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Abstract [Objective] Most intersectional hybrids in Paeonia are triploids and generally sterile, producing a small number of hybrid offspring. Observing the meiotic chromosome behaviors of ‘Bartzella’, an intersectional hybrid with high ornamental value and several hybrid offspring, can provide insight into the formation mechanism of its low fertility. [Methods] The study utilized the anthers of ‘Bartzella’ as materials to observe the meiotic chromosome behaviors of pollen mother cells (PMCs) through the squash method. [Results] (1) In metaphase Ⅰ, a significant number of univalents were formed in ‘Bartzella’ PMCs. In anaphase Ⅰ, various types of chromosomal aneuploid segregation were observed, accounting for up to 89.13%. (2) During the first meiotic division, chromosome bridges and fragments were found in 27.20% of the PMCs; during the second meiotic division, this percentage was increased to 47.68%. (3) In metaphase Ⅱ, spindle positioning abnormalities were relatively common, with fused spindles accounting for 27.06% and tripolar spindles accounting for 12.84%. The meiotic products included up to 72.41% of dyads and 13.43% of triads, which could generate unreduced gametes accounting for about 67%. [Conclusion] Chromosome aneuploidy segregation and loss of chromosome segments during meiosis may be the primary causes of the high sterility of ‘Bartzella’. Fused spindles, tripolar spindles, and abnormal cytokinesis at the end of second meiotic division may result in the production of unreduced gametes. The significant number of unreduced gametes might give ‘Bartzella’ the potential polyploid breeding. However, interploidy hybridization barriers could restrict its hybrid affinity.

There are thousands of Narcissus cultivars, however; their genome compositions are not so clear, except that their ploidy levels are extensively investigated. The present study analyzed eight popular cultivars using GISH or/and FISH. The present results clearly revealed their genome compositions: 'Bridal Crown' was diploid (2n = 2x = 17 = 10 + 7 = AE) rather than aneuploid, 'Jinzhanyintai' was autotriploid (2n = 3x = 30 = 10 + 10 + 10 = AAA) rather than allotetraploid or hexaploid, 'Tête-à-Tête' was allotriploid (2n = 3x = 24 + B = 10 + 7 + 7 + B = AEE), 'Cultivar X' was also allotriploid (2n = 3x = 24 = 10 + 7 + 7 = AEX), and 'Dutch Master', 'Replete' and 'Queen's Day' were all autotetraploid (2n = 4x = 28 = 7 + 7 + 7 + 7 = EEEE). Together with other reports, we concluded that 'Tête-à-Tête' contained one genome of Narcissus tazetta, one genome of Narcissus cyclamineus, and one genome of Narcissus pseudonarcissus, and that 'Pink Parasol' was aneu-autotetraploid (2n = 4x + 2 = 30 = 7 + 7 + 7 + 7 + 2 = EEEE+2) rather allotetraploid (2n = 4x = 10 + 10 + 5 + 5 = CCDD). Based on the cultivar's genome composition and origin, it is concluded that distant hybridization, sexual polyploidization and chromosome doubling play different roles in breeding modern Narcissus cultivars. [ABSTRACT FROM AUTHOR]

Key message: Epidendrum produces 2n gametes with high frequency. This paper is the first to report on multiple pathways for forming 2n gametes, meiotic defeats, and pre-meiotic chromosome doubling. Unreduced 2n reproductive cells are predominantly involved in pathways that lead to polyploid plants. Although one of the most common pathways for inducing 2n gametes is through meiotic defects, a small set of isolated species alternatively generates 2n gametes from tetraploid pollen mother cells in the pre-meiotic phase. Hence, determining the mechanisms underlying 2n gamete formation is critical to improving breeding programmes and understanding plant evolution. We investigated sporads to reveal the pathway(s) accounting for the formation and frequencies of 2n gametes in wild species and interspecific hybrids in the genus Epidendrum. We investigated different types of sporads with varying frequencies, sizes, and viability in the wild species and hybrids of the genus Epidendrum. Large tetrad-estimated pre-meiotic chromosome doubling was observed in wild species. The Epidendrum is unique in that it forms 2n pollens via two pathways, namely, meiotic defects and pre-meiotic chromosome doubling. These two pathways of 2n pollen formation could influence the high diversity generation of polyploidy with different degrees of heterozygosity and genetic backgrounds in the genus Epidendrum. Therefore, these findings are proposed to influence polyploid breeding of Epidendrum via 2n pollen, helping us understand evolution and speciation via unreduced 2n gamete formation in Orchidaceae. [ABSTRACT FROM AUTHOR]

Polyploid plants, an important source for the selection of ornamental plants for their advantages of faster growth, higher yields, and stronger adaptability to an adverse environment, play an essential role in the development of economic plants for agricultural stress. The methodology has been improved to decrease blindness and increase the efficiency of ornamental plants’ polyploid breeding in the long term. The progress of research on ornamental plants related to natural polyploidy, chromosome doubling, the 2n gametes pathway, and plant ploidy identification are reviewed in this paper. The main routes in polyploid breeding are chromosome doubling and sexual hybridization. Screening of suitable induction methods and plant material should be enhanced in chromosome doubling to improve induction efficiency. Regarding polyploid breeding, the utilization and research on 2n gametes produced by natural conditions or artificial induction should be strengthened to shorten the breeding years. Therefore, further research should strengthen the combination of chromosome doubling and sexual hybridization to improve breeding efficiency and strengthen the research and application of polyploid plants. This thesis review provides some reference value for polyploid breeding in ornamental plants.

Pollen characteristics are very important for Iris interspecific hybridisation. In this study, the pollen viability and male meiosis were studied in yellow-flowered Iris dichotoma (Y2), I. domestica (S3) and their hybrids F1, F2 and BC1 (BC1-Y and BC1-S). The BC1-Y hybrids showed higher pollen viability than that of F1, F2 and BC1-S hybrids, which were between I. dichotoma (26.1%) and I. domestica (35.1%). Two sterile hybrids, F2-1 and BC1-S-1, exhibited more meiotic abnormalities (57.3% and 58.7%) than other individuals. During the first meiotic division, a diffuse diplotene stage was observed for the first time in the genus Iris. The meiotic abnormalities included non-congressed chromosomes, chromosome bridges, lagging chromosomes, unequal division, abnormally oriented spindle fibres, nonsynchronous division and polyad, and resulted in reduced pollen fertility. The relatively high frequency of 2n pollen grains was found in hybrids of BC1-Y-2, BC1-Y-1, BC1-S-2, BC1-S-3 and BC1-S-4. Our research provides a new resource for meiotic behaviour and pollen fertility of the genus Iris.

Lantana camara is an important plant for the environmental horticultural industry, yet it can be invasive, cross-pollinating with native lantana and dispersing fruit (and seeds) to natural and agricultural lands. Identification and development of sterile cultivars is much needed to meet industry and consumer needs for noninvasive plant materials. Previously we evaluated the male fertility of 32 L. camara cultivars/breeding lines at five ploidy levels. This study was to assess their female fertility and understand the relationship between female fertility and ploidy level and the production of unreduced female gametes (UFGs) in L. camara. These cultivars/breeding lines significantly varied in percent fruiting plants (6.3% to 100.0%), percent fruiting peduncles (0.3% to 98.8%), fruit per peduncle (0.003 to 7.173), seed germination (0% to 57.1%), and female fertility index (0.003 to 2.998). Certain diploids (e.g., ‘Denholm White’) were highly female-sterile. Eleven of the 13 triploids evaluated were UFG-producing and rather fertile. The two non-UFG-producing triploids had the female fertility index of 0.005, thus most sterile. Tetraploids, especially those producing UFGs, were prolific fruit producers. These results show that ploidy level and UFG production play a significant role in determining fruit (seed) production capacity and female fertility of L. camara. None of the commercial triploid cultivars evaluated reached desirable levels of male and female sterility, indicating a strong need to develop new lantana cultivars that are male- and female-sterile. Our results suggest that production and selection of triploids can be effective to sterilize L. camara, but it is imperative to select diploids and tetraploids that do not produce UFGs as the breeding parents.

High compatibility in interspecific crosses among species of Saccharum with peculiar chromosome transmissions in the progeny is well documented. It depends upon the species combination used in the interspecific crosses. Though 2n + n transmission is common in Saccharum officinarum x S. spontaneum, which led to the success of the first man made interspecific commercial hybrid Co 205, it is an uncommon phenomenon with commercial cultivar x S. spontaneum. Recently, 2n+n transmission with female restitution in two hybrids from the crosses of Co 89029 (2n=110) x S. spontaneum (2n =88) and Co 89029 (2n=110) x S. spontaneum (2n = 112) has been identified. These hybrids, 04-2153 with 2n=153 and 04-244, 2n=166 were evaluated for their agronomic characters. Improvement over the female parent was observed for number of millable canes (74.3%), plant height (15.0 % ), cane yield (7.37 %), dry matter production (67.14%), fibre (59.62 %) and pollen fertility (97.16 %) in the hybrid 04-2153 while the hybrid 04-244 had shown considerable improvement over the female parent for number of millable canes (49.85 %), cane yield (25.59 %), pollen fertility (46.83%), dry matter production (34.27) and fibre content (46.15%). Performance of these hybrids and their utilisation in commercial breeding programme are discussed.

Pollen characteristics are very important for Iris interspecific hybridisation. In this study, the pollen viability and male meiosis were studied in yellow-flowered Iris dichotoma (Y2), I. domestica (S3) and their hybrids F1, F2 and BC1 (BC1-Y and BC1-S). The BC1-Y hybrids showed higher pollen viability than that of F1, F2 and BC1-S hybrids, which were between I. dichotoma (26.1%) and I. domestica (35.1%). Two sterile hybrids, F2-1 and BC1-S-1, exhibited more meiotic abnormalities (57.3% and 58.7%) than other individuals. During the first meiotic division, a diffuse diplotene stage was observed for the first time in the genus Iris. The meiotic abnormalities included non-congressed chromosomes, chromosome bridges, lagging chromosomes, unequal division, abnormally oriented spindle fibres, nonsynchronous division and polyad, and resulted in reduced pollen fertility. The relatively high frequency of 2n pollen grains was found in hybrids of BC1-Y-2, BC1-Y-1, BC1-S-2, BC1-S-3 and BC1-S-4. Our research provides a new resource for meiotic behaviour and pollen fertility of the genus Iris. [ABSTRACT FROM AUTHOR]

Polyploidy plays an important role in crop improvement. Polyploid plants, particularly those produced through unreduced gametes (2n gametes), show increased organ size, improved buffering capacity for deleterious mutations, and enhanced heterozygosity and heterosis. Induced polyploidy has been widely used for improving floriculture crops, however, there are few reported sexual polyploid plants in the floriculture industry. This study evaluated nine cultivars of Cymbidium Swartz and discovered that 2n male gametes occurred in this important orchid. Depending on cultivars, 2n male gamete formation frequencies varied from 0.15 to 4.03%. Interspecific hybrids generally produced more 2n male gametes than traditional cultivars. To generate sexual polyploid plants, seven pairs of crosses were made, which produced five triploid and two tetraploid hybrids. Two triploid hybrids were evaluated for in vitro regeneration and growth characteristics. Compared to the diploid parents, the triploids were more easily regenerated through rhizomes or protocorms, and regenerated plants had improved survival rates after transplanting to the greenhouse. Furthermore, the sexual polyploid plants had more compact growth style, produced fragrant flowers, and demonstrated heterosis in plant growth. Through this study, a reliable protocol for selection of appropriate parents for 2n gamete production, ploidy level evaluation, in vitro culture of polyploid progenies, and development of new polyploid cultivars was established. Our study with Cymbidium suggests that the use of 2n gametes is a viable approach for improving floriculture crops.

Lantana camara is an important plant for the environmental horticultural industry, yet it can be invasive, cross-pollinating with native lantana and dispersing fruit (and seeds) to natural and agricultural lands. Identification and development of sterile cultivars is much needed to meet industry and consumer needs for noninvasive plant materials. Previously we evaluated the male fertility of 32 L. camara cultivars/breeding lines at five ploidy levels. This study was to assess their female fertility and understand the relationship between female fertility and ploidy level and the production of unreduced female gametes (UFGs) in L. camara. These cultivars/breeding lines significantly varied in percent fruiting plants (6.3% to 100.0%), percent fruiting peduncles (0.3% to 98.8%), fruit per peduncle (0.003 to 7.173), seed germination (0% to 57.1%), and female fertility index (0.003 to 2.998). Certain diploids (e.g., 'Denholm White') were highly female- sterile. Eleven of the 13 triploids evaluated were UFG-producing and rather fertile. The two non-UFG-producing triploids had the female fertility index of 0.005, thus most sterile. Tetraploids, especially those producing UFGs, were prolific fruit producers. These results show that ploidy level and UFG production play a significant role in determining fruit (seed) production capacity and female fertility of L. camara. None of the commercial triploid cultivars evaluated reached desirable levels of male and female sterility, indicating a strong need to develop new lantana cultivars that are male- and female-sterile. Our results suggest that production and selection of triploids can be effective to sterilize L. camara, but it is imperative to select diploids and tetraploids that do not produce UFGs as the breeding parents. [ABSTRACT FROM AUTHOR]

The gene flow mediated by unreduced gametes between diploid and tetraploid plants of the Medicagosativa-coerulea-falcata complex is pivotal for alfalfa breeding. Sexually tetraploidized hybrids could represent the best way to exploit progressive heterosis simultaneously derived from gene diversity, heterozygosity, and polyploidy. Moreover, unreduced gametes combined with parthenogenesis (i.e., apomixis) would enable the cloning of plants through seeds, providing a unique opportunity for the selection of superior genotypes with permanently fixed heterosis. This reproductive strategy has never been detected in the genus Medicago, but features of apomixis, such as restitutional apomeiosis and haploid parthenogenesis, have been reported. By means of an original case study, we demonstrated that sexually tetraploidized plants maintain apomeiosis, but this trait is developmentally independent from parthenogenesis. Alfalfa meiotic mutants producing unreduced egg cells revealed a null or very low capacity for parthenogenesis. The overall achievements reached so far are reviewed and discussed along with the efforts and strategies made for exploiting reproductive mutants that express apomictic elements in alfalfa breeding programs. Although several studies have investigated the cytological mechanisms responsible for 2n gamete formation and the inheritance of this trait, only a very small number of molecular markers and candidate genes putatively linked to unreduced gamete formation have been identified. Furthermore, this scenario has remained almost unchanged over the last two decades. Here, we propose a reverse genetics approach, by exploiting the genomic and transcriptomic resources available in alfalfa. Through a comparison with 9 proteins belonging to Arabidopsis thaliana known for their involvement in 2n gamete production, we identified 47 orthologous genes and evaluated their expression in several tissues, paving the way for novel candidate gene characterization studies. An overall view on strategies suitable to fill the gap between well-established meiotic mutants and next-generation genomic resources is presented and discussed.

Wild potato relatives are important sources of novel genes useful for potato improvement. Since most wild potato species are diploid and most cultivars are tetraploid, it is typically necessary to employ ploidy manipulations to access wild potato germplasm. A common strategy is unilateral sexual polyploidization (USP), in which a tetraploid cultivated clone is crossed with a diploid that produces 2n gametes. The diploid parent may be a wild plant selected for a trait of interest. Alternatively, the wild plant may be crossed to a cultivated diploid and, after selection, the diploid hybrid is then crossed to the tetraploid parent. This study was designed to compare these two strategies for the introgression of common scab resistance from wild diploid Solanum chacoense (chc) into cultivated potato. Progeny were evaluated in naturally scab-infested soil in Maine and Michigan. There were no differences between introgression methods for tuber surface area covered by scab. Scab lesions were significantly more severe when a hybrid was used as the diploid parent, but this difference is likely not large enough to be important in a breeding program. Reciprocal cross differences were not significant. However, location x clone interactions were detected for both surface area and lesion type. This study revealed that, while hybridization strategy did not play a major role in developing this scab resistant germplasm, it is critical to consider production environment when screening for resistance. [ABSTRACT FROM AUTHOR]

The Alchornea triplinervia specie belongs to the Euphorbiaceae family, one of the main families of the Brazilian flora. In order to contribute to a better understanding of the specie, a counting of chromosome number and the microsporogenesis analysis of A. triplinervia were done. The inflorescences were collected in the municipalities of Paranavaí and Diamante do Norte, State of Paraná, Brazil, and the slides were prepared by squashing technique and staining with 1% acetic carmine. The analysis were performed using an optical microscope and showed a chromosome number for the specie equal to 2n=8x=72. Irregularities in the chromosome segregation process were the main meiotic abnormalities, presenting typical polyploid behavior. Other irregularities were observed; however, at low frequency without compromising the pollen grain formation of the analyzed plants.A espécie Alchornea triplinervia pertence à família Euphorbiaceae, uma das principais famílias da flora brasileira. Visando a contribuir para um melhor entendimento da espécie, foi realizada a contagem do número de cromossomos e a análise da microsporogênese de A. triplinervia. As Inflorescências foram coletadas nos Municípios de Paranavaí e Diamante do Norte, no Estado do Paraná, Brasil, sendo as lâminas preparadas pela técnica de esmagamento e coradas com carmim acético 1%. As análises foram realizadas ao microscópio óptico, revelando um número cromossômico para a espécie igual a 2n=8x=72. Irregularidades no processo de segregação dos cromossomos foram as principais anormalidades meióticas, mostrando comportamento típico de poliploides. Outras irregularidades foram observadas, porém, em baixa frequência, não comprometendo a formação dos grãos de pólen das plantas analisadas.

Sexual polyploidization has both a theoretical as well as an applied significance. Morphological screening for large pollen grains and shape of pollen produced by the individual, cytological investigation of hybrid progeny, and unbalanced separation of chromosomes at anaphase I in pollen mother cells were used to detect the gametes with somatic chromosome number in Fuchsia. The interspecific hybrids of F. fulgens (sect. Ellobium) × F. magellanica (sect. Quelusia), F. fulgens (sect. Ellobium) × F. splendens (sect. Ellobium), and F. triphylla (sect. Fuchsia) × F. splendens (sect. Ellobium) produced at the University of Auckland, New Zealand, showed both large and normal pollen grains in the same anther indicating the presence of unreduced gametes. Cytological investigation carried out on the hybrid progeny of F. fulgens (diploid, 2n=22, sect. Ellobium) × F. magellanica (tetraploid, 2n=44, sect. Quelusia) and F. triphylla (diploid, sect. Fuchsia) × F. arborescens (diploid, sect. Schufia) revealed unexpected chromosome numbers of 2n=44 and 2n=33, respectively. In general, the hybrids showed low fertility caused by genetically unbalanced gametes resulted from random disjunction of chromosomes at anaphase I. Studies on meiosis together with the presence of different shapes and sizes of pollen grains in Fuchsia proved indirectly that unreduced gametes are the products of first division meiotic nuclear restitution. These unreduced gametes were viable irrespective of pollen shape, their predominance in the hybrids, nuclear DNA amount and species phylogenetic position.

Almost 90% of species of the genus Passiflora are native to the American continent, with high commercial value due to the fact that some species are used for human food while others have ornamental and medical qualities. Passiflora serrato-digitata is one of the species that integrates the Paraná Agronomic Institute germoplasm bank at its experimental base in Londrina, PR, Brazil. Collected flower buds were fixed in ethanol/acetic acid (3:1 v/v) for 24h, transferred to 70% alcohol and stored under refrigeration. Slides were prepared by the squashing technique and stained with 1.0% propionic carmine; they were analyzed under an optic microscope. Irregularities in the chromosome segregation process of P. serrato-digitata have been verified by meiotic behavior analysis. These comprised precocious migration to poles in metaphase I and II, non-oriented chromosomes in metaphase plate in metaphase I and II, laggard chromosomes in anaphase I and II towards the formation of micronucleus in telophase I and II, and microspores in tetrads. Chromosome stickiness was another irregularity reported in the Passiflora genus for the first time. These irregularities which also contributed to the formation of monads, dyads and triads, resulted in normal imbalanced 2n and 4n microspores. According to the observed Meiotic Index of 71.83%, this species is not meiotically stable.Cerca de 90% das espécies do gênero Passiflora são nativas das Américas, sendo que aproximadamente 200 espécies são nativas do Brasil. Possuem grande importância comercial, pois algumas espécies são utilizadas na alimentação humana, outras apresentam propriedades medicinais e ornamentais. A espécie Passiflora serrato-digitata faz parte do banco de germoplasma do Instituto Agronômico do Paraná - IAPAR, estação experimental de Londrina, PR. Botões florais colhidos foram fixados em etanol/ácido acético (3:1 v/v) por 24 horas, transferidos para álcool a 70% e acondicionado sob refrigeração. As lâminas foram preparadas pela técnica de esmagamento e coradas com carmim propiônico a 1,0% e observadas ao microscópio óptico. Por meio da análise do comportamento meiótico, foram verificadas irregularidades no processo de segregação dos cromossomos de P. serrato-digitata, tais como migração precoce para os pólos em metáfase I e II, cromossomos não orientados na placa equatorial em metáfase I e II, cromossomos retardatários em anáfase I e II, levando a formação de micronúcleo em telófases I e II e micrósporos em tétrades. Outra irregularidade observada foi aderência cromossômica, relatada pela primeira vez no gênero Passiflora, que também pode ter contribuído para a formação de mônades, díades, tríades, as quais foram observadas, resultando em micrósporos normais, desbalanceados, 2n e 4n. De acordo com o Índice Meiótico de 71,83% observado, essa espécie pode ser classificada como não estável meioticamente.

Endosperm Balance Number (EBN) is a genome-specific ploidy, which is not necessarily equivalent to the chromosome ploidy. The EBN is the ‘effective ploidy’ that determines crossability in Solanum species. It varies from 1 to 4 and the two Solanum species are crossable if they have the same EBN so that maternal to paternal ratio of EBN in the endosperm is 2:1. However, a number of significant exceptions to this rule have been observed in potato (Solanum tuberosum L.). EBNs have been experimentally assigned to a number of Solanum species after crosses with standard species whose EBN was arbitrarily established. Neither specific genes nor the molecular basis of EBN have been established in potato, but 2-3 unlinked loci with equal additive effects are known to determine the EBN in Solanum species. EBN acts as a powerful isolating mechanism in the sexual reproduction of Solanum species. EBN incompatibility played an important role in the speciation of polyploids from diploids, complementing the role of 2n gametes in the polyploidy evolution of potato species. EBN has great predictive value for planning interpsecific crosses in potato. EBN of a species can be modified through sexual or somatic polyploidization. This has facilitated the transfer of useful disease and pest resistance genes from 1 EBN and 2EBN wild species to 4EBN cultivated potatoes. Besides direct, indirect gene transfer through bridge species from otherwise incompatible Solanum species has been accomplished for improving cultivated potatoes. The concept, inheritance and role of EBN in speciation, and its prospects in potato varietal improvement are reviewed in this paper. The problems associated in transfer of useful traits from wild species to cultivated potatoes due to EBN barriers are also highlighted.

To integrate the gene pool of a wild species (primarily diploid) into a cultivated pool (primarily tetraploid), a crossing between a dihaploid cultivated rose and a hybrid of Rosa wichurana allowed to obtain interspecific diploid hybrids that produced 2n pollen grains. A return to a tetraploid level sought by breeders can then be considered using sexual polyploidization, obtained by crossing a tetraploid cultivated rose with these hybrids. Application of a high-temperature regime led to a small but significant increase in the percentage of 2n pollen grains in these hybrids of up to 4.6%. This result was obtained by applying high temperatures close to 32°C during the day to plants cultivated in a glasshouse during recurrent cycles of bloom. Crosses were made between an unreleased tetraploid hybrid tea rose, as a female, and the diploid hybrid that produces the most 2n pollen grains. Tetraploid (42.1%) and triploid (57.9%) offspring were obtained. The use of these 2n pollen grains of the first division restitution type should facilitate the introgression of complex traits of interest. [ABSTRACT FROM AUTHOR]

Background and Aims Dioscorea alata is a polyploid species with a ploidy level ranging from diploid (2n = 2x = 40) to tetraploid (2n = 4x = 80). Ploidy increase is correlated with better agronomic performance. The lack of knowledge about the origin of D. alata spontaneous polyploids (triploids and tetraploids) limits the efficiency of polyploid breeding. The objective of the present study was to use flow cytometry and microsatellite markers to understand the origin of D. alata polyploids. Methods Different progeny generated by intracytotype crosses (2x × 2x) and intercytotype crosses (2x × 4x and 3x × 2x) were analysed in order to understand endosperm incompatibility phenomena and gamete origins via the heterozygosity rate transmitted to progeny. Results This work shows that in a 2x × 2x cross, triploids with viable seeds are obtained only via a phenomenon of diploid female non-gametic reduction. The study of the transmission of heterozygosity made it possible to exclude polyspermy and polyembryony as the mechanisms at the origin of triploids. The fact that no seedlings were obtained by a 3x × 2x cross made it possible to confirm the sterility of triploid females. Flow cytometry analyses carried out on the endosperm of seeds resulting from 2x × 4x crosses revealed endosperm incompatibility phenomena. Conclusions The major conclusion is that the polyploids of D. alata would have appeared through the formation of unreduced gametes. The triploid pool would have been built and diversified through the formation of 2n gametes in diploid females as the result of the non-viability of seeds resulting from the formation of 2n sperm and of the non-viability of intercytotype crosses. The tetraploids would have appeared through bilateral sexual polyploidization via the union of two unreduced gametes due to the sterility of triploids. [ABSTRACT FROM AUTHOR]

670I.670II.671III.672IV.675V.680680References680 Summary: In the plant kingdom, events of whole genome duplication or polyploidization are generally believed to occur via alterations of the sexual reproduction process. Thereby, diploid pollen and eggs are formed that contain the somatic number of chromosomes rather than the gametophytic number. By participating in fertilization, these so‐called 2n gametes generate polyploid offspring and therefore constitute the basis for the establishment of polyploidy in plants. In addition, diplogamete formation, through meiotic restitution, is an essential component of apomixis and also serves as an important mechanism for the restoration of F1 hybrid fertility. Characterization of the cytological mechanisms and molecular factors underlying 2n gamete formation is therefore not only relevant for basic plant biology and evolution, but may also provide valuable cues for agricultural and biotechnological applications (e.g. reverse breeding, clonal seeds). Recent data have provided novel insights into the process of 2n pollen and egg formation and have revealed multiple means to the same end. Here, we summarize the cytological mechanisms and molecular regulatory networks underlying 2n gamete formation, and outline important mitotic and meiotic processes involved in the ectopic induction of sexual polyploidization. [ABSTRACT FROM AUTHOR]

We trialled a two-step method of producing allohexaploid Brassica with three genomes (A, B, and C) derived from pair-wise crossing among three allotetraploid Brassica species. In the first step, the three allotetraploid Brassica species ( Brassica juncea, AABB; Brassica napus, AACC; and Brassica carinata, BBCC) were intercrossed in pairs to produce unbalanced trigenomic hybrids: AABC, BBAC and CCAB. In the second step, these hybrids were crossed with the complementary allotetraploid parent, that is, AABC × BBCC ( B. carinata), BBAC × AACC ( B. napus) and CCAB × AABB ( B. juncea). We hypothesised that the unbalanced trigenomic hybrids would produce high levels of unreduced gametes with the same genome composition as the hybrid. These unreduced gametes would unite with reduced gametes from the complementary allotetraploids to form allohexaploid Brassica progeny (AABBCC). From 112 s generation interspecific progeny, two progeny were shown by locus-specific simple sequence repeat markers to be near-allohexaploids derived from an unreduced gamete from CCAB and a reduced gamete from B. juncea (AB). One of these plants was highly self-fertile, had 50 chromosomes, and inherited patterns of marker alleles (AABBCC) that were predicted from first division restitution at meiosis in the CCAB parent. The second near-allohexaploid had 60 chromosomes, was sterile, and inherited patterns of marker alleles that indicated second division restitution in the CCAB parent. Trigenomic hybrid Brassica produced by these methods will be valuable bridges to move alleles between allotetraploid species, and may contribute useful meiotic stability alleles to a future allohexaploid species. [ABSTRACT FROM AUTHOR]

The Alchornea triplinervia specie belongs to the Euphorbiaceae family, one of the main families of the Brazilian flora. In order to contribute to a better understanding of the specie, a counting of chromosome number and the microsporogenesis analysis of A. triplinervia were done. The inflorescences were collected in the municipalities of Paranavaí and Diamante do Norte, State of Paraná, Brazil, and the slides were prepared by squashing technique and staining with 1% acetic carmine. The analysis were performed using an optical microscope and showed a chromosome number for the specie equal to 2n=8x=72. Irregularities in the chromosome segregation process were the main meiotic abnormalities, presenting typical polyploid behavior. Other irregularities were observed; however, at low frequency without compromising the pollen grain formation of the analyzed plants. [ABSTRACT FROM AUTHOR]

Abstract: Parent–offspring regression has often been used for the estimation of breeding value and narrow-sense heritability in experimental populations, particularly for diploid species with regular disomic inheritance. With polysomic inheritance, estimates of heritability based on parent–offspring regression are expected to be systematically biased, particularly when intra- and inter-generation ploidy polymorphisms occur as a result of unusual megasporogenesis. Measuring the discrepancy between true and estimated heritability has important theoretical and practical implications for the genetic improvement of plantain and bananas. In this regard, formulas were developed to describe the relationships between parental and filial generations with different ploidy states and this information was used to estimate heritability for several traits of plantains and bananas. This approach may be extended to other polysomic species with similar meiotic behaviour and ploidy polymorphism. [Copyright &y& Elsevier]

Sexual polyploidization has both a theoretical as well as an applied significance. Morphological screening for large pollen grains and shape of pollen produced by the individual, cytological investigation of hybrid progeny, and unbalanced separation of chromosomes at anaphase I in pollen mother cells were used to detect the gametes with somatic chromosome number in Fuchsia. The interspecific hybrids of F. fulgens (sect. Ellobium) × F. magellanica (sect. Quelusia), F. fulgens (sect. Ellobium) × F. splendens (sect. Ellobium), and F. triphylla (sect. Fuchsia) × F. splendens (sect. Ellobium) produced at the University of Auckland, New Zealand, showed both large and normal pollen grains in the same anther indicating the presence of unreduced gametes. Cytological investigation carried out on the hybrid progeny of F. fulgens (diploid, 2n=22, sect. Ellobium) × F. magellanica (tetraploid, 2n=44, sect. Quelusia) and F. triphylla (diploid, sect. Fuchsia) × F. arborescens (diploid, sect. Schufia) revealed unexpected chromosome numbers of 2n=44 and 2n=33, respectively. In general, the hybrids showed low fertility caused by genetically unbalanced gametes resulted from random disjunction of chromosomes at anaphase I. Studies on meiosis together with the presence of different shapes and sizes of pollen grains in Fuchsia proved indirectly that unreduced gametes are the products of first division meiotic nuclear restitution. These unreduced gametes were viable irrespective of pollen shape, their predominance in the hybrids, nuclear DNA amount and species phylogenetic position. [ABSTRACT FROM AUTHOR]

Almost 90% of species of the genus Passiflora are native to the American continent, with high commercial value due to the fact that some species are used for human food while others have ornamental and medical qualities. Passiflora serrato-digitata is one of the species that integrates the Paraná Agronomic Institute germoplasm bank at its experimental base in Londrina, PR, Brazil. Collected flower buds were fixed in ethanol/acetic acid (3:1 v/v) for 24h, transferred to 70% alcohol and stored under refrigeration. Slides were prepared by the squashing technique and stained with 1.0% propionic carmine; they were analyzed under an optic microscope. Irregularities in the chromosome segregation process of P. serrato-digitata have been verified by meiotic behavior analysis. These comprised precocious migration to poles in metaphase I and II, non-oriented chromosomes in metaphase plate in metaphase I and II, laggard chromosomes in anaphase I and II towards the formation of micronucleus in telophase I and II, and microspores in tetrads. Chromosome stickiness was another irregularity reported in the Passiflora genus for the first time. These irregularities which also contributed to the formation of monads, dyads and triads, resulted in normal imbalanced 2n and 4n microspores. According to the observed Meiotic Index of 71.83%, this species is not meiotically stable. [ABSTRACT FROM AUTHOR]

Sexual polyploids were induced in diploid (2 n = 2 x = 24) interspecific F1 hybrids of Longiflorum × Asiatic (LA) and Oriental × 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 × AA and AA × LA) and 53 OA hybrids were analysed. LA hybrids were originated through the functioning of 2 n gametes either as 2 n eggs or 2 n pollen while those of OA hybrids originated through functional 2 n 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 2 n 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 2 n 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 2 n 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. [ABSTRACT FROM AUTHOR]

Ficus carica (2n = 26) is one of the oldest fruit trees of the Mediterranean basin. Recently there has been increasing interest in this species, in particular for questions related to germplasm such as genetic diversity and cultivar identification. This study was undertaken to gain more knowledge of F. carica cytogenetics and provide data useful for the characterization of its germplasm. Karyomorphological analysis and physical mapping of 18S-25S and 5S rRNA genes by the FISH technique contributed to defining the basic traits of the chromosome complement of F. carica. However, the most interesting result was the discovery of triploid (2n = 39) cytotypes of the cultivated common fig. This result demonstrates the importance of cytogenetic investigations in studies of fig germplasm and emphasizes the role of cross-fertilization as a source of variability not only in wild populations but also in cultivated forms. The results of pollen analysis suggest spontaneous sexual polyploidization as a possible origin of triploid cytotypes. Further studies are necessary to clarify the origin and effective spreading of polyploidy, the presence of other ploidy levels, and their distribution in wild and cultivated forms. [ABSTRACT FROM AUTHOR]

Background: Emeritus Campbell-Bascom Professor Stanley J. Peloquin was an internationally renowned plant geneticist and breeder who made exceptional contributions to the quantity, quality and sustainable supply of food for the world from his innovative and extensive scientific contributions. For five decades, Dr Peloquin merged basic research in plant reproduction, cytology, cytogenetics, genetics, potato (Solanum tuberosum) improvement and education at the University of Wisconsin-Madison. Successive advances across these five decades redefined scientific comprehension of reproductive variation, its genetic control, genetic effects, evolutionary impact and utility for breeding. In concert with the International Potato Center (CIP), he and others translated the advances into application, resulting in large benefits on food production worldwide, exemplifying the importance of integrated innovative university research and graduate education to meet domestic and international needs. [ABSTRACT FROM PUBLISHER]

Chromosomal recombination maps were constructed for three genomes of lily (Lilium) using GISH analyses. For this purpose, the backcross (BC) progenies of two diploid (2n = 2x = 24) interspecific hybrids of lily, viz. Longiflorum × Asiatic (LA) and Oriental × Asiatic (OA), were used. Mostly the BC progenies of LA hybrids consisted of both triploid (2n = 3x = 36) and diploid (2n = 2x = 24) with some aneuploid genotypes and those of OA hybrids consisted of triploid (2n = 3x = 36) and some aneuploid genotypes. In all cases, it was possible to identify the homoeologous recombinant chromosomes as well as accurately count the number of crossover points, which are called “recombination sites”. Recombination sites were estimated in the BC progeny of 71 LA and 41 OA genotypes. In the case of BC progenies of LA hybrids, 248 recombination sites were cytologically localized on 12 different chromosomes of each genome (i.e., L and A). Similarly, 116 recombinant sites were localized on the 12 chromosomes each from the BC progenies of OA hybrids (O and A genomes). Cytological maps were constructed on the basis of the percentages of distances (micrometres) of the recombination sites from the centromeres. Since an Asiatic parent was involved in both hybrids, viz. LA and OA, two maps were constructed for the A genome that were indicated as Asiatic (L) and Asiatic (O). The other two maps were Longiflorum (A) and Oriental (A). Remarkably, the recombination sites were highly unevenly distributed among the different chromosomes of all four maps. Because the recombination sites can be unequivocally identified through GISH, they serve as reliable landmarks and pave the way for assigning molecular markers or desirable genes to chromosomes of Lilium and also monitor introgression of alien segments. Des cartes de recombinaison chromosomique ont été produites pour les trois génomes du lys (Lilium) au moyen d&x2019;analyses GISH. Pour y arriver, les progénitures rétrocroisées (BC) de deux hybrides interspécifiques du lys (2n = 2x = 24), i.e. Longiflorum × Asiatic (LA) et Oriental × Asiatic (OA) ont été employées. Pour la plupart les descendants BC des hybrides LA étaient triploïdes (2n = 3x = 36) ou diploïdes (2n = 2x = 24) en plus des quelques génotypes aneuploïdes alors que ceux des hybrides OA étaient triploïdes (2n = 3x = 36) avec quelques génotypes aneuploïdes. Dans tous les cas, il a été possible d&x2019;identifier les chromosomes homéologues recombinants et de compter précisément le nombre d&x2019;enjambements, lesquels sont appelés des sites de recombinaison. Le nombre de sites de recombinaison a été estimé chez les progénitures BC des 71 génotypes LA et des 41 génotypes OA. En ce qui a trait aux progénitures BC des hybrides LA, 248 sites de recombinaison ont été localisés par examen cytologique sur les 12 chromosomes de chacun des génomes (L et A). De manière semblable, 116 sites de recombinaison ont été situés sur les 12 chromosomes de chaque génome (O et A) au sein des progénitures BC des hybrides OA. Des cartes cytologiques ont été produites sur la base du pourcentage des distances (micromètres) séparant les sites de recombinaison et les centromères. Puisqu&x2019;un parent Asiatic était impliqué dans les deux hybrides, LA et OA, deux cartes ont été construites pour le génome A et celles-ci ont été nommées Asiatic (L) et Asiatic (O). Les deux autres cartes ont été nommées Longiflorum (A) et Oriental (A). Remarquablement, les sites de recombinaison étaient répartis très inégalement sur les différents chromosomes sur les quatre cartes. Comme les sites de recombinaison sont identifiables sans équivoque par analyse GISH, ils peuvent servir de repères et ouvrent la voie à l&x2019;assignation de marqueurs moléculaires ou de gènes à des chromosomes chez le genre Lilium ainsi qu&x2019;au suivi de l&x2019;introgression de segments étrangers. [ABSTRACT FROM AUTHOR]

A set of trisomics of Chinese cabbage was used for determining the n+1 gamete transmission rate and locating the gene controlling 2n gamete formation on the corresponding chromosome. The results showed that the transmission rates of extra chromosomes in different trisomics varied from 0% to 15.38% by male gametes and from 0% to 17.39% by female gametes. Of the nine F2 populations derived from the hybridizations between each trisomic and Bp058 (2n gamete material), only Tri-4×Bp058 showed that the segregation ratio of plants without 2n gamete formation to plants with 2n gamete formation was 10.38:1, which fitted the expected segregation ratio of the trisomics (AAa) based on the 7.37% of n+1 gamete transmission through female and 5.88% through male. In other populations the segregation ratios varied from 2.48:1 to 3.72:1, which fitted the expected 3:1 segregation ratio of the bisomics (Aa). These results suggested that the gene controlling 2n gamete formation in Chinese cabbage Bp058 was located on chromosome 4. Further trisomic analysis based on the chromosome segregation and the incomplete stochastic chromatid segregation indicated that the gene locus was tightly linked to the centromere. [ABSTRACT FROM AUTHOR]

The quantity and quality of pollen produced by a genotype are important attributes to be considered in the selection of male parents for breeding. The objective of this research was to determine the quantity and quality of pollen in 13 selected East African Highland bananas (EAHB) in relation to six diploids commonly used as male parents. Pollen quantity was scored on a scale of 0–6 while the variation of pollen stainability along the rachis was determined using acetocarmine glycerol jelly. Actual male fertility was determined by using pollen from the EAHB varieties on M. acuminata spp. burmannicoides, ‘Calcutta 4’, as the female. The diameter of 200 viable pollen grains was measured under a microscope with the aid of a graduated eyepiece. Significant differences were obtained for mean pollen stainability and pollen diameter. The pollen stainability for diploids was higher than that for the EAHB. Node numbers contributed significantly to variation of pollen stainability in EAHB ( P ≤ 0.01) and ‘Pisang lilin’ ( P ≤ 0.001). ‘Pisang lilin’ and the EAHB varieties had about 100 nodes as opposed to about 200 in other diploids. The EAHB varieties produced less pollen than most of the diploids. The actual male fertility of EAHB varieties was low (1 seed/bunch), compared to that of ‘Calcutta 4’ (223.3 seeds/bunch) and ‘Pisang lilin’ (13.7 seeds/bunch). Although the production of 2 n pollen in EAHB varieties was low (0–7%), the potential exists for using them in new breeding approaches. [ABSTRACT FROM AUTHOR]

The article highlights a study which details meiotic and postmeiotic abnormalities related to cytokinesis in microsporogenesis in Brachiaria (B.) humidicola. An analysis of 25 accessions of B. humidicola from the African savannas was made cytologically. It says that the cytological method revealed one accession presenting several meiotic abnormalities.

With the aim of utilizing allotriploid (2 n = 3 x = 36) lily hybrids ( Lilium) in introgression breeding, different types of crosses were made. First, using diploid Asiatic lilies (2 n = 2 x = 24), reciprocal crosses (3 x − 2 x and 2 x − 3 x) were made with allotriploid hybrids (AOA) obtained by backcrosses of F1 Oriental × Asiatic hybrids (OA) to Asiatic cultivars (A). Secondly, the AOA allotriploids were crossed with allotetraploid (OAOA, 2 n = 4 x = 48), in 3 x − 4 x combination. Finally, the AOA allotriploids where crossed to 2 n gamete producer F1 OA hybrids (3 x − 2 x (2 n)). Two types of triploids were used as parents in the different types of crosses, derived from: (a) mitotic polyploidization and (b) sexual polyploidization. Ploidy level of the progeny was determined by estimating the DNA values through flowcytometry as well as chromosome counting. The aneuploid progeny plants from 3 x − 2 x and reciprocal crosses had approximate diploid levels and in 3 x − 4 x crosses and 3 x − 2 x (2 n) the progeny had approximate tetraploid levels. Balanced euploid gametes ( x, 2 x and 3 x) were formed in the AOA genotypes. Recombinant chromosomes were found in the progenies of all crosses, except in the case of 2 x − 3 x crosses through genomic in situ hybridization (GISH) analyses. Recombinant chromosomes occurred in the F1 OA hybrid when the triploid AOA hybrid was derived through sexual polyploidization, but not through mitotic polyploidization with two exceptions. Those recombinant chromosomes were transmitted to the progenies in variable frequencies. [ABSTRACT FROM AUTHOR]

Based on the size differences found between haploid and diploid pollen produced by diploid and tetraploid rose cultivars, respectively, 2 n pollen producers were identified in a population of 53 diploid hybrids from a cross between a dihaploid rose, derived from the haploidization of a tetraploid modern cultivar and the diploid species R. wichuraiana. Frequency of 2 n pollen producers was estimated in 2002, 2003 and 2004. Highly variable frequencies were found i) within population; ii) during years of observation (between years and between different months in the same year). The variation of 2 n pollen production could be related to environmental fluctuations. A cytological analysis of male meiosis was carried out in 10 hybrids randomly chosen. Among meiotic abnormalities leading to 2 n pollen formation, triads (containing a 2 n microspore at one pole and two n microspores at the other) resulting from abnormal spindle geometry were frequently observed. The mode of 2 n pollen formation is genetically equivalent to a First Division Restitution (FDR) mechanism. FDR 2 n pollen transmits a high percentage of the heterozygosity from the diploid parent – 2 n pollen producer-to the tetraploid offspring. [ABSTRACT FROM AUTHOR]

There is no better use of sexual reproduction in regard to breeding and genetic research than the ploidy level manipulations possible in the potato and its relatives. Unique reproductive characteristics of tuber-bearing Solanum species make possible: the production of gametes with unreduced chromosome number; the presence of an endosperm dosage system that regulates success of interploidy/interspecific crosses; the possibility to easily extract maternal haploids following crosses with S. phureja. This paper reviews results obtained in scaling genomic multiples up and down in potato, and relates these manipulations to breeding strategies for the genetic improvement of the cultivated potato. Several ploidy series have been developed, ranging from the monoploid to the hexaploid level. Cultivated tetraploids were scaled down to the diploid and monoploid level by haploidy. Scaling upward was achieved by sexual polyploidisation via 2n gametes that resulted in triploid, tetraploid, pentaploid, and hexaploid genotypes with a broad genetic base. Altogether, the success of ploidy level manipulations constitutes further proof that sexual polyploidisation played an important role in the polyploid evolution of Solanum species, and supports the idea that gene flow can be relatively easily accomplished through interploid and bridge crosses. [ABSTRACT FROM AUTHOR]

Many diploid rose species and cultivars possess valuable traits that can be introgressed into modern tetraploid cultivars. Interspecific, interploidy crosses are possible, but triploid hybrids typically have limited fertility, hindering further breeding and selection. Tetraploidizing diploids before mating with tetraploids can alleviate fertility barriers. The efficiency of trifluralin was investigated for polyploidization ofRosa chinensis minima(2n= 2x= 14) seedlings. Treatments were trifluralin at 0.086% and 0.0086%, colchicine (0.5%), and distilled water and contained 2% dimethyl sulfoxide and a surfactant. Approximately 5 µl of the treatment solution was applied to the apical meristem of seedlings (N= 337, 82-85 per treatment) in the process of cotyledon expansion. Guard cell length, pollen diameter, and root tip squashes of rooted cuttings were used to detect polyploidy in meristematic layer (L)I, LII, and LIII, respectively. Trifluralin (0.086%) was the most effective treatment for polyploidization (LI 20.2%, LII 12.9%, LIII 12.9%), followed by trifluralin (0.0086%) (LI 10.6%, LII 7.1%, LIII 4.7%) and colchicine (LI 2.4%, LII 0%, LIII 0%). Polyploidization consistently occurred from LI inward. Polyploids as a group had reduced pollen stainability and a lower leaflet length to width ratio than diploids. In addition, two diploid seedlings were identified which produce 2npollen. Considerations in selecting germplasm and generating somatically-induced polyploids from seedlings versus clones for use in breeding are discussed. [ABSTRACT FROM AUTHOR]

Meiosis is a fascinating and complex phenomenon with intriguing practical potential. Some deviations in meiotic reduction are crucial for plant evolution and extremely important for plant breeding. In particular, the production of gametes with unreduced chromosome number and the diplosporic pathway of apomixis hold great promise for the genetic improvement of cultivated plants. The use of meiotic mutations is hampered by the fact that they do not occur widely in crop plants, and traditional breeding approaches to transfer these characters are difficult or impossible. For their exploitation, genetic engineering has been suggested as a promising and more direct way. Since molecular advances for isolating meiotic genes in flowering plants have been pursued mostly in Arabidopsis thaliana, mutants of this plant with alterations in meiotic reduction or meiotic nuclear restitution are the main focus of this review. Emphasis has been given to the cytological description of mutated phenotypes, their effect on male/female fertility, and to gene function. Perspectives for using meiotic genes of Arabidopsis to manipulate whole genomes through 2n gametes and for the exploitation of apomixis are also discussed. [ABSTRACT FROM AUTHOR]

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The widespread occurrence of 2n gametes (i.e. gametes with the somatic chromosome number) in the Medicago sativa-coerulea-falcata complex supports the concept that gene flow from diploid to tetraploid species occurs continuously in nature and plays a key role in alfalfa evolution. Breeders realized early that gene transfer between ploidy levels via 2n pollen and 2n eggs would have had potential use in cultivated alfalfa improvement. Cytological investigations provided insights into the types of meiotic abnormalities responsible for the production of 2n gametes. Alterations were defined as genetically equivalent to first (FDR) or second division restitution (SDR) mechanisms. For breeding purposes, data have proven that 2n gametes of the FDR type are more advantageous than those obtained by SDR for transferring parental heterozygosity and retaining epistatic interactions. The use of diploid meiotic mutants that produce 2n gametes is now recognized as one of the most effective methods available for exploiting heterosis and introgressing wild germplasm traits into cultivated tetraploid alfalfa via unilateral (USP) and bilateral sexual polyploidization (BSP) schemes. Both 2n egg and 2n pollen producers could be used for direct gene transfer from wild diploid relatives into cultivated alfalfa by means of 2x-4x and 4x-2x crosses. Although data have shown that forage yield improvement can be achieved when plants are sexually tetraploidized, problems related to reduced plant fertility and seed production remain largely unexplained. Apomixis has the potential of cloning plants through seed and thus provides a unique opportunity for developing superior tetraploid cultivars with permanently fixed heterosis and epistatic effects. A main goal in alfalfa breeding could be the introduction of functional apomixis (i.e. apomeiosis and parthenogenesis) in cultivated alfalfa stocks. In the future, the efficiency of alfalfa breeding programs based on the use of reproductive mutants could be improved by direct selection at the genotype level using RFLPs and PCR-based markers. Suitable DNA markers and detailed linkage maps of alfalfa mutants should help to discover apomictic mutants and address basic genetic issues such as the extent of genomic recombination in polyploid hybrids and the effect of sexual polyploidization on heterosis. Molecular markers have recently been used in alfalfa for studying the inheritance of 2n gamete formation and identifying polymorphisms associated to genes involved in meiotic abnormalities. Molecular tagging of 2n egg and 2n pollen formation not only should explain the genetic control and regulation of these traits, but may also be an essential step towards marker-assisted selection of 2n gamete producers and implementation of USP and BSP breeding schemes. Future perspectives include strategies for the map-based cloning of genomic DNA markers, and screening of EST mini-libraries related to flowers at different developmental stages from meiotic mutants and wild-types can lead to the identification of mRNAs and thus of candidate genes that control 2n gamete formation in alfalfa. [ABSTRACT FROM AUTHOR]

An analysis of microsporogenesis was carried out in four populations of Pfaffia tuberosa (2n=4x=68) and in ten populations of P. glomerata (2n=2x=34). Monads, dyads and triads were reported at high frequency in all populations of P. tuberosa. In P. glomerata, on the other hand, only four populations presented monads, and at low frequency. Dyads and triads were observed in both species, albeit at a higher frequency in P. tuberosa populations. Certain abnormalities of spindles in the second division, such as sequential and tripolar spindles, led to triad formation by the rejoining of two chromosome sets. The precise causes of monad and dyad formation have not been found during meiosis, although evidence exists that dyads originated by omission of second meiosis and monads by omission of both meiotic divisions. [ABSTRACT FROM AUTHOR]

Genus Vaccinium, consisting of blueberries, cranberries, lingonberries and many related wild species, includes diploid, tetraploid, and hexaploid species. Most evidence indicates that the tetraploid species are autotetraploids, with non-preferential bivalent chromosome pairing. Although homoploid interspecific crosses usually produce numerous fertile hybrids if the parents are from the same section of the genus, intersectional crosses at the diploid level normally produce no seedlings, weak seedlings, or seedlings that are very low in fertility. There is a strong but not complete triploid block within Vaccinium. Even within sections, tetraploid × diploid (and the reciprocal) crosses normally give only a few tetraploid and a few triploid hybrids. Hexaploid × diploid crosses within sections are very hard to make, and the few hybrids that have been obtained are pentaploid. The frequency of 2n gametes varies, both among genotypes within species and among species. Vaccinium pollen is normally shed in tetrads, and the frequency of large pollen grains shed in dyads can be used to estimate 2n gamete frequency. Cultivated blueberries occur at both the tetraploid and the hexaploid levels, and there are important genetic resources in the diploids. Unreduced gamete production has permitted transfer of genetic material from the diploid to the tetraploid level and from the diploids and tetraploids to the hexaploid level via triploid hybrids. Intersectional crosses can occasionally produce tetraploid Vaccinium hybrids that appear to behave as amphidiploids and have medium to high fertility. Commercial Vaccinium cultivars are normally propagated by cuttings. Intersectional hybridization, chromosome doubling, and asexual propagation could permit the production of novel hybrid combinations with value as ornamentals or in fruit production. [ABSTRACT FROM AUTHOR]

Colchicine induced polyploids have not directly contributed for crop improvement in the past. On the other hand, the so-called natural polyploids, derived from the functioning of numerically unreduced (2n) gametes have been shown to be more relevant for crop improvement in many cases. Different types of cytological abnormalities during meiosis can give rise to 2n gametes and the genetic composition of these gametes is variable. Depending on the type meiotic abnormalities, various types of 2n gametes, such as first division restitution (FDR), second division restitution (SDR), indeterminate meiotic restitution (IMR) and post meiotic restitution (PMR) gametes, among others, have been described in recent years. For the improvement of autopolyploids such as potato, alfalfa, Vaccinium spp., and some of the fodder grasses, FDR gametes have been proved to be highly useful. However, the use of 2n gametes for the improvement of allopolyploid crops has received much less attention so far. Some of the investigations on allopolyploids, derived from Festuca-Lolium, Alstroemeria and Lilium species hybrids, have revealed that 2n gametes can be most useful for the introgression of alien genes and chromosomes into cultivars. An important feature of using sexual polyploidization in the case of allopolyploids is that introgression can be achieved through recombination due to genetic crossing-over between alien chromosomes as well as addition of alien chromosomes, which is extremely difficult or impossible to achieve in the case of colchicine induced allopolyploids. Because of the recent developments in the field of plant molecular biology, methods have become available for the analysis of 2n gametes and sexual polyploid progenies more accurately and to develop systematic breeding approaches. The methods include DNA in situ hybridization (GISH and FISH) and molecular mapping (AFLP, RFLP, RAPDs). In addition to providing basic information on the genetic and genome composition of the polyploid progenies, these methods can be potentially useful for a more efficient creation of desirable breeding material and cultivars. [ABSTRACT FROM AUTHOR]

Abstract The study examined the effect of ploidy elevation through unreduced gametes on transgene expression in potato. Tetraploid transgenic progenies were obtained from one tetraploid potato cultivar crossed with 2n pollen producing diploid clones harbouring an exogenous transgene (cry3Aa ). Both single- and multiple-insert diploid transgenic lines that were regenerated by Agrobacterium tumefaciens leaf disc inoculation were used in crosses. A DAS–ELISA system and no-choice feeding bioassay enabled characterization of the parental lines as either ‘high’ or ‘low’ expressers of the Cry3Aa protein. High Cry3Aa expression was observed for both single-insert transgenic diploids and their 4x –2x progeny. On the contrary, 68% of 4x –2x progeny derived from a multiple-insert, diploid transgenic had significantly reduced Cry3Aa expression compared with the parent, with 32% demonstrating nearly complete silencing of the transgene. Multiple copies of a transgene, like homologous native genes, may be susceptible to transgene silencing following polyploidization. Therefore, incorporation of exogenous transgenes into a true potato seed (TPS) production system is feasible if a single-insert diploid parent is used. Gene-centromere mapping of the cry3Aa transgene demonstrated that a non-transgenic refuge might be naturally created in a TPS hybrid system through genetic recombination. [ABSTRACT FROM AUTHOR]

Abstract Chromosome number, microsporogenesis and mode of reproduction are described for an accession of Brachiaria brizantha , a grass of African origin. Cytological analysis revealed that the accession BRA005886 is pentaploid (2n = 5x = 45), with a base number of x = 9. Multivalent chromosome associations, from tri- to pentavalents, were recorded in diakinesis, and the further meiotic behaviour was highly irregular as well. Most abnormalities were related to irregular chromosome segregation commonly found in polyploids. Micronuclei were observed following telophases I and II. Some micronuclei near the cell wall were released as microcytes, whereas others remained in the tetrad. Other meiotic abnormalities, such as cell fusion and the absence of cytokinesis causing the formation of dyads and triads were also recorded. Binucleate microspores and 2n microspores resulting from nucleus restitution were observed among the normal ones. Limitations of this accession for use in hybridization programmes are discussed. [ABSTRACT FROM AUTHOR]

Cytology and breeding behavior of Solanum commersonii – S. tuberosum hybrids derived from 3x × 4x crosses was examined. The chromosome number of hybrids ranged from hypo-pentaploid (2n=5x – 8=52), to hyper-pentaploid (2n=5x + 7=67), with the euploid pentaploid 2n=5x=60 class predominant. The high variability in chromosome number of the 3x × 4x hybrids was attributed to the fact that meiotic restitution during megasporogenesis of the 3x female may have involved poles with various chromosome numbers, resulting in 2n eggs with 24–48 chromosomes. Microsporogenesis analyses provided evidence that chromosome pairing between S. commersonii and S. tuberosum genomes occurred. In addition, chromosome distribution at anaphase I and anaphase II revealed an average chromosome number of 29.5 and 29.1 per pole, respectively. To further study the extent of transmission of extra genome chromosomes from pentaploids, 5x × 4x and 4x × 5x crosses were performed, and the chromosome number of resulting progeny was determined. Ploidy ranged from 2n=4x=48 to 2n=5x=60 following 5x × 4x crosses, and from 2n=4x + 1=49 to 2n=5x=60 following 4x × 5x crosses. These results provided indirect evidence that the pentaploid hybrids produced viable aneuploid gametes with a chromosome number ranging from 24 to 36. They also demonstrated that gametes with large numbers of extra chromosomes can be functional, resulting in sporophytes between the 4x and 5x ploidy level. Fertility parameters of crosses involving various (aneuploid) pentaploid genotypes were not influenced by chromosome number, suggesting a buffering effect of polyploidy on aneuploidy. The possibility of successfully using (aneuploid) pentaploid genotypes for further breeding efforts is discussed. [ABSTRACT FROM AUTHOR]

Cold-chipping cultivars could reduce microbial spoilage and chemical use due to cold storage of chipping potatoes. Sexual polyploidization breeding schemes that introgress cold chipping from diploid potato species may develop improved cultivars at an accelerated rate. The research objectives were (1) to determine the breeding behavior of cold chipping introgressed from 2× 2 Endosperm Balance Number (EBN) potato species into 4×(4EBN) progeny using sexual polyploidization, and (2) to determine if differences exist between 2n gametes and n tetrasomic gametes for transmission of cold chipping. Experimental families of 4×(4EBN) progeny were synthesized using sexual polyploidization (2× × 4× and 4× × 2×) and 4× × 4× matings using cold-chipping S. phureja and cultivated potato -wild species (C -W) hybrid parents. Control families from 4× × 4× matings using as parents current industry leading germplasm were also made. Progeny were field grown and evaluated for chip color (1 light-10 dark, ≤4.0 is industry acceptable) after 3 and 6 months storage at 4 C. A larger percentage of progeny from experimental families had acceptable chip color compared to control families, likely due to introgression of cold-chipping alleles from diploid potato species. Out of experimental families, the best chip color means, highest phenotypic variance, and greatest percentage of acceptable chipping progeny resulted in 2× × 4× and 4× × 2× matings. The ability of 2n gametes to transmit dominant alleles to high frequencies of 4× progeny may contribute to the superiority of 4× -2× crosses. Breeding schemes that use sexual polyploidization in conjunction with early generation selection should rapidly develop 4× cold-chipping germplasm. [ABSTRACT FROM AUTHOR]