Bulb-type onion introgressants posessing Allium fistulosum L. genes recovered from interspecific hybrid backcrosses between A. cepa L. and A. fistulosum L.

Allium fistulosum possesses a number of traits which would be desirable in A. cepa. Thus far, no commercial A. cepa cultivars have been released which harbor Allium fistulosum traits. F₁BC₃ populations were generated for this study by backcrossing A. cepa to A. cepa×A. fistulosum hybrids. The F₁BC₃ plants were evaluated for plant morphology, floral characters, male- sterile cytoplasm, soluble solids and pungency, and isozymes. Overall growth habit and floral characters of the F₁BC₃ plants were much like A. cepa. We report here the recovery of recombinant, bulbing, and fertile A. cepa-type onions that exhibit A. fistulosum isozyme alleles and morphological markers. Recombination between A. cepa and A. fistulosum genomes was achieved using the introgression strategy of backcrossing A. fistulosum into A. cepa, thereby ameliorating the nuclear cytoplasmic barriers that occurred in previous less successful introgression attempts when plants were not in A. cepa cytoplasm. We believe this report to be the first demonstration of onion introgressants that are like A. cepa in appearance, are male- and female-fertile, and possess A. fistulosum genes. Received: 29 May 1999 / Accepted 22 June 1999     

Interspecific hybrid between Allium cepa and Allium sativum

Summary Interspecific hybrids between Allium cepa and Allium sativum were obtained using the fertile clone A. sativum as the male parent. The nascent embryos which formed shortly in interspecific hybridization between A. cepa and A. sativum were rescued by ovule culture at an early stage. The zygotes or proembryos developed in Murashige and Skoog medium containing 5.7×10^-8 M indole-3-butyric acid (IBA). Once developed, the embryos were taken out of the ovule and cultured on embryo culture medium where they regenerated into whole plants. The hybridity of the plants obtained was examined by morphological observation, chromosome analysis, and ribosomal RNA gene analysis. The analyses proved that the plants were mature sexual hybrids between A. cepa and A. sativum. Each hybrid plant had keeled but fistulose leaves and formed a bulb resembling that of A. cepa. The hybrids produced not only S-propenyl-l-cysteine sulfoxide, which is the major flavor precursor in A. cepa, but also S-allyl-l-cysteine sulfoxide (alliin), which is characteristic of A. sativum.     

Synaptonemal complex spreading in Allium cepa and A. fistulosum

The general features and fine structure of homologous chromosome alignment and pairing have been investigated in two species of Allium (A. fistulosum and A. cepa), which have similar karyotypes but very different patterns of chiasma distribution. Although there is no support for the occurrence of a general pre-meiotic alignment of homologous chromosomes, both species show some alignment of homologues as an immediate prelude to synaptonemal complex (SC) formation. In both species pairing usually commences at sub-terminal sites and is succeeded by numerous separate intercalary initiations of pairing in interstitial and distal regions and then in proximal regions. The last parts to pair, in both species, are pericentromeric and telomeric regions. There is, therefore, no evident relationship between the sequence of pairing and chiasma distribution in these species. Regularly alternating convergences and divergences of aligned axial cores (ACs), termed multiple association sites, are frequently observed. It is proposed that these represent potential pairing initiation sites and from observations on their spatial distribution it is argued that they may be evenly distributed through most of the genome. Small spherical or ellipsoid nodules are found at association sites and between closely aligned ACs which persist in the SC segments present during zygotene, but most of them disappear abruptly at the end of zygotene. These are termed zygotene nodules (ZN) and it is proposed that they are involved in matching corresponding sites on homologous chromosomes as well as possibly having a recombinational role. Their composition, structure, mode of action and relationship to pachytene recombination nodules are at present unknown.     

Recombinant chromosomes of advanced backcross plants between Allium cepa L. and A. fistulosum L. revealed by in situ hybridization

Cytological analysis of (Allium cepa L.×Allium fistulosum L.)×A. cepa L. F₁BC₃ plants revealed most plants were diploid with 16 chromosomes. Karyotypes of these plants showed recombinant chromosomes. Fluorescence and genomic in situ hybridization patterns of interspecific F₁ hybrid and F₁BC₃ plants revealed A. fistulosum chromosomes or chromosomal segments. A highly repetitive 376-bp DNA sequence and genomic DNA of A. fistulosum revealed similar telomeric hybridization sites when hybridized onto A. fistulosum chromosomes. Cytogenetic evidence showed that A. fistulosum DNA has recombined into the A. cepa genome. Received: 20 October 1999 / Accepted: 11 November 1999     

Central cell nuclear-cytoplasmic incongruity:a mechanism for segregation distortion in advanced backcross and selfed generations of (Allium cepa L. x Allium fistulosum L.) x A. cepa interspecific hybrid derivatives

A model is presented as an explanation for an anomaly observed in germination and establishment and isozyme segregation patterns in Allium cepa x A. fistulosum F2BC3 populations generated in an introgression-breeding program. The F1BC3 parent of these populations was selected for its heterozygous PGI phenotype, Pgi-1(2/3); Pgi-1(2) was inherited from an A. cepa (Ac) seed parent and Pgi-1(3) from an A. fistulosum (Af) pollen parent. Germination and establishment was recorded for the F2BC3 progeny population. Segregation of Ac and Af Pgi-1 alleles was investigated in F2BC3 seeds and embryo and endosperm tissue was isolated and tested for isozyme expression. A pooled goodness-of-fit test of the segregation of Pgi-1 alleles in the populations to the expected Mendelian 1:2:1 ratio using the chi-square statistic gave a chi2 = 185.9, well beyond the accepted limits at 2 degrees of freedom. The 1:2:1 ratio expected for simple Mendelian inheritance was rejected, while a pooled chi-square goodness-of-fit test of the segregation of Pgi-1 alleles in the populations fit a 1:1 ratio with a chi2 = 0.203, based on the incongruity model. We present here the central cell nuclear-cytoplasmic incongruity hypothesis to explain the observed anomalies.     

Introgression of Allium fistulosum into A. cepa mediated by A. roylei

Introgression of Allium fistulosum into the genome of A. cepa using A. roylei as a bridging species was studied by means of genomic in situ hybridization (GISH). Here we demonstrate for the first time that A. fistulosum can be stably introgressed into A. cepa with a bridge-cross. The first and second bridge-cross generations were fertile, although pollen was sterile in some individuals. Only occasionally were there translocations in the second generation bridge-cross. Recombination between the three genomes was frequently seen in meiotic anaphase 1 and prophase 2 chromosomes of the first generation bridge cross and in mitotic chromosomes of the second generation bridge-cross. The number of observed recombination points in anaphase 1 and prophase 2 significantly exceeded the value expected from chiasma frequency in metaphase 1. Recombination points were randomly distributed, thus the A. cepa or A. roylei type of random distribution prevails over the A. fistulosum type of proximally localised chiasmata. Received: 15 December 1998 / Accepted: 18 February 1999     

Introgression of Allium fistulosum L. into Allium cepa L.: cytogenetic evidence

Summary A diploid Allium cepa plant was recovered from the backcross of an interspecific triploid (2 x A. cepa + 1 x A. fistulosum) to an A. cepa diploid which exhibited both A. cepa and A. fistulosum Adh-1 alleles. Cytogenetic analyses revealed a recombinant sub-telocentric chromosome. The ADH-1 locus is believed to be on the long arm of the sub-telocentric A. fistulosum chromosome 5. Meiosis of the triploid progenitor gives strong evidence that recombination occurred. A. fistulosum chromosome 8 has been substituted for A. cepa chromosome 1.Contribution of the College of Agricultural Sciences, Texas Tech University, Journal No. T-4-275     

Production of interspecific hybrids between Allium fistulosum L. and A. macrostemon Bunge through ovary culture

Interspecific hybridization is an effective method to generate a new crop in a short time that exhibits available traits. Nine interspecific hybrids between Allium fistulosum and A. macrostemon were produced through reciprocal crossings by ovary culture. This is the first report of hybrid development in the cross-combination. When A. macrostemon, a vegetative propagated plant, was used as the mother plant, no hybrid was obtained, but it was obtained by removal of bulbils and separation of the flower stalk, as with cut flowers. Ovary culture was performed on phytohormone-free B5 medium modified by Dunstan and Short (BDS) medium containing 30 g l⁻¹ sucrose 7 days after pollination. Germinated embryos were transferred to BDS medium containing 1 mg l⁻¹ 6-benzylaminopurine and 15 g l⁻¹ sucrose for 21 days. The plantlets were subcultured on phytohormone-free B5 medium for subsequent rooting. Hybridity was confirmed using cleaved amplified polymorphic sequence analysis of the rDNA internal transcribed spacer region and chromosome observation. In addition, the hybrids showed intermediate traits: they had fistulous leaves like those of A. fistulosum and bulbs like those of A. macrostemon. They displayed vigorous growth and propagated vegetatively by tillering. These results show the important discovery that vegetatively propagated plants are useful for cross breeding.     

Interspecific hybrids between onion (Allium cepa L.) with S-cytoplasm and leek (Allium ampeloprasum L.)

 Interspecific hybrids between Allium cepa and A. ampeloprasum have been generated as a first step for the introduction of S-cytoplasm from onion into leek. Pre-zygotic barriers of crossability were observed after the arrival of pollen tubes at the end of the style when entering the cavity. Nevertheless, micropyle penetration of pollen tubes and the formation of hybrid embryos were also observed. After accomplishing in vitro culture of ovaries and ovules successively, triploid hybrid plants with 24 chromosomes were obtained. Their hybrid nature was confirmed by RAPD analysis, genomic in situ hybridization, and morphological analysis. Southern hybridization with a cytoplasmic probe indicated the transfer of unaltered S-cytoplasm into the hybrid plants. Received: 9 May 1996 / Accepted: 23 August 1996     

胡葱与洋葱、葱过氧化物酶同工酶研究及聚类分析

本文对胡葱与洋葱、葱的功能叶过氧化物酶同工酶电泳图谱分析和聚类分析表明：这三个种及葱的3个交种闻的亲缘关系被区分开来;胡葱与洋葱的亲缘关系比胡葱与大葱的亲缘关系更近。     

Comparison of the Giemsa C-Band karyotypes and the relationships of Allium cepa,A. fistulosum and A. galanthum

Giemsa C-band staining of somatic chromosomes in Allium cepa, A. cepa cv. Shallot, A. fistulosum and A. galanthum shows that these four taxa are characterised by all chromosomes having one band at each telomere, except chromosome arms with satellites, in which case the band is proximal to the nucleolar constriction. This similarity is correlated with common morphological characteristics and an ability of the three species to hybridize with one another, indicating that they have a close genetic relationship. The results indicate that Giemsa C-bands are evolutionarily conservative in this group and provide a useful criterion for determining relationships.     

GISH study of advanced generation of the interspecific hybrids between Allium cepa L. and Allium fistulosum L. with relative resistance to downy mildew

Genomic in situ hybridization (GISH) was used for a chromosomal composition study of the later generations of interspecific hybrids between A. cepa L. and A. fistulosum L., which are relatively resistant to downy mildew (peronosporosis). GISH revealed that F₂ hybrids, which did not produce seeds, were triploids (2n = 3x = 24) with 24 chromosomes and possessed in their complements 16 chromosomes of A. fistulosum L. and eight chromosomes of A. cepa L. or eight chromosomes of A. fistulosum L. and 16 chromosomes of A. cepa L. The advanced F₅ hybrid, which produced few seeds, was amphidiploid with 32 chromosomes. BC₁F₅ hybrid was triploid with eight chromosomes of A. fistulosum L. and 16 chromosomes of A. cepa L., which did not produce seeds. BC₂ (BC₁F₅) plant was amphidiploid that possessed 4 recombinant chromosomes and produced few seeds. GISH results point to 2n-gametes formation in macro- and microsporogenesis of the hybrids. The mechanism of 2n-gametes formation and the possibility of apomixes events in the backcrossing progeny are discussed.     

Production and characterization of somatic hybrid plants between leek (Allium ampeloprasum L.) and onion (Allium cepa L.)

 Results are reported on the production and characterization of somatic hybrids between Allium ampeloprasum and A. cepa. Both symmetric and asymmetric protoplast fusions were carried out using a polyethylene-based mass fusion protocol. Asymmetric fusions were performed using gamma ray-treated donor protoplasts of A. cepa and iodoacetamide-treated A. ampeloprasum protoplasts. However, the use of gamma irradiation to eliminate or inactivate the donor DNA of A. cepa proved to be detrimental to the development of fusion calli, and thus it was not possible to obtain hybrids from asymmetric fusions. The symmetric fusions yielded a high number of hybrid calli and regenerated plants. The analysis of the nuclear DNA composition using interspecific variation of rDNA revealed that most of the regenerated plants were hybrids. Flow cytometric analysis of nuclear DNA showed that these hybrid plants contained a lower DNA content than the sum of the DNA amounts of the parental species, suggesting that they were aneuploid. A shortage of chromosomes in the hybrids was confirmed by genomic in situ hybridization. Chromosome counts in metaphase cells of six hybrids revealed that these plants lacked 2–7 leek chromosomes. One hybrid showed also the loss of onion chromosomes. The hybrids had an intermediate phenotype in leaf morphology. The application of these somatic hybrids in breeding is discussed. Received: 7 April 1997 / Accepted: 10 September 1997     

Micronuclei frequency and character coherence inAvena sativa L./A.fatua L. crosses

Summary The use of micronuclei frequency per microspore quartet (MF) has been proposed to indicate the relative reduction in chromosome homology among interspecific oat (Avena L.) hybrids. Hybrids with lower MF would presumably undergo greater genetic recombination, providing greater opportunity for breaking linkages that contribute to association, or coherence, of desirable and undesirable characters in progenies. Microspore quartets from 63A. sativa/A. fatua hybrids were observed. Character coherence was examined in progenies of the four hybrids with the highest MF (2.22 to 2.82 micronuclei/quartet) and four hybrids with the lowest MF (0.23 to 0.31 micronuclei/quartet) to determine whether a relationship existed between MF and character coherence. Coherence of seed disarticulation with quantitative characters that differentiate the parental species was more frequent in high MF crosses as was expected if high MF is indicative of reduced recombination. However, incidence of coherence between seed color and the quantitative characters was not related to MF differences among the crosses. Likewise, the degree of coherence among the quantitative characters, as measured by coefficients of concordance, was not associated with differences in MF among the crosses. Thus, coherence of the characters studied was not associated consistently with differences in MF.     

A relationship between callose and ectodesmata in epidermal cells of Allium cepa L.

Summary The outer wall of adaxial epidermal cells of onion bulb scales shows punctate callose deposits. The abundance of these callose deposits is highly variable, and seems to correlate with the distribution of ectodesmata. It is proposed that callose is involved in the regulation of ectodesmata as a waterflow regulator and/or molecular filter, thus influencing the cell-environment interaction.Abbreviations LS Linsmaier-Bednar and Skoog - 2,4-D 2,4-ichlorophenoxy-acetic acid - HRGP Hydroxy-proline rich glycoproteins     

Chromosome characteristics and behavior differences in Allium fistulosum L., A. cepa L,their F1 hybrid,and selected backcross progeny

Mitotic and meiotic studies were performed on Allium fistulosum, A. cepa, their F₁ hybrid, and ten selected backcross (BC)₁ plants [(A. fistulosum x A. cepa) x (A. cepa)]. Each BC₁ plant had at least one A. cepa isozyme allele (Pgi, Idh, or Adh). Chromosome morphology and behavior differed among plants. Meiocytes were observed with one, two, or three bridges and/ or fragments, indicating at least three paracentric inversions between A. fistulosum and A. cepa. Unusual crossing over and multivalent associations suggest that the 5F subtelocentric chromosome of A. fistulosum is involved in at least one translocation. The number of bridges and fragments and multivalent associations varied between the F₁ hybrid and BC₁ progenies. The F₁ hybrid and all BC₁ progenies were either sterile or had very little seed set. Fertility was not restored in any of the selected BC₁ plants.The use of trade names does not imply endorsement of the products named nor criticism of similar ones not named. This research was supported by the New Mexico Agricultural Experiment Station     

Microtubule Cycle in Root Tip Cells of Allium fistulosum L.

Using immunofluorescent localization techniques and TEM methods, the organization of microtubule arrays during the cell cycle of root tip cells of Allium fistulosum L. was studied. There are four basic types of microtubule organization, namely, interphase cortical microtubule, pre-prophase band microtubule, spindle microtubule and phragmoplast microtubule, which constitute the typical microtubule cycle in dividing cells of higher plants. The fluorescent figures of microtubules observed under fluorescent microscope were explained and analysed by the ultrastractural informations of microtubules obtained from TEM.