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1.
The aim of this work was to obtain a series of genetically related lines of Eragrostis curvula with different ploidy levels and reproductive modes, which can be used for the discovery of genes associated to diplospory. E. curvula is a widely cultivated forage grass native to Southern Africa that reproduces naturally by obligate diplosporous apomixis (asexual reproduction by seeds) of the Antennaria type. In vitro culture of immature inflorescences of the apomictic cultivar Tanganyika led to the regeneration of a diploid plant with a particular morphology (plant UNST1122). Embryo sac analysis and progeny tests determined that plant UNST1122 reproduces by sexuality. UNST1122 was cloned by dividing its tillers and a R 1 generation was obtained from seeds after open pollination among the diploid clones. A set of 500 seeds from a diploid R 1 plant was treated with colchicine and two plants showing a duplicated chromosome number (2n = 4x = 40) were obtained (plants UNST1112 and UNST1131). Progeny tests using RAPDs indicated that these plants reproduce also by sexuality. The availability of sexual tetraploid genotypes of E. curvula will allow the production of hybrids with new interesting combinations of agronomic traits and the developing of mapping populations segregating for diplospory. Besides, these genetically related plants with different reproduction modes constitutes an excellent model for the identification of gen(es) involved in diplosporous apomixis by mRNA profiling as well as to study the genomic rearrangements and gene expression alterations associated to changes at ploidy levels.  相似文献   

2.
St. John's wort (Hypericum perforatumL.) is a medicinal crop plant that reproduces by apomixis. To study the reproductive diversity within the initial breeding material, 656 plants from 92 accessions of the species were analysed by flow cytometric seed screening (FCSS) and compared to 66 plants of cv. ‘Topaz’ as a control. Among plants from the 92 accessions, 16 were obligate sexuals, nine were obligate apomicts and all remaining ones were facultative apomicts. Among controls, there were six obligate and 60 facultative apomicts. Tests of reproductive pathways indicated that, in the investigated collection, all apomictic plants were tetraploid and all sexual plants were diploid. A strategy for a cross breeding program in St. John's wort is illustrated by crossing one diploid obligately sexual mother plant with six tetraploid facultative apomicts. All 91 F1 progeny obtained were triploid with 58% being obligate sexuals and 42% facultative apomicts. To quantify the different routes of seed formation within facultatively apomictic individuals, the reproductive pathways were reconstructed from about 30 single seeds from each of five tetraploid and two triploid plants using FCSS. The frequency of seed formed by apomixis ranged from 54% to 67% among four tetraploid genotypes. One triploid and two tetraploids formed 23% to 73% of the so-called BIII hybrids (fertilization of unreduced eggs) and one triploid was obligately sexual. The results show that while the mode of reproduction in H. perforatum is highly variable, tetraploid obligate apomicts as well as diploid and triploid obligate sexuals can be selected as starting material for breeding purposes. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

3.
New efforts to overcome apomixis in Poa pratensis L.   总被引：1，自引：0，他引：1  
F. Matzk 《Euphytica》1991,55(1):65-72
Summary By means of a new method, plants of Poa pratensis can be classified rapidly and reliably as to whether they are capable or incapable of parthenogenesis. Parthenogenesis was found to be under strong genetic control, dominant over obligatory fertilization. The selected sexual plants lack all genes/alleles responsible for parthenogenesis, while the polyploid apomictic varieties investigated were heterozygous with one or more dominant alleles. Also dosage effects and/or modifying genes are probably involved. Crosses of sexual individuals with various apomictic varieties resulted in sexual as well as highly apomictic F1 hyrids. A scheme of recurrent hybridization for breeding of Kentucky bluegrass is proposed.Two other experimental ways to overcome apomixis in Poa pratensis were studied in addition. By application of growth regulators temporary sexuality could not be induced. Attempts of in vitro regeneration of plants from endosperm resulted only in callus and root formation.  相似文献   

4.
Apomixis involves the parthenogenetic development of apomeiotic eggs. It has the potential of cloning plants through seed, and thus furnishes a unique opportunity in breeding of allogamous sexual species, such as alfalfa, for developing superior cultivars with permanently fixed heterosis. Apomixis as a whole has not been detected in the genus Medicago, but components of apomixis have been reported. The formation of unreduced eggs through diplosporic meiosis was documented in a diploid mutant of M. saliva ssp. falcata (L.) Arcang., named PG-F9. Since in facultative apomictic species non-reductional meiosis and parthenogenesis could be tightly associated processes, a progeny test based on morphological trait and molecular marker evaluation was carried out to verify the occurrence of parthenogenesis in PG-F9. Morphological traits such as leaf shape, stipule form, stem pigmentation and flower colour were shown to be effective in the preliminary screening of progenies and most of the plants were classified as non-maternal (i.e. from sexual reproduction). Molecular investigations by means of random amplified polymorphic DNA (RAPD) fingerprint and heterozygous restriction fragment length polymorphism (RFLP) loci detection conducted on the progenies classified morphologically as maternal allowed two plants, molecularly similar but not identical to PG-F9, to be discovered. Owing to the high number of molecular markers conserved as in the mother plant, and because of the great discriminating efficiency of the primers and probes used, these progeny plants could most likely be generated through parthenogenesis of diplosporic eggs. In fact, the extraordinary preservation of maternal morphological traits and genomic loci over one generation may be explained only if apomictic reproductive events rarely took place in PG-F9.  相似文献   

5.
Camilo L. Quarin 《Euphytica》1986,35(2):515-522
Summary Changes in incidence of apomixis were determined at different intervals of the flowering period in a highly sexual diploid cytotype of Paspalum cromyorrhizon Trin., a natural tetraploid cytotype of the same species, and in the triploid and tetraploid intraspecific hybrids that were produced by pollinating the 2x cytotype with pollen of the tetraploid. Reproductive behaviour was determined from observations of embryo sacs in mature ovules. Gametophytic apomixis in this species in characterized by aposporous embryo sacs which differ from normal sacs by their number, orientation inside the ovule, their dimensions and shape, and the absence of antipodal cells.The potential for apomictic reproduction increased in relation to the ploidy level, suggesting a gene dosage effect in the incidence of apomixis. In the three ploidy levels, the highest incidence of apomixis was observed when the plants reached the maximum number of flowering heads. These findings suggest that the same environmental conditions that favour flowering should also be responsible for increasing the incidence of apomixis. An additional experiment under controlled conditions indicated that the light regime should be one of the factors that govern the amount of apomictic reproduction. Thus, polyploidy and apomixis should be of special significance in the dispersion and evolution of this grass species. The 4x facultative apomictic cytotype is far more frequent in nature than the highly sexual 2x. Moreover, most of the seeds produced in a flowering season should arise asexually. So, apomixis rapidly increases the number of plants bearing the successful maternal genotype, and sexual reproduction becomes important in adverse environmental conditions.  相似文献   

6.
Intergeneric hybridization was performed between Moricandia arvensis and four inbred lines of Brassica rapa following embryo rescue. Three F1 hybrid plants were developed from three cross combinations of M. arvensis × B. rapa, and amphidiploids were synthesized by colchicine treatment. Six BC1 plants were generated from a single cross combination of amphidipolid × B. rapa ‘Ko1-303’ through embryo rescue. One BC2 and three BC3 plants were obtained from successive backcrossing with B. rapa ‘Ko1-303’ employing embryo rescue. Alloplasmic and monosomic addition lines of B. rapa (Allo-MALs, 2n = 21) were obtained from backcrossed progeny of three BC3 plants (2n = 21, 22 and 23) without embryo rescue. An alloplasmic line of B. rapa (2n = 20) degenerated before floliation on 1/2 MS medium due to severe chlorosis. Allo-MALs of B. rapa (2n = 21) showed stable male sterility without any abnormal traits in vegetative growth and female fertility. Molecular analyses revealed that the same chromosome and cytoplasm of M. arvensis had been added to each Allo-MAL of B. rapa. This Allo-MAL of B. rapa may be useful material for producing cytoplasmic male sterile lines of B. rapa.  相似文献   

7.
The objectives of this study were to evaluate the tolerance to low temperatures and tuber soft rot in hybrids between Solanum commersonii and Solanum tuberosum. The experimental materials consisted of F1 triploid, BC1 pentaploid‐near pentaploid and BC2 tetraploid–near tetraploid hybrids. The F1 triploids had a freezing tolerance and acclimatization capacity closest to S. commersonii. This indicated that the endosperm barriers which prevent the introgression of 1EBN S. commersonii into 4EBN S. tuberosum had been overcome. Indeed, the triploids produced 2n eggs, thus giving a compatible maternal to paternal EBN ratio in the hybrid endosperm generated by the 3x(2EBN) × 4x(3EBN) crosses. The tolerance to low temperatures of BC1 and BC2 hybrids was lower than that of the F1. However, a number of genotypes were identified which were able to withstand temperatures down to ‐5°C. Some BC2 hybrids were also tested for their tolerance to tuber soft rot, and some resistant hybrids were detected. A number of them combined the capacity for cold acclimatization with tolerance to tuber soft rot. These hybrids have an EBN of 4; they are fertile and have been used in backcrosses with 4EBN S. tuberosum.  相似文献   

8.
B. S. Ahloowalia 《Euphytica》1982,31(1):103-111
Summary Aneuploid plants of perennial ryegrass (Lolium perenne L.) with 2n=15 to 30 chromosomes were obtained by crossing a near-triploid (2n=3x+1=22) with a diploid or on open-pollination with diploids and tetraploids. Aneuploids occurred with a frequency of 83% in near triploid × diploid progeny and 92% on open-pollination with diploid and tetraploid plants. Aneuploid plants with 15 to 18 chromosomes resembled diploids in morphology and those with 19 to 30 chromosomes were akin to tetraploids. Meiotic studies suggested that most aneuploid plants resulted from transmission of aneuploid egg cells (n=8 to 23). Aneuploid plants with 2n=27 to 30 chromosomes in the progeny of 22×14 cross originated from unreduced egg cells. Plants with 19 to 21 chromosomes were recovered only by immature seed culture. Aneuploid plants with 26 to 30 chromosomes and triploids (2n=21) had higher pollen fertility and bigger seeds than plants with 15 to 22 chromosomes.  相似文献   

9.
Rice tungro disease (RTD) is one of the destructive and prevalent diseases in the tropical region. RTD is caused by Rice tungro spherical virus (RTSV) and Rice tungro bacilliform virus. Cultivation of japonica rice (Oryza sativa L. ssp japonica) in tropical Asia has often been restricted because most japonica cultivars are sensitive to short photoperiod, which is characteristic of tropical conditions. Japonica1, a rice variety bred for tropical conditions, is photoperiod-insensitive, has a high yield potential, but is susceptible to RTD and has poor grain quality. To transfer RTD resistance into Japonica1, we made two backcrosses (BC) and 8 three-way crosses (3-WC) among Japonica1 and RTSV-resistant cultivars. Among 8,876 BC1F2 and 3-WCF2 plants, 342 were selected for photoperiod-insensitivity and good grain quality. Photoperiod-insensitive progenies were evaluated for RTSV resistance by a bioassay and marker-assisted selection (MAS), and 22 BC1F7 and 3-WCF7 lines were selected based on the results of an observational yield trial. The results demonstrated that conventional selection for photoperiod-insensitivity and MAS for RTSV resistance can greatly facilitate the development of japonica rice that is suitable for cultivation in tropical Asia.  相似文献   

10.
Hybrid sterility hinders the transfer of useful traits between Oryza sativa and O. glaberrima. In order to further understand the nature of interspecific hybrid sterility between these two species, a strategy of multi-donors was used to elucidate the range of interspecific hybrid sterility in this study. Fifty-nine accessions of O. glaberrima were used as female parents for hybridization with japonica cultivar Dianjingyou 1, after several backcrossings using Dianjingyou 1 as the recurrent parent and 135 BC6F1 sterile plants were selected for genotyping and deducing hybrid sterility QTLs. BC6F1 plants containing heterozygous target markers were selected and used to raise BC7F1 mapping populations for QTL confirmation and as a result, one locus for gamete elimination on chromosome 1 and two loci for pollen sterility on chromosome 4 and 12, which were distinguished from previous reports, were confirmed and designated as S37(t), S38(t) and S39(t), respectively. These results will be valuable for understanding the range of interspecific hybrid sterility, cloning these genes and improving rice breeding through gene introgression.  相似文献   

11.
Given that feral transgenic canola (Brassica napus) from spilled seeds has been found outside of farmer’s fields and that B. juncea is distributed worldwide, it is possible that introgression to B. juncea from B. napus has occurred. To investigate such introgression, we characterized the persistence of B. napus C genome chromosome (C-chromosome) regions in backcross progenies by B. napus C-chromosome specific simple sequence repeat (SSR) markers. We produced backcross progenies from B. juncea and F1 hybrid of B. juncea × B. napus to evaluate persistence of C-chromosome region, and screened 83 markers from a set of reported C-chromosome specific SSR markers. Eighty-five percent of the SSR markers were deleted in the BC1 obtained from B. juncea × F1 hybrid, and this BC1 exhibited a plant type like that of B. juncea. Most markers were deleted in BC2 and BC3 plants, with only two markers persisting in the BC3. These results indicate a small possibility of persistence of C-chromosome regions in our backcross progenies. Knowledge about the persistence of B. napus C-chromosome regions in backcross progenies may contribute to shed light on gene introgression.  相似文献   

12.
In crossing diploid male-sterile beets (18 chromosomes) with a tetraploid pollinator (36 chromosomes) it was established that of 532 individuals from this cross 8.4% were diploid, 83.9% triploid and 7.7% tetraploid.The most reasonable explanation was that the diploid male-sterile plants had given a number of unreduced egg cells. This could be put to a test by crossing diploid male-sterile plants with normal diploids. The average number of triploids found by chromosome counts was 2.4%; in a normal diploid no triploids were found.The type of cytoplasm associated with the male-sterility may lead to abnormal egg cells.Trirave (Triplex) with 84% of triploids, represents an enormous advance over normal polyploid types, which very commonly have no more than 40 per cent triploids and very rarely have more than 50 per cent.Bush Johnsons Limited and D.J. van der Have n.v.Paper read on the XXIInd Winter Meeting of the Institut International de Recherches Betteravières on February 24th, 1959.  相似文献   

13.
Summary Atrazine resistant Brassica napus × B. oleracea F1 hybrids were backcrossed to both parental species. The backcrosses to B. napus produced seeds in both directions but results were much better when the F1 hybrid was the pollen parent. Backcrosses to B. oleracea failed completely but BC1s were rescued by embryo culture both from a tetraploid hybrid (2n = 4x = 37; A1C1CC) and sesquidiploid hybrids (2n = 3x = 8; A1C1C). Progeny of crosses between the tetraploid hybrid and B. oleracea had between 25 and 28 chromosomes. That of crosses between the sesquidiploid hybrid and B. oleracea had between 21 and 27. A few plants that had chromosome counts outside the expected range may have originated from either diploid parthenogenesis, unreduced gametes or spontaneous chromosome doubling during in vitro culture. Pollen stainability of the BC1s ranged from 0% to 91.5%. All the BC1s to B. oleracea were resistant to atrazine.  相似文献   

14.
B. J. Kim    Y. C. Kwon    Y. H. Kwack    M. S. Lim  E. H. Park 《Plant Breeding》1999,118(5):439-442
Fourteen interspecific hybrids in sexual diploid Allium senescens var. minor× apomictic tetraploid Allium nutans L. crosses, and eight interspecific hybrids in sexual diploid A. senescens var. minor× apomictic hexaploid A. senescens L. crosses were produced. The number of chromosomes was 2n= 24 in interspecific hybrids of diploid × tetraploid, and 2n= 32 in diploid × hexaploid crosses. Triploid and tetraploid interspecific hybrids showed intermediate parental morphological characteristics. Tetraploid interspecific hybrids of A. senescens var. minor×A. senescens crosses formed two groups based on leaf colour and leaf width. Seeds were formed in 11 out of 14 triploid interspecific hybrids under natural conditions. In cytological observations of parthenogenesis, three out of 12 triploid interspecific hybrids and five out of eight interspecific tetraploid hybrids were observed. Parthenogenesis ranged from 26.0% to 86.0% in five tetraploid interspecific hybrids. Non-parthenogenesis to parthenogenesis segregated in a 3:5 ratio in A. senescens var. minor×A. senescens crosses.  相似文献   

15.
Summary Cajanus platycarpus, an incompatible wild species from the tertiary gene pool of pigeonpea (C. cajan (L.) Millspaugh), has many desirable characteristics for the improvement of cultivated varieties. To necessitate such transfers, embryo rescue techniques were used to obtain F1 hybrids. The F1 hybrids were treated with colchicine to obtain tetraploid hybrids, that were selfed to obtain F2, F3 and F4 progenies. All of the hybrids and subsequent progenies had an intermediate morphology between the two parents. Backcrossing of the tetraploid hybrids with cultivated pigeonpea was not possible given embryo abortion, with smaller aborted embryos than those obtained in the F0 parental cross.As a route of introgression, diploid F1 hybrids were backcrossed with cultivated pigeonpea and BC1 progeny obtained by in vitro culture of aborting embryos. BC2 plants were obtained by normal, mature seed germination. Although embryo rescue techniques had to be used to obtain F1 and BC1 plants, it was possible to produce BC2 and subsequent generations through direct mature seed. Every backcross to cultivated pigeonpea increased pollen fertility and the formation of mature seeds.Special project assistant till December, 2003.  相似文献   

16.
Somatic hybrids between Sinapis alba (2n= 24) and Brassica oleracea (2n= 18) have been backcrossed with the B. oleracea parent. Whereas backcrosses with the diploid B. oleracea parent were unsuccessful, 344 BC1 seeds could be obtained from inter-valence crosses with tetraploid B. oleracea (2n= 4x= 36). The investigated 96 BC1 plants segregated for morphological traits and for fertility. They were backcrossed with diploid B. oleracea or self-pollinated, depending on their male fertility. The BC1F2 and BC2 progenies segregated well for the morphological traits. Disturbances were observed especially in the generative phase (flower development and pollen fertility). Both male fertile and male sterile BC1F2 and BC2 plants were obtained and backcrossed or self-pollinated with the B. oleracea parent. The presence of either one of the parental or the cybrid organelle genomes was detected. In the progenies, a stable maternal inheritance of the organelle genome patterns was observed. Isozyme analyses revealed polymorphism for the leucine aminopeptidase (LAP) which was used for the identification of S. alba genes in the progenies. Cytological investigations showed a clear differentiation between the BC1F2 and BC2 plants. Whereas the BC1F2 plants possess large numbers of chromosomes ranging from 34 to 40, the BC2 material was strongly reduced to chromosome numbers ranging from 20 to 22. Preliminary investigation of the meiosis suggests the possibility of introgressions of S. alba-DNA into the B. oleracea genome.  相似文献   

17.
Summary By crossing amphimictic P. longifolia and apomictic P. pratensis fertile hybrids were obtained. In F2 populations a vast range of types was observed. New combinations were found, which is shown by data on plant length and hairiness of the lemma. Crossing F1 hybrids with P. pratensis gave more P. pratensis-like plants. Data on seed yield, uniformity and turf performance in later generations are given. The implications for breeding are discussed and it is concluded that interspecific crosses can be used for introducing a sexual phase in P. pratensis breeding. Non-hairiness of the lemma can be incorporated.  相似文献   

18.
Marker assisted backcrossing has been used effectively to transfer the submergence tolerance gene SUB1 into popular rice varieties, but the approach can be costly. The selection strategy comprising foreground marker and phenotypic selection was investigated as an alternative. The non-significant correlation coefficients between ranking of phenotypic selection and ranking of background marker selection in BC2F1, BC3F1 and BC3F2 generations indicated inefficiency of phenotypic selection compared to marker-assisted background selection with respect to recovery of the recipient genome. In addition, the introgression size of the chromosome fragment containing SUB1 was approximately 17 Mb, showing the effects of linkage drag. The significant correlation coefficient between rankings of phenotypic selection with the percentage of recipient alleles in the BC1F1 generation suggested that background selection could be avoided in this generation to minimize the genotyping cost. The phenotypically selected best plant of the BC3F1 generation was selfed and backcross recombinant lines were selected in the resulting BC3F4 generation. The selection strategy could be appropriate for the introgression of SUB1 QTL in countries that lack access to high-throughput genotyping facilities.  相似文献   

19.
Summary InDactylis glomerata L. subsp.lusitanica, triploid and tetraploid plants were obtained by bilateral sexual polyploidization in crosses between diploid parents known to produce 2n gametes. The polyploid and diploid progeny were compared for allozyme diversity (allele number and heterozygosity), phenological (pollen fertility, inflorescence emergence date), cellular (stomatic cell size) and morphological characters (vegetative biomass, seed weight, total seed number per plant, panicle number and seed number per panicle length) in four contrasting growing conditions. Stomatal cell size and the total number of alleles were significantly lower in diploids than in polyploids which sometimes recovered more than two distinct alleles at a locus via 2n gametes possessing heterozygous loci. Pollen fertility was similar in diploids and tetraploids, but significantly lower in the triploids. Seed weight was significantly higher in polyploids, although the average number of seeds per panicle length and the total number of seeds was higher in the diploid sibs. No phenological differences occurred among ploidy levels whereas such differences were observed inDactylis in all the natural areas of sympatry between diploids and their related polyploids. Our results provide evidence for an instantaneous effect of polyploidization on certain traits and suggest that natural selection would act subsequently on several other traits to allow the establishment of new polyploids.  相似文献   

20.
Fingerprinting of alfalfa meiotic mutants using RAPD markers   总被引：5，自引：0，他引：5  
Summary A calendar of female sporogenesis and gametogenesis was made for both apomictic tetraploid (2n=4x=36) Brachiaria brizantha and Brachiaria decumbens and their apomictic F1 hybrids with sexual tetraploid (2n=4x=36) Brachiaria ruziziensis. Microgametogenesis was used as a reference. Apospory was facultative in both species and hybrids. Environmental conditions had variable effects on the level of apomixis according to each genotype. Ratios of segregation into sexuals and apomicts in the interspecific hybrids suggest an oligogenic determinism with dominant apomixis in the genus Brachiaria. Highly apomictic and partially male fertile hybrids were identified and will be used in an improvement program to transfer genes for apomixis into the sexual species B. ruziziensis.  相似文献   

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