Monohaploids (n=x=12) from autotetraploid Solanum tuberosum (2n=4x=48) through two successive cycles of female parthenogenesis

Summary Viable monohaploids with 12 chromosomes in their somatic cells were obtained from an autotetraploid cultivar of Solanum tuberosum (2n=4x=48) by inducing female parthenogenesis successively in the tetraploid cultivar and in dihaploids from that cultivar. Both dihaploids and monohaploids were induced using the diploid S. phureja clones IvP 35 and IvP 48 as pollinators. The average frequencies of dihaploids and monohaploids in 1973 were 2.0 and 0.14 per berry respectively.Non-homologous chromosome associations (bivalents, trivalents and even quadrivalents) were observed at metaphase I of meiosis in pollen mother cells of the two monohaploids studied.The occurrence of non-homologous associations of chromosomes during meiosis is discussed. In addition the potential significance of monohaploids for basic research andfor breeding of potatoes is considered.     

Discovery of 2n gametes in tetraploid oat Avena vaviloviana

Summary Sexual polyploidization via the action of 2n gametes (gametes with the sporophytic chromosome number) has been identified as the most important evolutionary mode of polyploidization among plant genera. This study was conducted to determine whether 2n gametes are present in the tetraploid level of the genus Avena (2n=4×=28) Twenty tetraploid Avena lines, representing four species and one interspecific hybrid, were screened for pollen grain size in order to differentiate between n and 2n pollen. Avena vaviloviana (Malz.) Mordv. line PI 412767 was observed to contain large pollen grains at a 1.0% frequency. Cytogenetic analyses of pollen mother cells of PI 412767 revealed cells with double the normal chromosome number (i.e., 56 chromosomes at metaphase I and anaphase I). The mode of chromosome doubling was found to be failure of cell wall formation during the last mitotic division that preceded meiosis. The resulting binucleate cells underwent normal meiotic divisions and formed pollen grains with 28 chromosomes. Based on the formation and function of 2n gametes, three models involving diploid and tetraploid oat lines are proposed to describe possible evolutionary pathways for hexaploid oats. If stable synthetic hexaploid oat lines could be developed by utilizing 2n gametes from diploid and tetraploid oat species through bilateral sexual polyploidization, the resulting hexaploids could be used in breeding programs for transferring genes from diploids and tetraploids to cultivated hexaploids.     

Cytology and reproductive behavior of diploid, tetraploid and hexaploid germplasm accessions of a wild forage grass: Paspalum compressifolium

Summary Fourteen germplasm accessions of Paspalum compressifolium native from southern Brazil were cytologically and embryologically analysed. The study revealed that one accession was diploid (2n=20), twelve were tetraploid (2n=40) and one was hexaploid (2n=60). This is the first report of diploid and hexaploid cytotypes for this species. Studies on microsporogenesis, megasporogenesis, and embryo sac development indicated that the diploid cytotype had regular meiotic behavior and reproduces sexually. Tetraploid cytotype usually had an important proportion of chromosomes that associated as quadrivalents during meiosis and reproduced by mean of aposporous apomixis. The hexaploid cytotype showed irregular meiotic behavior with about one third of the chromosomes associated as multivalents and reproduced by aposporous apomixis. Thus, P. compressifolium could be an agamic complex. Breeding in this complex is possible due to the presence of diploid sexuals which can be treated by colchicine and pollinated by apomicts.     

Male fertility and cytology of triploid hybrids between tetraploidSolanum commersonii (2n=4x=48, 2EBN) and Phureja-Tuberosum haploid hybrids (2n=2x=24, 2EBN)

Summary Solanum commersonii Dun. is a diploid (2n=2x=24, 1EBN) wild species of potential value for potato breeding. It is a reproductively isolated species and cannot be crossed with Tuberosum haploids (2n=2x=24, 2EBN) or other diploid 2EBNSolanum species. In order to overcome the EBN barriers, triploid hybrids were produced between Phureja-Tuberosum haploid hybrids, which form 2n pollen grains by parallel spindles, and tetraploidS. commersonii. Microsporogenesis analysis of the triploids indicated a trend towards low values of chromosome distribution at Anaphase I; lagging chromosomes were often observed as well. Despite these abnormalities, the percentage of stainable pollen was very high, ranging from 5.0% to 74.3%. A high variation in pollen grain diameter was also evident. Parallel and tripolar orientation of spindles at Metaphase II of microsporogenesis was a common feature of all the triploids analyzed, but dyads and triads were observed at a very low frequency. Therefore, also the frequency of 2n pollen was very low; the different size of stainable pollen appears to represent the ploidy levels which are possible according to the distribution of chromosomes in Anaphase I. The results obtained also suggest thatS. commersonii could have minor genes acting at the end of meiosis in such a way that, despite the presence of parallel/tripolar spindles, dyads/triads are not formed.Contribution no. 124 from the Research Center for Vegetable Breeding.     

Introgression of crown rust resistance from diploid oat Avena strigosa into hexaploid cultivated oat A. sativa by two methods: direct crosses and through an initial 2x·4x synthetic hexaploid

New sources of resistance to crown rust, Puccinia coronata f. sp. avenae (Eriks.), the major fungal disease of cultivated oat, Avena sativa L. (2n = 6x = 42), are constantly needed due to frequent, rapid shifts in the virulence pattern of the pathogen. Crown rust resistance identified in the diploid oat A. strigosa (Schreb.) (2n = 2x = 14) accession CI6954SP was transferred into cultivated oat using two methods: direct cross of the diploid to a hexaploid cultivar facilitated by embryo rescue, and initial cross of the diploid to a wild tetraploid oat to make a synthetic hexaploid for subsequent crossing to a hexaploid cultivar. Two tetraploids, a crown rust resistant A. murphyi (Ladiz.) accession P12 and a susceptible A. insularis (Ladiz.) accession INS-1, were used in the 2x·4x crosses. Resistant backcross-derived lines were recovered by both methods. Although the 2x·4x synthetic method did not require the laborious discovery and rescue of an infrequent initial hybrid embryo of the direct cross, the direct cross method provided more rapid backcross recovery of plants with high fertility, full transmission of resistance, and desired plant and seed phenotypes. A suppressor effect, present initially but segregating in backcrosses, appeared to come from the CI6954SP donor and is the same as, or analogous to, suppression by an oat line with the crown rust resistance gene Pc38. No resistance from A. murphyi P12 was detected in advanced generations when it was introduced either as a component of a synthetic hexaploid or in direct crosses to A. sativa, indicating suppression of its resistance in interploidy combinations. That the dominant resistance gene transferred from CI6954SP and a gene Pc94 introgressed earlier from a different A. strigosa accession may be the same or quite similar to one another is indicated by their in-common specificity to suppression of resistance expression, susceptibility to a newly recovered rust isolate, and close linkage to the molecular marker SCAR94-2. The introgressed resistance genes from the different sources, even if the same, may have different cultivar genomic introgression sites, which would allow tests of dosage effects on resistance expression.     

Hybrids of <Emphasis Type="Italic">Avena sativa</Emphasis> with two diploid wild oats (CIav6956) and (CIav7233) resistant to crown rust

Two diploid accessions of wild oat, CIav6956 and CIav7233, were identified as carrying seedling resistance to oat crown rust (caused by Puccinia coronata f. sp. avenae; Pca). Two vigorous interploidy F₁ hybrids were generated from crosses involving the hexaploid oat cultivar Wintaroo and the diploid oat Avena strigosa Schreb. accession CIav6956. An additional interploidy F₁ hybrid, designated “F1-Aa1”, was produced from a cross of Wintaroo and the diploid oat accession CIav7233. All three hybrids were more vigorous and taller than the cultivated parent Wintaroo. The three F₁ hybrids contained full chromosome complements from both parents (2n = 4x = 28), but no seeds were obtained when the three F₁ hybrids were selfed. Meiotic analyses of the hybrids indicated that they exhibited a high degree of inter-genome and intra-genome pairing. Trivalent configurations were detected in 95–96% of meiotic cells and a minimum of three bivalents was present in all cells. An average chiasma frequency of 7.2–7.9 per cell was observed for the three F₁ hybrids. A fourth F₁ hybrid was subsequently generated from a cross between the diploid oat accession CIav7233 and Wintaroo. One octaploid (2n = 8x = 56) was generated from this hybrid and progeny were resistant to two Pca races. The chromosome number of the octaploid progeny varied between 51 and 54 chromosomes. Development of a chromosome addition line(s) with the crown rust resistance should be possible from these partial-octaploids.     

Occurrence of numerically unreduced (2n) gametes in Alstroemeria interspecific hybrids and their significance for sexual polyploidisation

The F1 hybrids of seven diploid Alstroemeria species (2n=2x=16) were investigated for the production of numerically unreduced (2n) gametes and their mode of origin. Based on a survey of 17 interspecific hybrid combinations,consisting of 119 genotypes, it was found that the F1 hybrids of Chilean-Brazilian species mostly produced first division restitution (FDR) 2n gametes. These F1 hybrids were self-pollinated in order to obtain F2 seeds, which was an indication that the F1 plants also produced 2neggs simultaneously. All the F2 progeny plants were typical allotetraploids, most of which formed 16 bivalents and a small proportion formed multivalents during metaphase I stages of meiosis. Through genomic in situ hybridisation (GISH) it was proved that multivalent formation in F2plants, derived from A. inodora ×A. pelegrina hybrid, was due to homoeologous recombination but not from reciprocal translocations. In order to test the segregation pattern of the recombinant chromosomes, an F3 population from one genotype, P6C49-6, was investigated. The recombinant chromosomes assorted independently from each other supporting the hypothesis that the segregation of chromosomes in ring quadrivalents did not behave like those in translocation heterozygotes. It was concluded that in allopolyploids of Alstroemeria,bilateral sexual polyploidisation could accomplish genetic recombination by both homoeologous crossing-over as well as through the assortment of chromosomes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genotypic control of chromosome pairing in amphiploids involving the cultivated oat Avena sativa L.

Summary A genotype of the diploid species Avena longiglumis (Cw 57) has been shown to modify the genetic control of diploid-like chromosome pairing in the cultivated oat, A. sativa (2n=6x=42) leading to increased homoeologous chromosome pairing in 4x hybrids between the two species (Rajhathy & Thomas, 1974). The Cw 57 genotype has a similar effect in increasing homoeologous chromosome pairing in amphiploids combining diploid and hexaploid genomes including associations between alien chromosomes and their corresponding pairs in hexaploid species. The effect of the Cw 57 genotype is probably in altering the specificity of chromosome pairing in the early stages of meiosis. The use of the Cw 57 genotype to induce homoeologous chromosome pairing as a technique for the transfer of desirable alien variation into the cultivated oat is discussed.     

Cytological and genetical studies on hybrids between sorghum almum parodi (2n=40) and some diploid (2n=20) species of sorghum

Hybridization between S. almum (2n=40) and diploid (2n=20) species of Sorghum resulted in plants with 2n=40 and 2n=30 chromosomes. As segregation for many characters occurred in the offspring of those with 2n=40, hybrids of this type provide a means of transferring genes from the diploid to the tetraploid species of Eu-sorghum. Segregations for some genes in the progeny of these hybrids revealed heterozygosity in S. almum which may indicate that one of the ancestors of S. almum was a variety of S. vulgare very similar to the commercial grain sorghum.The triploids were only slightly fertile and the chromosome numbers of plants resulting from backcrossing to S. almum ranged from 30 to 46. Some of the plants with the higher chromosome numbers were self-fertile and segregation for genes which were present in the original diploid and tetraploid parents were observed in their off-spring. Backcrossing the triploid to the diploid parent produced fertile plants with 2n=20 and it is possible that the triploids could be used to transfer genes from the tetraploid to the diploid species of Eu-sorghum.The chromosome pairing in the triploids was similar to that expected in an autotriploid, but some non-homologous pairing was detected which may be the result of duplication of some chromosomes or chromosome segments within the genome (n=10) of S. vulgare.     

Gene transfer from non-tuberous to tuberous Solanum species: Evidence from meiosis in hybrids

Summary The distant hybrids between non-tuberous Solanum species and tuberous S. pinnatisectum display little or no pairing in F1 and predominantly bivalent formation (preferential pairing) after chromosome doubling. In such a situation the question about the potential and extent of gene transfer from the non-tuberous parent to the tuberous one is relevant to potato breeding. This question was investigated by studying meiosis in triploid and hexaploid hybrids from crosses between diploid TV⁵ x tetraploid (S. etuberosum x S. pinnatisectum). TV⁵ is similar to S. verrucosum with cytoplasm of S. tuberosum. The following evidence was found for the desirable transfer of S. etuberosum genes to the tuberous species.The triploid F1 hybrids did not display the configurations 12 II+12 I expected if no gene exchange would take place between S. etuberosum and the tuberous species; however, a considerable number of multivalents per cell was observed in all plants studied.In the hexaploid F1 hybrids, obtained from the triploids through somatic doubling in vitro, 36 bivalents could reasonably be expected. Although bivalents were predominant (an overall average of 24.2 per cell) quite a few chromosomes were associated as multivalents in all plants investigated.It is concluded that in the hybrids studied a considerable amount of pairing and chiasma formation occurs between chromosomes of non-tuberous and those of tuberous Solanum species. This pairing affinity is larger than that found in 2x and 4x hybrids from S. etuberosum x S. pinnatisectum. Some hypotheses are put forward to explain this increased pairing affinity.     

Production of 27-, 28-, and 56-chromosome apomictic hybrid derivatives between pearl millet (2n=14) and Pennisetum squamulatum (2n=54)

Summary An interspecific hybridization program designed to transfer gene(s) controlling apomixis from Pennisetum squamulatum Fresen. (2n=6x=54) to induced tetraploid (2n=4x=28) cultivated pearl millet, Pennisetum americanum (L.) Leeke resulted in four offtype plants, two with 27 chromosomes and two with 28 chromosomes. These plants were found among 217 spaced plants established from open-pollinated seed of an apomictic 21-chromosome polyhaploid (2n=21) plant derived from an apomictic interspecific hybrid (2n=41) between tetraploid pearl millet and Pennisetum squamulatum. It appeared that a 21- (or 20-) chromosome unreduced egg from the apomictic polyhaploid united with a 7-chromosome pearl millet (2n=2x=14) gamete to produce a 28- (or 27-) chromosome offspring. Meiotic chromosome behavior was irregular averaging from 3.60 to 4.05 bivalents per microsporocyte in the 27- and 28-chromosome hybrids. The 27- or 28-chromosome hybrids, like the 21-chromosome female parent, shed no pollen, but set from 1.8 to 28 seed per panicle when allowed to outcross with pearl millet. Progeny of the 28-chromosome hybrids were uniform and identical to their respective female parents, indicating that apomixis had been effectively transferred through the egg. In addition, a 56-chromosome plant resulting from chromosome doubling of a 28-chromosome hybrid was identified. Pollen was 68 per cent stainable and the plant averaged 2.3 selfed seeds per panicle. Chromosomes of the 56-chromosome plant paired as bivalents (x=10.67) or associated in multivalents. Three to nine chromosomes remained unpaired at metaphase I. Multiple four-nucleate embryo sacs indicated the 56-chromosome hybrid was an obligate apomict. The production of 27-, 28-, and 56-chromosome hybrid derivatives were the results of interspecific hybridization, haploidization, fertilization of unreduced apomictic eggs, and spontaneous chromosome doubling. These mechanisms resulted in new unique genome combinations between x=7 and x=9 Pennisetum species.     

Aneuploids of perennial ryegrass (Lolium perenne)

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.     

The production of yellow-seeded Brassica napus (AACC) through crossing interspecific hybrids of B. campestris (AA) and B. carinata (BBCC) with B. napus

To transfer the genes for yellow seed coat from both genomes A and C to B. napus (AACC), the hexaploid of Brassica (AABBCC) was synthesised from reciprocal interspecific crosses between yellow-seeded B.campestris (AA) and B.carinata (BBCC). The hexaploid with 27 pairs of chromosomes was red-seeded which showed that genic interaction existed in the trigenomic plants for the colour of the seed coat. Hundreds of hybrid seeds were obtained from crosses between the red-seeded hexaploid and partial yellow or brown-seeded varieties of B. napus as pollen donor. The majority of the hybrid plants (AABCC) were self fertile with brown seeds. It appeared that the chromosomes of the B genome were excluded during the meiosis of the pentaploid and a high proportion of the genetically balanced AC gametes could be produced. The fertility of the F2 population was increased and even reached normal levels for some plants. Seventy-three plants with the yellow-seeded character were isolated from 2590 open-pollinated F2 plants, most with increased fertility. After two successive self-pollinations, 18 lines produced yellow seeds and no brown seeds segregated from these populations. The morphology of the novel yellow-seeded plants was basically towards B. napus. Esterase isoenzyme electrophoresis showed that the plants contained some of the genetic background of B. campestris, B. carinata and B. napus. Cytological analysis has shown that at least some yellow-seeded lines have the B.napus AACC genome composition with 38 chromosomes and normal meiotic pairing. This revised version was published online in July 2006 with corrections to the Cover Date.     

The production and behaviour of hexaploid hybrids between Hordeum vulgare and H. Bulbosum

Summary To produce hexaploid (or other polyploid) hybrids, diploid or tetraploid Hordeum vulgare was crossed with hexaploid or octoploid H. bulbosum, and perennial triploid hybrids between the two species were treated with colchicine. The crosses did not yield viable plants: seedset was low, the seed aborted and embryo culture was unsuccessful. The colchicine treatments geve rise to plants in which hexaploid chromosome numbers were observed. At the hexaploid level chromosomal instability occurred, resulting in chromosome elimination.The colchicine-treated triploid hybrids showed in the first years after the treatment better fertility after open flowering than untreated plants, but the level of fertility remained very low. The offspring consisted of haploid, diploid and approximately triploid plants like H. vulgare, tetraploid and approximately tetraploid plants like H. bulbosum, and plants with hybrid morphology and unstable chromosome number, which were highly sterile. Thus the crossing barrier between H. vulgare and H. bulbosum could not be broken down at higher ploidy level.     

The introgression of characters of the wild oat Avena magna (2n=4x=28) into the cultivated oat A. sativa (2n=6x=42)

Summary A study of derivatives from the hybrid Avena sativa × A. magna backcrossed to A. sativa clearly indicate that it is possible to introduce characters of the wild oat into the cultivated oat. Progeny with improved grain characters and crude protein content of the groat have been isolated and their use as breeding material is discussed.     

Meiosis in different F1-hybrids of Solanum acaule Bitt. x S. bulbocastanum Dun. and its bearing on genome relationship,fertility and breeding behaviour

Summary Meiosis was studied in some triploid, tetraploid and hexaploid F₁-hybrids from Solanum acaule x S. bulbocastanum and in a triploid F₁-hybrid from S. acaule x S. tuberosum-haploid.The only anomaly found was stickiness at metaphase I, the degree of which appeared to be related to the proportion of the S. bulbocastanum chromosomes in the hybrids. No stickiness occurred at pre- and post-metaphase stages.A clear allosyndetic pairing between chromosomes of the two S. acaule genomes was observed in all triploid and tetraploid hybrids. These genomes apparently are closely related and little differentiated. The triploids S. acaule x S. bulbocastanum had 0–1 trivalent per cell, whereas 2–5 trivalents per cell were observed in the triploid S. acaule x S. tuberosum-haploid. Therefore S. acaule is more closely related to S. tuberosum L. than to S. bulbocastanum. A small amount of pairing between S. acaule and S. bulbocastanum is apparent from the occurrence of multivalents in all hybrids.Hexaploid F₁'s (2n=72) showed a nearly complete homologous pairing of chromosomes (35.2 bivalents per cell) and generally a normal separation of chromosomes at anaphase: 36-36. This offers an explanation for their high fertility. Triploid F₁'s from S. acaule x S. bulbocastanum have a high frequency of univalents leading to irregular separation of chromosomes at anaphase and consequently to unbalanced gametes and extreme sterility. In the tetraploid F₁'s (2n=48) nearly complete bivalent pairing was observed, 50% expectedly being homologous and 50% homoeologous pairing. Separation of chromosomes at anaphase was generally normal 24-24. In spite of this normal behaviour and allowing for tight stickiness at metaphase the tetraploids are very sterile. A satisfactory explanation cannot yet be given.Selfing and intercrossing hexaploid F₁'s gives normal berry set and many seeds per berry. However crosses with S. tuberosum and even those with the fertile hexaploid hybrid from 8x-S. acaule x 4x-S. tuberosum are little successful: berry set is far below normal and the berries are either parthenocarpic or contain only one or two seeds. These rather unexpected results warrant further investigation. Large-scale selfings and intercrosses of triploid and tetraploid hybrids have not been successful as yet. Among the female gametes of tetraploid hybrids a few appeared to be functional in crosses with hexaploid hybrids and in those with S. bulbocastanum.     

The production of 2n pollen in rose

Based on the size differences found between haploid and diploid pollen produced by diploid and tetraploid rose cultivars, respectively, 2n 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 2n 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 2n 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 2n pollen formation, triads (containing a 2n microspore at one pole and two n microspores at the other) resulting from abnormal spindle geometry were frequently observed. The mode of 2n pollen formation is genetically equivalent to a First Division Restitution (FDR) mechanism. FDR 2n pollen transmits a high percentage of the heterozygosity from the diploid parent – 2n pollen producer-to the tetraploid offspring.     

Barriers to hybridization of Solanum bulbocastanum Dun. and S. Verrucosum Schlechtd. and structural hybridity in their F1 plants

Summary Results of reciprocal crosses between Solanum verrucosum (2n=2x=24) and S. bulbocastanum (2n=2x=24) are described in terms of pollen tube behaviour in styles, of berry and seed set, of fertility and of meiotic behaviour of the F₁ hybrids. Pollen tube growth of S. verrucosum is strongly inhibited in styles of S. bulbocastanum, whereas no inhibition is observed in the reciprocal cross. Therefore S. bulbocastanum x S. verrucosum fails to set berries or seeds, whereas the reciprocal cross produces both berries (54.4% berry set) and seeds (0.3 per berry). Only 14.6% of the seeds germinate. Both the diploid and corresponding tetraploid hybrid plants are vigorous, flower abundantly, have a rather regular meiosis (mainly rod bivalents), but show a high degree of cytoplasmic-genic male sterility. Crossability of the diploid hybrid plants is nil when used as pollen parents and near to zero when used as pistillate parents. The barriers to hybridization of the parent species (unilateral inhibition of pollen tube growth, somatoplastic sterility, cytoplasmic-genic male sterility and structural differences of the parental chromosomes) are discussed and methods are suggested to overcome these barriers.     

Interspecific hybridization in sexual diploid Allium senescens var. minor× apomictic tetraploid A. nutans and sexual diploid A. senescens var. minor× apomictic hexaploid A. senescens

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.     

陆地棉和野生斯特提棉种间异源六倍体的合成与性状鉴定

陆地棉(Gossypiumhirsutum)是世界上重要的栽培棉种,野生斯特提棉(G.sturtianum)含有陆地棉所缺乏的许多优质基因。本研究通过陆地棉和斯特提棉的远缘杂交和染色体加倍,获得了自交可育的后代植株,对其进行流式细胞倍性检测和花粉母细胞减数分裂观察,筛选出2株染色体组完整的异源六倍体植株。统计鉴定表明,六倍体和亲本及三倍体比较,叶形介于双亲之间,叶面积增大,保卫细胞中叶绿体数明显增多;远缘杂种与亲本在花的表型性状方面差异明显,六倍体的花粉粒直径大于亲本和三倍体;六倍体棉纤维为白色,长度小于母本陆地棉,父本斯特提棉的种子腺体延缓发育性状在异源六倍体中得到表达。这些结果证明通过远缘杂交和加倍成功获得了陆地棉与斯特提棉间可育的异源六倍体新种质,为棉花遗传育种研究提供了有价值的材料。