrid background with P. glaucum at diploid and above levels, though it was quantitatively affected by genomic doses from sexual parent. A case of inducible and recurrent apospory is presented whereby a transition from Polygonum-type sexual embryo-sacs to Panicum-type aposporous embryo-sacs was observed in diploid interspecific hybrids. Results supported independent origin and partitioning of the three apomixis-components (apomeiosis, parthenogenesis, and functional endosperm development), reported for the first time in Pennisetum. Potential utilization of GOS hybrids in understanding genome interactions involved in complex traits, such as perenniality and apomixis, is discussed.
Heredity, 2004
According to previous cytological evidence, the hemisexual dog-rose species, Rosa sect. Caninae, transmit only seven chromosomes (derived from seven bivalents) through their pollen grains, whereas egg cells contain 21, 28 or 35 chromosomes (derived from seven bivalents and 14, 21 or 28 univalents) depending on ploidy level. Two sets of reciprocal pairwise interspecific crosses involving the pentaploid species pair R. dumalis and R. rubiginosa, and the pentaploid/tetraploid species pair R. sherardii and R. villosa, were analysed for 13 and 12 microsatellite DNA loci, respectively. Single loci were represented by a maximum of three simultaneously occurring alleles in R. villosa, and four alleles in the other three parental plants. In the experimentally derived offspring, the theoretical maximum of five alleles was found for only one locus in the pentaploid progenies. Microsatellite DNA allele composition was identical with that of the maternal parent in 10 offspring plants, which were probably derived through apomixis. Almost all microsatellite DNA alleles were shared with the maternal parent also in the remaining offspring, but 1-4 alleles shared only with the paternal parent, indicating sexual seed formation. Analysis of quantitative peak differences allowed a tentative estimation of allelic configuration in the individual plants, and suggested that bivalent formation preferentially takes place between chromosomes that consistently share the same microsatellite alleles and therefore appear to be highly homologous. Moreover, alleles that were shared between the species in each cross combination comparatively often appear to reside on the bivalent-forming chromosomes, whereas species-specific alleles instead occur comparatively often on the univalent-forming chromosomes and are therefore inherited through the maternal parent only. Recombination then takes place between very similar genomes also in interspecific crosses, resulting in a reproduction system that is essentially a mixture between apomixis and selfing.
Cytogenetics of Semi-Fertile Triploid and Aneuploid Intergeneric Vine Cacti Hybrids
Journal of Heredity, 2005
Crosses between the diploid Hylocereus polyrhizus, as the female parent, and the tetraploid Selenicereus megalanthus, as the male parent, yielded triploid and aneuploid hybrids. The fruits of these hybrids combined the attractive appearance of Hylocereus fruits with the delicious taste of S. megalanthus fruits. The aim of this work was to assess the fertility and breeding potential of the triploid and aneuploid hybrids with a view to developing an improved vine cactus crop. Pollen mother cells at metaphase I revealed univalents, bivalents, trivalents, and occasionally quadrivalents. Chromosome distribution at anaphase I revealed different classes of chromosome segregation as well as lagging chromosomes. At metaphase II, parallel and tripolar spindles were observed. The occurrence of triads was frequent, whereas dyads were rarely observed. Pollen stainability varied among the clones studied ranging from 9.8% to 18.6%. The diameters of the stained pollen grains varied widely, probably as a result of the number of chromosomes. Despite the allotriploid origin of our hybrids, functional female and male gametes were produced in considerable proportions, most likely as a result of balanced chromosome segregation. The triploid and aneuploid clones studied yielded viable seeds whose number per fruit was strongly dependent on the pollen donor.
POLYPLOIDY IN PLANT BREEDING, 2019
Plant breeding is being playing significant role for the improvement of the characteristics of the plants required for the development of the new variety successfully and economically. Hybridization is being utilizing for creating genetic variation for the improvement of the crop. Polyploidy is now an interesting field of study to reveal the evolution of crop plants and utilizing their variability in the field of crop breeding. The most important use of polyploidy is to overcome or remove the sterility of hybrids which are borne by hybridization or distant cross, inter specific or inter-generic. Polyploidy is divided in to two major groups; autopolyploidy and allopolyploidy which lead to polyploidy where multiple sets of chromosomes occur in the nucleus. Both autopolyploidy and allopolyploidy mostly occur in plants, and can occur naturally or under the influence of chemicals. But autopolyploidy refers to a type of polyploidy where the chromosome complement consists of more than two copies of homologous chromosomes, while allopolyploidy refers to a type of polyploidy where the chromosome complement consists of more than two copies of chromosomes derived from different species. The genetics of polyploids depends essentially on the pairing properties of the multiple chromosomes in meiosis. If the multiple copies of a genome are sufficiently dissimilar from each other, they tend to pair among themselves and maintain the genetic variation within each genome. If the multiple copies of a genome are similar to each other, then all copies are free to pair and recombine among themselves. The application of polyploidy in plant breeding broadens the potential base of variability by increasing the number of genes that which can mutate, on other hand adds genetic diversity on variability in plant kingdom and also deleterious recessive mutations may be covered up by their dominant alleles to a greater extent in polyploidy. The application of polyploid in crop improvement is used as utilization of a bridge species-transfer of genes from wild to cultivated species. New crop species created through successful synthetic allopolyploidy. Polyploids are also have some limitations in which autopolyploids with larger sizes are accompanied with water and faced low dry matter content and show sterility with poor seed set. Also due to the complex segregation in autotetraploids, progress under selection is slow. Triploid cannot be maintained except through clonal propagation and effect of autopolyploidy cannot be easily predicted.
Annals of …, 2007
Aims Gametophytic apomixis is regularly associated with polyploidy. It has been hypothesized that apomixis is not present in diploid plants because of a pleiotropic lethal effect associated with monoploid gametes. Rare apomictic triploid plants for Paspalum notatum and P. simplex, which usually have sexual diploid and apomictic tetraploid races, were acquired. These triploids normally produce male gametes through meiosis with a range of chromosome numbers from monoploid (n ¼ 10) to diploid (n ¼ 20). The patterns of apomixis transmission in Paspalum were investigated in relation to the ploidy levels of gametes. † Methods Intraspecific crosses were made between sexual diploid, triploid and tetraploid plants as female parents and apomictic triploid plants as male parents. Apomictic progeny were identified by using molecular markers completely linked to apomixis and the analysis of mature embryo sacs. The chromosome number of the male gamete was inferred from chromosome counts of each progeny. † Key Results The chromosome numbers of the progeny indicated that the chromosome input of male gametes depended on the chromosome number of the female gamete. The apomictic trait was not transmitted through monoploid gametes, at least when the progeny was diploid. Diploid or near-diploid gametes transmitted apomixis at very low rates. † Conclusions Since male monoploid gametes usually failed to form polyploid progenies, for example triploids after 4x  3x crosses, it was not possible to determine whether apomixis could segregate in polyploid progenies by means of monoploid gametes.
Chromosomal and embryological analyses in sexual x apomictic hybrids ofPanicum maximum Jacq
Theoretical and Applied Genetics, 1980
Cytological analyses in series of crosses between 7 sexual pistillate and 8 apomictic staminate parents of species Panicum nzaximunz (Gramineae) are reported. Although these 15 progenitors were tetraploid (2n = 32), 2 dihaploids (2n = 16), 45 hexaploids (2n = 48) and 5 octoploids (2n = 64) were observed among 333 progeny plants. The role of unreduced gametes as the originators of polyploidy is discussed in relation to the so-called 'elements of apomixis'. The 2 dihaploids appeared to be sexual while the hexaploids and octoploids were all apomictic. At the tetraploid level sexual and apomictic hybrids segregated in a, ratio close to 1: 1. These results were then compared to those already obtained from studies on other tropical grasses and indicate a simple genetic determinism for gametophytic apomixis.
2010
Sexual polyploids were induced in diploid (2n = 2x = 24) interspecific F1 hybrids of Longiflorum 9 Asiatic (LA) and Oriental 9 Asiatic (OA) Lilium hybrids by backcrossing to Asiatic (AA) parents as well as by sib-mating of the F1 LA hybrids. A majority of the BC1 progenies were triploid and the progenies from sib-mating were tetraploid or near tetraploids. Genomic in situ hybridization (GISH) technique was applied to assess the intergenomic recombination in the BC1 populations of LA and OA hybrids obtained after unilateral sexual polyploidization. A total of 63 LA (LA 9 AA and AA 9 LA) and 53 OA hybrids were analysed. LA hybrids were originated through the functioning of 2n gametes either as 2n eggs or 2n pollen while those of OA hybrids originated through functional 2n pollen of diploid OA genotype. In both type of crosses, a majority of the progenies had originated through First Division Restitution (FDR) mechanism of functional 2n gamete either with or without a cross over. However, there were nine LA-and four OA-genotypes where Indeterminate Meiotic Restitution (IMR) was the mechanism of 2n gamete formation. Based on GISH, total amount of introgression of Longiflorum and Oriental genome into Asiatic genome was determined. Most of the BC progenies exhibited recombination and the amount of recombination was higher in LA hybrids as compared to OA hybrids. Intergenomic recombination was also determined cytologically in the 16 plants of sib-mated LA hybrids where both parents had contributed 2n gametes. Based on these results the nature of interspecific lily hybrids obtained from uni-and bilateral sexual polyploidization leading to allotriploid and allotetraploid formation is discussed in the context of introgression and intergenomic recombination.
The Significance of Polyploidy for Bulbous Ornamentals: A Molecular Cytogenetic Assessment
Floriculture and Ornamental Biotechnology, 2012
Most of the bulbous crops, viz., Crocus, Narcissus, Tulipa, Alstroemeria and Lilium that are commercially important, share certain common characteristics. The present day cultivars are all derived from hybrids between distantly related species, and in almost all cases spontaneous polyploidization has played a prominent role and there is a tendency to replace diploids by polyploid cultivars. Molecular cytogenetic techniques such as genomic in situ hybridization (GISH) and fluorescence in situ hybridization (FISH), along with other techniques, have greatly facilitated our understanding of the modes of origins of polyploids. Because the bulbous crops generally have large chromosomes, the parental genomes, individual chromosomes, as well as intergenomic recombinant chromosomes, can be accurately identified in the interspecific hybrids and their backcross progenies. This enables an assessment of the potential genetic variation that might occur in the progenies as well as the extent of introgression. Although the superiority of polyploids as compared to their diploid parents is beyond doubt, the actual explanation for their superiority is still elusive. Of the several explanations, chromosome dosage, optimal amounts of 4C DNA values of the complements, heterozygosity and favourable gene interactions transmitted by the 2n gametes to polyploid progenies are some of the factors that might be considered at present. Undoubtedly, more studies on the bulbous ornamental crops using molecular techniques might be rewarding.
Euphytica, 2007
The analytic-synthetic scheme makes use of haploidization and 2n gametes-mediated sexual polyploidization to incorporate genetic diversity from wild related species in potato breeding. Whereas 2n pollen can be directly screened by microscopy, 2n eggs are routinely screened indirectly by interploid crosses, a timeconsuming and inaccurate technique. In five haploid tbr · wild diploid species families with variability for agronomic characters, 2n eggs were screened indirectly to incorporate this germplasm into a useful form and directly by microscopy to establish the feasibility of this approach. For the indirect screening, at least 15 flowers of each of 49 genotypes/family were crossed with a commercial cultivar. Eighty-five fruits were produced; only 15 of them had seeds (1-25). Chromosome numbers were determined in a random sample of five seeds/ fruit, resulting diploid in two genotypic combinations and tetraploid in another two. For the direct screening, eight combinations of staining and destaining (times and concentrations) were evaluated in detached ovules to adjust a clarification technique. The best combination was one day of staining and one day of destaining in 0.5 % acetic acid. In an indirectly detected diplogynoid, the average diameters of the central cell nuclei (CCN) and nucleoli (CCNu) were, respectively, 9.3 l and 3.4 l. Gametophytes with diametres 1.26 times the average were considered 2n. By crosses, eleven seeds were obtained in one fruit of this clone whereas the 2n egg frequency determined by microscopy was 7%. The direct technique is easy to carry out once the eye is trained and its results better reflect actual 2n gamete frequencies.