Search

ABSTRACTApomixis is a mode of asexual reproduction through seed. Apomixis can be classified into two types – gametophytic and sporophytic apomixis. The phenomenon of apomixis in higher plants is limited; however, it seems to play a critical role in the genetic diversity of Garcinia species. Many species in Garcinia undergo apomixis and this review highlights reproductive pathways of various Garcinia species documented over the years. Most of the Garcinia species are endemic. Garcinia species are known for their edible fruits. For the conservation of species and maintenance of genetic diversity, it is necessary to understand the processes by which Garcinia species reproduce.

Genus Garcinia shows high diversity of sexual systems; most of them are dioecious in nature. The other reported sexual systems of Garcinia include gynodioecious, androdioecious, monoecious, and andromonoecious. Garcinia indica (Thouars) Choisy was reported as facultative apomictic polygamodioecious species. There is a large diversity in floral types. Hence, a detailed study of various floral types found on different types of plants of G. indica and to correlate its functionality with sexual reproduction was undertaken. The study at Kokum Plot, BSSKVV, Dapoli, revealed that the male plants could be categorized into four types – androecious, functional males, andromonoecious, and hermaphrodites. The female plants displayed large variation in number and viability of stamens/staminodes. Each category showed significant difference in phenology, floral morphology and pollen types. In December, the percentage of staminate flowers (79.13 ± 2.93%) in androecious trees was significantly higher than functional males (58.61 ± 8.60%) or andromonoecious trees (56.36 ± 2.77%) (p ≤ .01). As female plants started flowering, all male morphotypes bore significantly higher numbers of staminate flowers and carpellate flowers were significantly reduced. Pollen viability was highest in androecious flowers at 90.11 ± 1.10% and lowest at 64.70 ± 2.09% in hermaphrodite trees. Earlier studies reported female flowers bore well-developed female gametophyte, but the embryo development was not observed. Thus, the fruit formation might be apomictic, but in present embryological investigation; more than 60% of female and andromonoecious flowers, a well-developed embryo was formed between 8 and 24 h after anthesis. Thus, the embryo formation might be sexual or apomictic. Floral types favoring sexual reproduction are essential for conservation of highly endemic species.

Apomixis is a mode of asexual reproduction through seed. Apomixis can be classified into two types – gametophytic and sporophytic apomixis. The phenomenon of apomixis in higher plants is limited; however, it seems to play a critical role in the genetic diversity of Garcinia species. Many species in Garcinia undergo apomixis and this review highlights reproductive pathways of various Garcinia species documented over the years. Most of the Garcinia species are endemic. Garcinia species are known for their edible fruits. For the conservation of species and maintenance of genetic diversity, it is necessary to understand the processes by which Garcinia species reproduce. [ABSTRACT FROM AUTHOR]

Most apomictic plants are facultative, maintaining the ability to reproduce sexually at different frequencies depending on the taxa, ploidy, and reproductive stage. In this context, Paspalum species are good model systems for studies evaluating the varying levels of apomixis expression. We aimed to identify, in apomictic tetraploid Paspalum species, the degree of apomixis and residual sexuality in three stages of reproductive development, and if their expression varies along them in order to predict their realized impact on the genetic diversity of future generations. Three main stages in the reproductive development (i.e., ovule, seed, and progeny) were studied in tetraploids from populations of P. cromyorhizon and P. maculosum. Mature ovules were studied using cytoembryological analysis, seeds by flow cytometry, and progeny tests with molecular markers. The expression of sexuality and apomixis was compared in each stage. We observed a decline in expression of sexual reproduction through the consecutive stages, jointly with an increase of apomixis expression. Both species showed at least one tetraploid plant capable of producing progeny by sexual means. These small rates of sexually originated progeny prove the ability of apomictic plants to produce low levels of genetic variation through rare events of sexuality. This study also demonstrates the importance of analyzing different reproductive stages in order to get a whole picture of the reproductive outcomes in plant evolution. [ABSTRACT FROM AUTHOR]

Genus Garcinia shows high diversity of sexual systems; most of them are dioecious in nature. The other reported sexual systems of Garcinia include gynodioecious, androdioecious, monoecious, and andromonoecious. Garcinia indica (Thouars) Choisy was reported as facultative apomictic polygamodioecious species. There is a large diversity in floral types. Hence, a detailed study of various floral types found on different types of plants of G. indica and to correlate its functionality with sexual reproduction was undertaken. The study at Kokum Plot, BSSKVV, Dapoli, revealed that the male plants could be categorized into four types – androecious, functional males, andromonoecious, and hermaphrodites. The female plants displayed large variation in number and viability of stamens/staminodes. Each category showed significant difference in phenology, floral morphology and pollen types. In December, the percentage of staminate flowers (79.13 ± 2.93%) in androecious trees was significantly higher than functional males (58.61 ± 8.60%) or andromonoecious trees (56.36 ± 2.77%) (p ≤.01). As female plants started flowering, all male morphotypes bore significantly higher numbers of staminate flowers and carpellate flowers were significantly reduced. Pollen viability was highest in androecious flowers at 90.11 ± 1.10% and lowest at 64.70 ± 2.09% in hermaphrodite trees. Earlier studies reported female flowers bore well-developed female gametophyte, but the embryo development was not observed. Thus, the fruit formation might be apomictic, but in present embryological investigation; more than 60% of female and andromonoecious flowers, a well-developed embryo was formed between 8 and 24 h after anthesis. Thus, the embryo formation might be sexual or apomictic. Floral types favoring sexual reproduction are essential for conservation of highly endemic species. [ABSTRACT FROM AUTHOR]

Introduction and objectives: The genus Pilosella is native to Europe and Asia, but its species are successful invaders on most continents. These species form an agamic complex with common apomixis. Apomictic species hybridize and have different degree of residual sexuality. Main aim of this paper was to determine if interspecific hybridization already occurred in Patagonia. M&M: We analysed seed progeny collected at thirteen populations of Pilosella in southern Argentina and Chile. The taxonomic identity of plants, DNA ploidy level (using flow cytometry), chromosome number, reproduction, formation of parthenogenetic seeds and clonal identity (using isozyme phenotypes) were examined. Results: No mixed-species population was recorded. Two apomictic clones of P. officinarum (one pentaploid and the other hexaploid) were found in populations: eight were hexaploid and one was mixed in cytotype composition. A new species for Patagonia, the apomictic pentaploid P. caespitosa, was represented by plants from two Argentinean populations. Some of the progeny plants, cultivated from seeds sampled at three localities, represented seed-fertile aneuploids the morphology of which suggest a hybrid origin with P. officinarum as one of the parental species. Conclusions: The presence of seed-fertile, aneuploid and parthenogenetic hybrids among the cultivated plants signifies an increased risk of the formation of new hybridogeneous genotypes of Pilosella in southern Patagonia. [ABSTRACT FROM AUTHOR]

Introduction and objectives: The members of the genus Pilosella are native in Europe and Asia, but they are successful invasive species on most continents. These species form an agamic complex with common apomixis. Apomictic species hybridize, they have different degree of residual sexuality. Main aim of this paper was to determine if the interspecific hybridization already occurred in Patagonia. M&M: This study is based on analysis of seed progeny collected at thirteen populations of Pilosella in southern Argentina and Chile. The plants were examined for their taxonomic identity, DNA ploidy level (using flow cytometry), chromosome number, reproduction, formation of parthenogenetic seeds and clonal identity (using isozyme phenotypes). Results: No mixed-species population was recorded. Two apomictic clones of P. officinarum (one pentaploid and the other hexaploid) were found in populations: eight were hexaploid and one was mixed in cytotype composition. A new species for Patagonia, the apomictic pentaploid P. caespitosa, was represented by plants from two populations in Argentina. Some of the progeny plants cultivated from seeds sampled at three localities represented seed-fertile aneuploids the morphology of which implied a hybrid origin and indicated P. officinarum as one of the parents. Conclusions: The presence of seed-fertile, aneuploid and parthenogenetic hybrids among the cultivated plants signifies an increased risk of the formation of new hybridogeneous genotypes of Pilosella in southern Patagonia.

Most apomictic plants are facultative, maintaining the ability to reproduce sexually at different frequencies depending on the taxa, ploidy, and reproductive stage. In this context, Paspalum species are good model systems for studies evaluating the varying levels of apomixis expression. We aimed to identify, in apomictic tetraploid Paspalum species, the degree of apomixis and residual sexuality in three stages of reproductive development, and if their expression varies along them in order to predict their realized impact on the genetic diversity of future generations. Three main stages in the reproductive development (i.e., ovule, seed, and progeny) were studied in tetraploids from populations of P. cromyorhizon and P. maculosum. Mature ovules were studied using cytoembryological analysis, seeds by flow cytometry, and progeny tests with molecular markers. The expression of sexuality and apomixis was compared in each stage. We observed a decline in expression of sexual reproduction through the consecutive stages, jointly with an increase of apomixis expression. Both species showed at least one tetraploid plant capable of producing progeny by sexual means. These small rates of sexually originated progeny prove the ability of apomictic plants to produce low levels of genetic variation through rare events of sexuality. This study also demonstrates the importance of analyzing different reproductive stages in order to get a whole picture of the reproductive outcomes in plant evolution.

Kokum (Garcinia indica) tree is endemic to Western Ghats region of India. Commercially, Kokum fruits are well-known for anti-obesity factor hydroxy citric acid as well as for their UV protecting activity. Locally, it is also used for culinary purposes and preparing healthy beverages. Still, due to endemicity and unreliable fruit production, this plant is largely underutilized. In the current study, a controlled pollination experiment was performed on three sets of female flowers to determine the need of pollination for fruit set. The set of flowers bagged without pollination did not show any fruit set, suggesting the need of pollen stimulus for the fruit setting. In artificially and naturally pollinated flowers, a well-developed female gametophyte was seen after 12 days from anthesis, but zygotic embryo or endosperm was not detected suggesting apomictic fruit set. The possibility of apomixis was also studied at the molecular level for a known male and two female plants and their F1 progenies with the help of ISSR markers. The majority of F1 progenies showed a banding pattern identical to the female parent indicating apomixis, while a few progenies showed different banding patterns, suggesting sexual reproduction. Therefore, it appears that the G. indica reproduces via facultative apomixis. [ABSTRACT FROM AUTHOR]

Some citrus varieties express a form of apomixis termed nucellar embryony in which the adventive embryos develop from nucellus tissue surrounding the embryo sac. This trait results in many seeds containing multiple embryos (polyembryony). Inheritance of the frequency of polyembryony was studied in 88 progeny from a cross of Citrus maxima (monoembryonic) × Poncirus trifoliata (polyembryonic). The frequency of polyembryonic seed produced by each progeny was determined by scoring 100–500 seeds for the number of seedlings to emerge from each seed. Two groups of eight individuals from each extreme of the population were chosen for bulked segregant analysis with amplified fragment length polymorphism markers amplified with 256 primer combinations. Candidate markers identified in the bulks as linked to the trait were tested on the 32 individuals used to create the bulks and then on the remaining plants in the population. Five candidate markers tightly linked to polyembryony in P. trifoliata were identified. Specific marker alleles were present in nearly all progeny that produced polyembryonic seed, and alternate alleles were present in nearly all progeny that produced only monoembryonic seed. The region defined by these markers very likely contains a gene that is essential for the production of polyembryonic seeds by apomixis, but also shows segregation distortion. The proportion of polyembryonic seeds varied widely among the hybrid progeny, probably due to other genes. Scoring 119 progeny of a P. trifoliata selfed population for the closely linked markers and the proportion of polyembryonic seeds confirmed close linkage between these markers and polyembryony.

The species-mixed Pilosella populations comprising diploid sexual and polyploid facultatively apomictic biotypes were studied in Bulgaria. Parentage of co-occurring recent hybrids was inferred from a combination of morphology and ploidy level that corresponded to simple/multiple crosses of basic species via either reduced or unreduced gametes. The flow cytometric seed screening illustrated the capacity for heteroploid hybridization both in open-pollinated plants in the mixed-ploidy populations and in crossing experiments. The diploid sexual species in Bulgaria have a limited impact on interspecific hybridization, and simple inter-cytotype hybrids are only sporadically formed. The origin of the most common hybrids in Bulgaria that are apomictic and retain the pentaploid/hexaploid ploidy level of a co-occurring putative apomictic parent remains unclear. The absence of stabilized hybridogeneous species and scarcity of commonly hybridizing polyploid sexual biotypes are crucial attributes that distinguish the Pilosella populations in Bulgaria from those in the Czech Republic and Germany. No recent high-polyploid hybrids of 2n + n origin that would potentially become drivers of ongoing hybridization in the mixed sexual-apomictic Pilosella populations similar to those in Central Europe have been recorded in Bulgaria. The pattern of co-occurring cytotypes in Bulgaria likely limits interspecific hybridization due to stronger ploidy barriers. Citation: Krahulcová A., Krahulec F. & Vladimirov V. 2018: Impact of interspecific hybridization within a polyploid agamic complex of Pilosella (Asteraceae, Cichorieae) in Bulgaria compared with Central Europe. – Willdenowia 48: 345–362. doi: https://doi.org/10.3372/wi.48.48302 Version of record first published online on 8 October 2018 ahead of inclusion in December 2018 issue. [ABSTRACT FROM AUTHOR]

Plant development by the apomixis process has a significant impact on agriculture and food production. Analysis of the amphimictic and apomictic modes of reproduction is important for breeding new varieties and control of high-quality seeds and fruits. Fragaria x ananassa is one of the most often cultivated plants characterized by a wide assortment of commercially available cultivars. The aim of this study was to describe all phases of female gametophyte development in F. x ananassa cv. ‘Mount Everest’ and ‘Senga Sengana’. In this paper, we report both typical stages of the sexual pathway of development and events indicating the possibility of the apomictic mode in the examined strawberry ovules. The beginning of the F. x ananassa reproduction process is distinguished by the presence of a multicellular archespore. With the progress in the development, the particular features of the ovule show a tendency towards simultaneous formation of multiple megasporocytes and embryo sacs in the same nucellus. Our results may be taken as evidence of the occurrence of facultative apomixis in both examined cultivars of F. x ananassa. [ABSTRACT FROM AUTHOR]

Background and aims Arabinogalactan proteins are present in the extracellular matrix and their occurrence is developmentally regulated. The studies were carried out to localise arabinogalactan proteins in ovary cells of Fragaria x ananassa Duchesne (strawberry) during megasporogenesis, megagametogenesis, and formation of the embryo. Methods The research included studies of ovary histochemistry and immunofluorescence labelling of AGP epitopes was performed with antibodies JIM13, JIM15 and MAC207. The use of the immunogold labelling method allowed specific detection of AGP epitopes at the subcellular level. Key results The localization of AGPs was studied in the cells of the ovary wall and elements building the developing ovule i.e. the integument, nucellus, archespore, megaspores, embryo sac, and embryo of a facultative apomict Fragaria x ananassa cv. 'Mount Everest'. For the first time the presence of AGP epitopes at the stage of a multicellular archespore was described. The occurrence of AGPs in the functional megaspore walls is related to selection of a megaspore continuing development; during later stages of development, AGPs are also evident markers of the female gametophyte. The intense fluorescence indicates the presence of AGPs in the embryo sac wall as well as in the cytoplasm compartment of the egg apparatus and around the secondary nucleus of the central cell. The localization of AGPs in the ovule of F . x ananassa resembles the distribution of these proteins in amphimictic plants. Conclusions Arabinogalactan proteins occur in similar parts of the ovule of amphimictic and apomictic plants. The results confirm the participation of AGPs in reproductive structures as a useful marker during development of female gametophyte. [ABSTRACT FROM AUTHOR]

Traditionally, tetraploid Paspalum notatum was considered an obligate or a facultative apomict according to cytoembryological analyses. The degree of facultativeness was usually determined by the relative amount of mature ovules bearing aposporous or meiotic (sexual) embryo sacs, or both together. We established, through progeny tests conducted with the aid of AFLP markers, the degree of residual sexuality expressed in four selected biotypes. The results showed it to be substantially and significantly lower than predicted by previous embryological analyses for the same biotypes. Moreover, the lowest expression of residual sexuality was coincident with maximum flowering period. Seed development in facultative apomictic P. notatum shows a definite bias against meiotic embryo sacs.

We studied the significance of sexual reproduction as a source of ploidy level variation in a model system consisting of hexaploid, facultatively apomictic Pilosella bauhini and tetraploid, sexual P. officinarum. As the maternal parent, apomictic P. bauhini generated higher ploidy level variation than sexual P. officinarum. Ploidy levels of its progeny ranged from triploid to octoploid under experimental conditions and even to decaploid in the field. This progeny diversity resulted from the breeding system in P. bauhini, which included haploid parthenogenesis and sexual reproduction through both reduced and unreduced gametes besides prevailing apomixis; these particular reproductive pathways have been quantified. Sexual P. officinarum, on the other hand, reproduced exclusively through fusion of reduced gametes and produced only pentaploid hybrids or tetraploid progeny from autogamy, allogamy or both. Surprisingly, sexual P. officinarum was also the species showing stronger reproductive isolation, especially under the field conditions where intra-specific fertilization was highly favoured, most probably through competition between conspecific and heterospecific pollen. Apomictic P. bauhini thus appeared to be a significant source of ploidy level variation in the model population even though most of its progeny was formed clonally through apomixis. Only part of this variation was manifested in the field. [ABSTRACT FROM AUTHOR]

The effect of maternal, facultatively apomictic plants on population diversity was evaluated in seven hybridizing polyploid Pilosella populations, where apomictic ( P. bauhini or P. aurantiaca) and sexual ( P. officinarum) biotypes coexist. The ploidy level, reproductive system, morphology, clonal structure and chloroplast DNA haplotypes were used to characterize these plants and their hybrids. The reproductive origins of the progeny were assessed through either a flow cytometric seed screen and/or a comparison between the ploidy level of progeny embryos/seedlings and the maternal ploidy level. The cultivated progeny derived from residual sexuality in maternal apomicts were also identified based on their morphology and reproductive behaviour. The progeny different from their maternal parents (0.6−92.3 % of progeny embryos and 0−100 % of progeny seedlings) originated either sexually or via haploid parthenogenesis. Comparing the facultatively apomictic and sexual mothers, the progeny arrays generated in the field showed that apomictic mothers produce progeny that is more variable in ploidy level. This effect was demonstrated at both the embryonic and seedling stages of progeny development. Residual sexuality in apomicts was also effective in experimental crosses, generating progeny similar to spontaneous hybrids in the field. The 2 n + n hybrids produced from an apomictic and a sexual parent displayed similar reproductive behaviour, producing polyhaploid, sexual and apomictic progeny in variable ratios. Repeated hybridizations between parental species and/or multi-step crosses can result in hybrid swarms rich in cytotypes and morphotypes. The variation recorded in these populations suggests prevailing introgressive hybridization towards the sexual species P. officinarum. [ABSTRACT FROM AUTHOR]

The article discusses the findings of a study to understand the role of hybridization in the evolution of the section Niveae for the Potentilla family of flowering plants. It notes that researchers tested two hybridization hypotheses that included a proposed a potential hybrid for Potentilla nivea and Potentilla arenosa, and between Potentilla arenosa and Potentilla vahliana sensu lato. The study infers the efficacy of morphometric studies in confirming the taxonomic potential of the hybrids.

The inheritance of glyphosate resistance in two Amaranthus palmeri populations (R1 and R2) was examined in reciprocal crosses (RC) and second reciprocal crosses (2RC) between glyphosate-resistant (R) and -susceptible (S) parents of this dioecious species. R populations and Female-R × Male-S crosses contain higher 5-enolpyruvylshikimate-3-phosphate synthase ( EPSPS) gene copy numbers than the S population. EPSPS expression, EPSPS enzyme activity, EPSPS protein quantity, and level of resistance to glyphosate correlated positively with genomic EPSPS relative copy number. Transfer of resistance was more influenced by the female than the male parent in spite of the fact that the multiple copies of EPSPS are amplified in the nuclear genome. This led us to hypothesize that this perplexing pattern of inheritance may result from apomictic seed production in A. palmeri. We confirmed that reproductively isolated R and S female plants produced seeds, indicating that A. palmeri can produce seeds both sexually and apomictically (facultative apomixis). This apomictic trait accounts for the low copy number inheritance in the Female-S × Male-R offsprings. Apomixis may also enhance the stability of the glyphosate resistance trait in the R populations in the absence of reproductive partners. [ABSTRACT FROM AUTHOR]

Abstract: Buffel grass (Cenchrus ciliaris L. syn. Pennisetum ciliare (L.) Link) is a species that is highly tolerant to drought and is used primarily as forage in drier regions throughout the subtropics and tropics. It reproduces mainly by apomixis and the acquisition of obligate sexual genotypes or facultative apomicts with high levels of sexuality is required for performing crosses and plant improvement. The aim of this study was to obtain sexual genotypes from controlled crosses using obligate apomictic cultivars and a sexual line. Twelve putative hybrid F1 plants were selected morphologically and two of them were identified as sexual genotypes by PCR using specific primers for reproductive mechanism. Cytoembryological analysis showed 65.5 and 71.3% meiotic embryo sacs in these plants and their hybrid nature was corroborated by AFLP. Both highly sexual genotypes could be used as female parents in crosses for obtaining improved cultivars of buffel grass. [Copyright &y& Elsevier]

Traditionally, tetraploid Paspalum notatum was considered an obligate or a facultative apomict according to cytoembryological analyses. The degree of facultativeness was usually determined by the relative amount of mature ovules bearing aposporous or meiotic (sexual) embryo sacs, or both together. We established, through progeny tests conducted with the aid of AFLP markers, the degree of residual sexuality expressed in four selected biotypes. The results showed it to be substantially and significantly lower than predicted by previous embryological analyses for the same biotypes. Moreover, the lowest expression of residual sexuality was coincident with maximum flowering period. Seed development in facultative apomictic P. notatum shows a definite bias against meiotic embryo sacs. [ABSTRACT FROM AUTHOR]

Reproductive variation was studied in the tetraploid Pilosella aurantiaca, hexaploid P. rubra (both species with facultative autonomous apospory) and in their 2 n + n hybrids, which were obtained by crossing with a sexual pollen parent (tetraploid P. officinarum). The different DNA content in P. aurantiaca and P. officinarum demonstrated the actual 2 n + n origin, both spontaneous from the field and through experimental crosses, of their hexaploid hybrids. The octoploid 2 n + n progeny were recovered from an experimental cross of P. rubra and P. officinarum. The reproductive pathways operating in two maternal facultatively apomictic species and in the hybrids were quantified using a flow cytometric analysis of seeds obtained from either open-pollinated or emasculated plants. Whereas both maternal species displayed a high penetrance of apomixis, the level of apomixis among the majority of 2 n + n hybrids was much lower and variable. Some of the hexaploid hybrids had a reduced seed set. Compared to the respective maternal parents, the decrease in apomixis due to haploid parthenogenesis and/or n + n mating was evident in almost all unreduced hybrids, irrespective of their field/experimental origin and ploidy. Hence, the reproductive behaviour in the apomictic maternal parent was profoundly different from that of the 2 n + n hybrids with a sexual parent in spite of the preservation of the complete maternal genome in the hybrids. The regulatory interactions in hybrid genomes, such as effects of modifiers, heterochrony, and epigenetic control, may be consistent with the different expressivity of apomixis observed under different genetic backgrounds. [ABSTRACT FROM AUTHOR]

Various aspects of the reproductive success of Garcinia atroviridis Griff. were studied. Controlled pollination experiments were carried out in an orchard located in Songkhla province, southern Thailand, from February to July 2003. Floral longevity, stigma receptivity, and pollen viability were examined before carrying out the experiments. Three pollination treatments were compared: open pollination, manual pollination with bags, and bags without pollination (apogamy). Although there was no significant difference in the initial fruit set, bagged and manual pollination produced a significantly greater fruit drop rate than apogamy or natural pollination at one week after the flowers had been pollinated. On the other hand, the apogamy treatment had a greater fruit drop rate than natural and manual pollination treatments before fruit maturation. In addition, unpollinated bagged flowers bore fewer and smaller fruit than naturally and manually cross-pollinated flowers. Although the fruits from unpollinated flowers were capable of asexual seed formation, they produced fewer seeds and had poorer seed quality (defined as average fresh weight and germination rate) than those from the other treatments. The occurrence of asexual and sexual reproduction was also studied using Random Amplification of Polymorphic DNA (RAPD) analysis and by comparing the patterns of bands produced from DNA extracted from the offspring of the naturally cross-pollinated fruits. On average, 58% of the offspring had a genetic constitution identical to that of the maternal parent (ranging from 36% to 87%), indicating that some offspring were produced without prior fertilisation. However, the remainder showed polymorphism, demonstrating the occurrence of sexual reproduction. These findings indicate that facultative apomixis occurred in the study population. However, a residual sexuality was important for fruit production, fruit size, normal seed set and seed quality. [ABSTRACT FROM AUTHOR]

The capacity to generate variation in ploidy and reproductive mode was compared in facultatively apomictic versus sexual maternal plants that coexist in two model populations. The population structure was studied in polyploid hybrid swarms comprised of Hieracium pilosella (usually sexual, less commonly apomictic), H. bauhini (apomictic), and their hybrids (sexual, apomictic, or sterile). Relationships among established biotypes were proposed on the basis of their DNA ploidy level/chromosome number, reproductive mode and morphology. Isozyme phenotypes and chloroplast DNA haplotypes were assayed in the population that was richer in hybrids. The reproductive origin of seed progeny was identified in both sexual and apomictic mothers, using alternative methods: the karyological, morphological and reproductive characters of the cultivated progeny were compared with those of respective mothers, or flow cytometric seed screening was used. In both populations, the progeny of sexual mothers mainly retained a rather narrow range of ploidy level/chromosome number, while the progeny of facultatively apomictic mothers was more variable. The high-polyploid hybrids, which had arisen from the fertilization of unreduced egg cells of apomicts, mainly produced aberrant non-maternal progeny (either sexually and/or via haploid parthenogenesis). Apparently, such versatile reproduction resulted in genomic instability of the recently formed high-polyploid hybrids. While the progeny produced by both true apomictic and sexual mothers mostly maintained the maternal reproductive mode, the progeny of those ‘versatile’ mothers was mainly sexual. Herein, we argue that polyploid facultative apomicts can considerably increase population diversity. [ABSTRACT FROM AUTHOR]

Selection within progeny of a facultative apomict, Hieracium rubrum, was studied using flow cytometry of embryos in seeds (a modified method of Flow Cytometric Seed Screen) and seedlings. Flow cytometric screening of particular progeny classes was based on distinct ploidy categories, reflecting the way of their origin. The results of both estimations of progeny composition significantly differed, which makes direct comparison of proportions detected in seeds or seedling stage impossible. The results suggest that progeny originating from reduced egg cells have higher mortality during germination and the early establishment phase than that from unreduced egg cells. Within the progeny of emasculated plants, the proportion of polyhaploid progeny decreased in favor of apomictically derived plants. Within the progeny of plants pollinated by H. pilosella, the proportion of polyhaploid progeny decreased significantly in favor of apomictically derived plants and 2n + n hybrids. It is argued that at least a proportion of the sexually derived progeny of this facultatively apomictic maternal parent has a lower survival rate than apomictically derived progeny. [ABSTRACT FROM AUTHOR]

Reproductive behaviour and the pathways of gene flow among ploidy levels were studied experimentally in Taraxacum sect. Ruderalia. Diploid, triploid and tetraploid individuals were sampled from mixed diploid -- polyploid natural populations. 136 experimental hybridizations between the plants of different ploidy levels were performed. Seeds resulting from these crosses, those obtained from isolated anthodia as well as from open pollinated anthodia (both from cultivated and wild plants) were subjected to the flow-cytometric seed screening (FCSS) to determine ploidy levels in the progeny and to infer breeding behaviour of maternal plants. Three possible pathways of the gene flow were studied: (A) fertilization of sexuals by pollen of apomicts, (B) BIII hybrid formation, (C) facultative apomixis. Diploid maternal plants when experimentally crossed with triploid pollen donors produced diploids and polyploid progeny, while when pollinated with a mixture of the pollen of diploids and triploids or insect pollinated, no polyploids were discovered. It seems that in the mixture with the pollen of diploids, the pollen of triploids is ineffective. Tetraploids produce hybrids much easier with diploid mothers and their role in wild populations requires further study. Triploid mothers, even those with subregular pollen did not show traces of facultative apomixis. BIII hybrids were present in the progeny of both triploids and tetraploids, in tetraploids in quite high percentages (up to 50% of the progeny in some crosses). [ABSTRACT FROM AUTHOR]

The genetic base of guayule ( Parthenium argentatum Gray) germ plasm that is available is narrow; yet, significant variability has been described within this germ plasm. This variability is surprising because guayule reproduces by facultative apomixis (asexual reproduction by seed), but evidence suggests that progress through selection is feasible. It has been hypothesized that this variation has arisen through periodic sexual reproduction; however, this has not been quantified. This study was designed to describe and compare eight components of yield and the expression of two isozyme systems in twenty parent plants and half-sib, open-pollinated families from each parent. Extensive variation for all characters was found among both the parents and the progeny, with fresh and dry weights being highly correlated to rubber yield. Parent-offspring regressions were not significantly different from zero. This implies low heritabilities for the major components of yield in guayule, and we believe that family selection, rather than single-plant selection, may generate higher-yielding and more genetically uniform lines at an escalated rate than single-plant selection. Periodic sexuality resulting in genetic variation was estimated by differences in isozyme expression within the half-sib families. Fifteen of the twenty progeny families were polymorphic for either esterase or peroxidase or both isozymes. This amount of sexuality is significant, and guayule must be considered an open-pollinated crop. We conclude from this study that we should rethink our breeding procedures to include controlled pollination and family selection. [ABSTRACT FROM AUTHOR]