Tracing of 2n egg occurrence in perennial ryegrass (Lolium perenne L.) using interploidy crosses

Several genotypes of Lolium perenne (2n = 2x = 14) were screenedfor the production of 2n eggs. In each cross a diploid genotype, used asfemale parent, was pollinated with a tetraploid genotype. All interploidycrosses were made in isolation cages. Flow cytometrical analysis of theprogeny of 154 diploid plants revealed 28 tetraploid descendants. Theseoffspring plants were harvested on 15 different diploid mother plants.Amplified Fragment Length Polymorphism (AFLP) markers were used tocheck the parenthood of these tetraploids. Two seedlings died, theremaining plants could, after AFLP fingerprinting, be identified as meiotictetraploids. The results obtained allowed to conclude that the tetraploidprogeny plants harvested on 15 diploid mother plants were the result ofthe fertilisation of an unreduced egg by a reduced pollen grain of thetetraploid plant.     

Flow cytometric identification of sexually derived polyploids in hop (Humulus lupulus L.) and their use in hop breeding

The New Zealand hop breeding programme is based solely on the development of seedless triploid cultivars. This relies on the use of tetraploid parents. While a sexually derived tetraploid parents have been used successfully, sexually derived tetraploids offer a useful alternative. They may have a higher level of heterozygosity and are easier to obtain. Methods for the identification of tetraploids from seedling populations by flow cytometry are described. Two studies were conducted; one on field-grown plants, the other on plants grown in a glasshouse. Approximately 15%of seedlings in the two studies were identified as tetraploids (2n = 4x = 40). Between 70 and 80% were identified as either diploid (2n =2x = 20) or triploid (2n = 3x = 30). Remaining plants were haploid, pentaploid or probably aneuploid. Within triploid and tetraploid populations from 40to 50% of seedlings were female, 30 to40% were monoecious, with the remainder being males and non-flowering plants. Sexually derived tetraploid parents have been used successfully in the breeding programme, from which several promising triploid selections have subsequently been made. This revised version was published online in July 2006 with corrections to the Cover Date.     

Bilateral polyploidization inDactylis glomerata L. subsp.lusitanica: occurrence,morphological and genetic characteristics of first polyploids

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.     

Crosses between Beta intermedia bunge and B. vulgaris L.

Summary A tetraploid annual male sterile form of Beta vulgaris L. (2n=4x=36) was crossed with the wild beet species Beta intermedia Bunge (2n=36). The resulting F₁-plants were male sterile annuals being two or three times back-crossed to diploid and tetraploid sugar and fodder beets in the next years. Apart from tetraploid material (36 chromosomes) hexaploid (54 chromosomes) and a number of aneuploid plants developed.The results obtained justify the conclusion that, at a tetraploid level the material mostly propagates apomictically after the F₁ generation. The presence of penta-, hexa-, septa-and even octaploid plants might be explained by assuming that no meiosis has taken place in the crossing partners. Triploid plants are sometimes found in the progeny of hexaploid material and may presumably be considered haploids. Moreover some pentaploid plants were found in the progeny of the open pollinated F₁ which after two generations of bagging are still pentaploids although they produce no pollen. This is another clear indication of apomictic reproduction.The tetraploid generation from the cross between the hexaploid material and diploid sugar beets probably contains the best prospects for breeding.     

Cytogeography and variation of stomatal size of Paspalum Glaucescens (Gramineae; Paniceae) in Southern Brazil

Paspalum glaucescens belongs to the informal group Plicatula, reproductively characterized by the dominance of tetraploid apomitic lines in most of its populations, with rare diploid, sexual counterparts. The species shows high phenotypic variation. Twenty nine Southern Brazilian accessions were cytologically and morphologically analysed. Most of the accessions were tetraploid (2n = 4x = 40). Meiotic study of three tetraploids showed their irregular behaviour. Eight accessions presented the diploid level (2n = 2x = 20).This can be considered a very high frequency of diploids in a member of the Plicatula group. While the tetraploids are concentrated at the highest elevations, diploids were detected mostly in the lowlands. Average stomatal sizes were quite distinct on different ploidy levels, being larger in tetraploids. This revised version was published online in July 2006 with corrections to the Cover Date.     

Amphidiploids between Cyclamen persicum Mill. and C. purpurascens Mill. induced by treating ovules with colchicine in vitro and sesquidiploids between the amphidiploid and the parental species induced by conventional crosses

Summary We cultured colchicine-treated hybrid ovules in vitro to produce fertile amphidiploids of C. persicum (2n=2x=48. referred to as AA) × C. purpurascens (2n=2x=34, referred to as BB). Seedlings and mature plants were obtained from the ovules without colchicine and those exposed to 50 mg/l colchicine for 5, 10 and 15 days, whereas they were not obtained from the ovules exposed to 50 mg/l colchicine for 20 days and 500 mg/l for 5, 10, 15 and 20 days. Although 8 mature hybrids derived from the ovules without colchicine produced a few fertile pollen grains, they failed to produce viable seeds by self-fertilization. The hybrids had 41 somatic chromosomes. Four and 3 mature plants were derived from ovules exposed to 50 mg/l colchicine for 10 and 15 days, respectively. One each among 4 and 3 mature plants showed a high frequency of pollen grain fertility, produced several seeds by self-fertilization, and had 82 somatic chromosomes which is twice the number of hybrid chromosomes (2n=41, AB). These findings indicated that these plants are amphidiploids (2n=82, AABB) between C. persicum and C. purpurascens. Three and 2 viable seeds were derived by the conventional crosses of diploid C. persicum × the amphidiploid and the amphidiploid × C. purpurascens, respectively. Flowering plants that developed from the seeds of diploid C. persicum × the amphidiploid were barely fertile and had 65 somatic chromosomes (2n=65, AAB), whereas those that developed from the seeds of the amphidiploid × C. purpurascens were barely fertile and had 58 somatic chromosomes (2n=58, ABB). The somatic chromosomes indicated that these plants are probably sesquidiploids between the amphidiploid and either C. persicum or C. purpurascens. The interspecific cross-breeding of cyclamen using the amphidiploids and the sesquidiploids is discussed.     

Bilateral sexual polyploidization in potatoes

Summary Bilateral sexual tetraploidization was achieved by intercrossing diploid Phureja × haploid Tuberosum hybrids. Both parents contribute gametes with the somatic number of chromosomes (diplogynoids and diplandroids). More than 100 tetraploid progeny appeared in nine 2x–2x families. The tetraploids are generally more vigorous and significantly outyield their diploid full-sibs. The superiority of the tetraploids is interpreted on the basis of the mode of diplandroid (2n pollen) formation by first meiotic division restitution (FDR). Heterozygosis, epistasis and genetic diversity, if present in the parental diploid genotype, are largely maintained in the 2n gametes formed by FDR. and syngamy brings about more opportunities for heterotic responses in conjunction with polyploidization. Differences in tuber yield among tetraploid clones within families were found to be statistically significant (P <0.05). Thus, unlike somatic chromosome doubling, which can merely increase chromosome numbers, or somatic hybridization, which could in addition bring about heterosis, sexual polyploidization is also associated with genetic variability. The degree of inbreeding and the genotypic structure in the population of newly arisen tetraploids is discussed. The relationship among asexual reproduction, preservation of favorable nonadditive genetic effects by FDR. restoration of sexuality, and polyploidization is explored. The possible evolutionary significance of these factors is emphasized.     

Polyploidy in tulips (Tulipa L.). The occurrence of diploid gametes

Summary From data available in the literature and supplemented by information from private tulip breeders, it appeared that triploid and tetraploid varieties raised in the past, resulted from crosses between diploid tulips and between diploids and tetraploids. This can only be explained by the occurrence of diploid gametes in diploid (2n=24) cultivars. This phenomenon which may affect both female and male gametes, appears to be specific for certain varieties. Consequences for practical breeding are discussed.     

Cytogenetic variation in somatic tissue cultures and regenerated plants of barley (Hordeum vulgare L.)

Summary Chromosome number of morphogenic and non-morphogenic calli and regenerated plants of barley were determined. Cultures were obtained from two kinds of explants, immature embryos and seedling leaves from three cultivars, Ingrid, Dissa and Golden Promise. Callus chromosome analyses were carried out during a 12 month period in a medium containing 2 mg/l of 2,4-D. Diploid cells were predominant in all cases; although in leaf-derived cultures, retraploid cells (2n=4x=28) showed a tendency to increase as time in culture increased and after more than six months in culture, diploid cells decreased to percentages of almost 70%. Aneuploid cells were generally infrequent in all cases. The source of explant has been more important than the genotype (cultivar) and the type of callus (morphogenic vs. non-morphogenic) in the chromosomal stability of cultures as time increases. From short term cultures, only 1.85% of the regenerated plants were tetraploid, the remaining were diploids. The ability of morphogenic calli to regenerate plants decreased before any significant reduction of diploid cells were observed.     

甘蓝型油菜三体、双三体和双四体的形态和细胞学特征

从甘蓝型油菜品种“Oro”×诸葛菜杂交后的一个混倍体杂种（2n=19~37）的小孢子再生植株中鉴定出一株2n=42的植株，此混倍体不含有诸葛菜染色体，故2n=42植株的细胞内没有诸葛菜染色体。用其花粉授予“Oro”后获得2n=39、40的植株。2n=39、40、42植株PMCs内染色体的主要配对方式分别为19Ⅱ+1Ⅰ、19Ⅱ+2Ⅰ和19Ⅱ＋2Ⅱ，后期Ⅰ的分离方式分别为20∶19、21∶19和21∶21。故2n=39、40、42为甘蓝型油菜的三体、双三体、双四体。最后讨论了这些种内非整倍体材料在油菜遗传研究中的意义。     

Note on the probable cause of the occurrence of tetraploid plants in commercial triploid varieties of sugar beet

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.     

Analysis of parental effects on mean vine maturity and chip colour of 4x.2x potato progenies

Summary The parental effects on progenies from potato 4x.2x(FDR) crosses were analyzed to determine anether and to what extent selection criteria used for selecting tetraploid breeding lines have to be adjusted when selecting diploid breeding lines. For vine maturity and chip colour multiple regression analysis of progeny means on means of diploid and tetraploid parents revealed high coefficients of determination (R²) for both characters, indicating good predicting power of the performance of both diploid and tetraploid parents on the performance of their 4x.2x progenies. For vine maturity the multiple regression slope for the tetraploid perents was significantly larger than for the diploid parents, and progeny means were towards the tetraploid parents. This indicates that selection criteria for vine maturity may be less stringent at the diploid level. However, diploids may be earlier maturing than tetraploids and therefore selection criteria can better be similar at both ploidy levels. For chip colour, multiple regression slopes for diploid and tetraploid parents were similar and progeny means were towards the darkest coloured parent irrespective of its ploidy level. This indicates that selection of breeding lines for chip colour can be conducted similarly at both ploidy levels.     

Analyses of phenotype and ARGOS and ASY1 expression in a ploidy Chinese cabbage series derived from one haploid

The aim of this research was to improve our understanding of how ploidy level influences phenotype and gene expression in Chinese cabbage (Brassica rapa L. ssp. pekinensis). Haploid plants (2n = 10) was induced by 0.2% colchicine to produce diploid (2n = 20) and tetraploid plants (2n = 40). The aneuploid (2n = 24) was also obtained by hybridization between diploid plants as the female and tetraploid plants. The ploidy levels of all plants were identified through chromosome counts and flow cytometry. Leaves and petals became larger as the ploidy level increased from haploid to diploid, and from aneuploid to tetraploid. Similarly, expression of ARGOS was regulated by genome size, increasing in parallel with the level of ploidy. Among the four ploidy types, expression was stronger in the floral buds than in the leaves. Expression by ASY1 also differed according to ploidy level, being highest in diploid plants, followed in order by tetraploids. Expression was similar between haploids and aneuploids at two stages—prior to and after meiosis—but was higher in the haploids during meiosis. When buds were compared within the same ploidy type at different stages, ASY1 expression was obviously higher during meiosis than either before or after. Our study demonstrated the generation and phenotype of a ploidy Chinese cabbage series derived from one haploid. Expression of genes ARGOS and ASY1 were modulated by genome size in this ploidy series, and the regulated patterns of the two genes was different.     

Intergeneric crosses with Fragaria and Potentilla. I. Crosses between Fragaria moschata and Potentilla fruticosa

Summary Crosses between Fragaria moschata (2n=42) and Potentilla fruticosa (2n=14) produced many seeds; about half of these germinated, but only nine plants were obtained from 554 seedlings. Five plants died without flowering, and four were vigorous but sterile. Four plants had the expected chromosome number (2n=28), one plant had 21 chromosomes, and four were aneuploid with 23, 24, 25 and 27 chromosomes respectively. Response to growth substances giving elongated stem internodes and swollen but not succulent receptacles provided evidence that two of the plant were hybrids. It is suggested that all nine plants originated from a normal fertilisation which was followed in some cases by chromosome elimination at an early stage of embryo development.     

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.     

Isozyme variation between diploid and tetraploid cytotypes of Glycine tabacina (Labill.) Benth.

Summary Glycine tabacina (Labill.) Benth. is a wild perennial species related to the cultivated soybean, G. max (L.) Merr. It is composed of diploid (2n=40) and tetraploid (2n=80) cytotypes. Currently, to differentiate the cytotypes, plants are grown out in the greenhouse and chromosome counts made on pollen mother cells. It is a laborious and time consuming process. The objective of this study was to determine whether electrophoretic techniques could be utilized to separate the cytotypes. Electrophoretic examination of seven isozyme systems from seed of 67 G. tabacina accessions revealed banding patterns that could be used to differentiate between diploid and tetraploid cytotypes in the species. Among the tetraploid accessions, the number of bands observed were always greater than the diploids. Some tetraploid banding patterns consisted of bands similar to the diploid tabacina and/or additional bands previously identified in other Glycine species. The patterns of isozyme multiplicity and variation in the tetraploid tabacinas suggests more than one mode of origin for the tetraploids.     

Production of intraspecific aneuploids in the genus Solanum. 1. Doubling the chromosome number of seven diploid species

Summary The variation which persisted in interspecific aneuploids even after one or two generations of backcrossing prevented the morphological distinction of the aneuploids from their diploid sibs. An attempt was made to unmask the effects of aneuploidy by producing aneuploids within the more uniform genetic background of a single species.The procedure to produce trisomics and aneuploids of diploid species was to vegetatively double clones or seed of the species with colchicine, cross the induced tetraploids to diploids to produce triploids, and then cross the triploids to the original diploids. An attempt was made to use the same diploid clone and/or introduction of a species in all successive stages of the procedure in order to obtain as much uniformity as possible. This was largely unsuccessful because self-incompatibility and inbreeding reduced seed set. Seventy-three different tetraploids were obtained from seven species. Tuber treatments were noticeably unsuccessful in producing doubled plants. The two vegetative treatments were most successful and produced 41 different tetraploid clones while 30 doubled plants were obtained from four seed treatments.Morphologically the tetraploids resembled the diploid and there was no noticeable increase in size of leaflets and floral parts in the tetraploid. The average number of chloroplasts in ten pairs of guard cells was a distinctive feature which could efficiently be used in distinguishing the induced tetraploid plants from diploids. The tetraploids were generally less fertile than their diploid counterparts and the majority of them exhibited self-compatibility in comparison to self incompatibility of the diploids.Cooperative investigations of the Agricultural Research Service, U.S. Department of Agriculture and the Wisconsin Agricultural Experiment Station. Supported in part by grants from the Research Committee of the Graduate School, University of Wisconsin.     

Karyotypic and electrophoretic studies on taro and its origin

Summary Karyotypes and electrophoretic pattern of 15 strains of taro were studied. Strains collected from the northeast India hill state, Meghalaya were diploids and triploids whereas those from the plains of south India were diploids and of north India was a triploid. The diploids had 2n=28 and triploids showed 2n=42 chromosomes. The wild taro had the most asymmetrical karyotype. The protein content varied from 4.2 to 11.4 mg/g dry wt. The maximum protein content was found in a triploid strain 8 (11.4 mg/g dry wt) and minimum in the wild taro (4.2 mg/g dry wt). The number of protein bands was 7 in the wild taro (diploid) and 12 in one of the cultivated triploid strain. Meghalaya strains showed great variation with respect to leaf size and tuber shape and size. All the strains have diverged at morphological, karyotypic and genotypic levels. It is suggested that taro might have originated in the north-eastern India.     

Identification of tetraploid regenerants from cotyledons of diploid watermelon cultured in vitro

Summary Adventitious shoots were obtained from the diploid watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] cultivars Dixielee, Jubilee II, Mickylee, Minilee, and Royal Sweet by culturing excised cotyledons on shoot regeneration medium for six weeks. Tetraploid and diploid regenerants were identified by counting the number of chloroplasts per guard cell pair from leaves of regenerated plants. Cross fertilization of putative tetraploids with diploid pollinators and the production of triploid seed confirmed the efficacy of this approach. The mean number of chloroplasts for tetraploid regenerants was 19.1 whereas diploids averaged 11.2. These values were similar to tetraploid and diploid plants from seed. Ovary diameter, petal, and anther diameter of male flowers, and leaf length by width ratio were also good indicators of plant ploidy. Progeny obtained from self-fertile tetraploids of Mickylee were crossed with various diploid pollinators to produce triploid hybrid seed. All triploid plants from tissue culture-derived tetraploids produced fruit comparable in quality to fruit produced by currently-available triploid hybrids, demonstrating that in vitro tetraploid induction can be used to produce high quality tetraploid plants for use in triploid hybrid seed production.     

Somatic hybrids between navel orange (Citrus sinensis) and grapefruit (C. paradisi) for seedless triploid breeding

Protoplasts from cell suspension cultures of ‘Bonnaza’ navel orange (Citrus sinensis (L.) Osbeck) were electrically fused with mesophyll protoplasts isolated from seedless ‘Red Blush’ grapefruit (Citrusparadisi). After 6 months of culture, a total of 20 plants were regenerated. Root tip chromosome counting revealed that 4 of them were tetraploids (2n = 4x = 36)and the rest were diploids (2n = 2x = 18) morphologically resembling the mesophyll parent. After 6 months of transplantation into the greenhouse, 4 of the diploidmesophyll regenerants unexpectedly flowered, but this phenomenon disappeared in the next year. This is the first report of precocious flowering in citrus via protoplast fusion. RAPD analysis further confirmed that the tetraploid regenerants were somatic hybrids while the diploid regenerants were mesophyll parent type. This somatic hybrid will be utilized as a possible pollen parent for improving the seedy pummelo cultivars in China by producing triploid seedless pummelo hybrid. The mechanism of early flowering was also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.