The causes and consequences of meiotic irregularity in the leek (Allium ampeloprasum spp. porrum); implications for fertility, quality and uniformity

We have previously confirmed that Allium ampeloprasum spp. porrum, the leek, shows extensive and frequent quadrivalent formation during prophase I of meiosis, and that despite the resolution of most of these into bivalents some quadrivalents persist to metaphase I; in addition, a substantial number of univalents are found at this stage. In this paper we examine the later meiotic and post meiotic consequences of these irregularities in four leek cultivars and discuss their implications. Irregularities of chromosome segregation are observed at anaphase of both meiotic divisions, giving rise to micronuclei in dyad and tetrad stage pollen mother cells. It is shown that micronucleus frequency in tetrads is correlated with univalent frequency at metaphase I, suggesting that micronuclei originate largely from missegregation of univalents. Seedling populations of the same four cultivars were screened cytologically and shown to contain aneuploids at frequencies ranging between 4.3% and 8.4%. It is proposed that the majority of aneuploid seedlings originate from meiotic irregularity, especially univalent missegregation. It is very likely that the presence of this level of aneuploidy in the seedling populations contributes to the problems of phenotypic non-uniformity experienced by the leek crop, although its relative importance is difficult to assess. Further studies are required to establish the genetical and environmental contributions to meiotic irregularity and to assess the potential for selection for greater meiotic regularity in this material. This revised version was published online in July 2006 with corrections to the Cover Date.     

Plant regeneration via organogenesis and somatic embryogenesis in callus cultures derived from mature zygotic embryos of leek (Allium ampeloprasum L.)

Summary A high frequency plant regeneration system via organogenesis and somatic embryogenesis was established with callus cultures derived from mature zygotic embryos of different leek genotypes (Allium ampeloprasum L.). Four different callus types with varying morphogenetic potential were obtained. Relatively high concentrations of the auxin 2,4-dichlorophenoxy-acetic acid reduced callus weight and subsequent shoot regeneration and primordia formation of the callus. Shoot regeneration and primordia formation of the callus decreased after prolonged subculture on media containing 2,4-dichlorophenoxy acetic acid. A callus growth period of six weeks on Murashige and Skoog medium with 0.25–0.5 mg l^-1 2,4-dichlorophenoxy acetic acid showed the highest rate of shoot regeneration after transfer of callus to regeneration medium with 1 mg l^-1 kinetin.Differences between leek genotypes in callus type, callus weight, shoot regeneration and primordia formation were observed. Histological observations showed that plant regeneration took place, both via the pathway of somatic embryogenesis and organogenesis.Abbreviation 2,4-D 2,4-dichlorophenoxy acetic acid - MS Murashige and Skoog (1962) medium     

Genetic Analysis of Isozyme Loci in Chives (Allium schoenoprasum L.)

The inheritance ot nine isozyme systems in selfed progenies of chives was studied elcctrophoretically. The isozyme systems studied were malate-dehydrogenase (MDH), phosphoglucoisomerase (PGI), triosephosphate-isomerase (TP1), diaphorase (D1A), menadione-reductase (MDR), esterase (EST), glutamate-oxalacetate-transaminase (GOT), hexokinase (HK) and superoxide-dismutase (SOD). Segregation results of Goodness-of-Fit tests against the expected 1:2:1 and 3 : 1 ratios for codominant and dominant inheritance, respectively, led to the identification of 16 isozyme loci whose banding patterns are given in this paper. The first results on linkage relationships between isozyme loci and between the Mdr-3-locus and a male sterility gene are given. These results and further studies will be used to mark important characters in chives.     

Direct plant regeneration from leaf explants in cucumber (Cucumis sativus L.) is free of stable genetic variation

A new procedure is described for rapid and efficient plant regeneration from leaf explants of Cucumis sativus and C. anguria. The following factors were most important: young leaves, the NO₃: NH₄ ratio in the plant induction medium, small explants and the growth regulator combination. After about 4 weeks of culture under optimal growth conditions, the frequency of regeneration was 10–100% of explants. Six to 7 weeks were required to obtain well-rooted plants, which were mostly able to survive after transfer into soil. From a single young leaf of C. sativus cv. ‘Borszezagowski’, 135 plants could be regenerated. All plants transferred to a greenhouse were free of morphological or physiological abnormalities, flowered normally and bore fruits. The analysis of R₀ plants showed no genetic variation, whereas in the R₁ two new phenotypes, which were not transmittable to the R₂, were observed. This procedure is recommended for its production of homogeneous cucumber plants.     

Causal relationships between inbreeding, seed characteristics and plant performance in leek (Allium porrum L.)

Leek (Allium porrum L.) is an important outdoor vegetable in West Europe, where it is cultivated on about 30,000 ha. Most commercial cultivars of leek are open pollinated. One of the major problems with the crop is poor uniformity. Leek is an outbreeding species with up to 20% self-fertilisation. Much of the variation of open pollinated cultivars is explained by the strong sensitivity to in breeding depression after selfing. In this study we attempt to analyse in a systematic way the relationship between degree of selfing and agricultural performance in leek. The results obtained confirm a negative correlation between selfing and somea gricultural aspects important for vigour such as seedling emergence, plant growth and plant fresh yield. Also negative correlations between degree of selfing and seed individual weight and between selfing and seed individual size were found. The negative relationship between inbreeding and plant weight at harvest is further confirmed in an experiment in which the origin (cross-pollination orself-pollination) of each individual offspring plant analysed was determined using AFLP-markers. Finally, the correlation between chlorophyll deficiency genes and the loss of vigour that follows selfing was investigated. The results obtained demonstrate a significant decrease of pigment content in two generations of selfing. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic Control of Temperature-Sensitivity of Cytoplasmic Male Sterility (cms) in Chives (Allium schoenoprasum L.)

In earlier experiments with chives (Allium schoenoprasum L.) temperature-sensitive and temperature-insensitive cms plants could be selected. To obtain information about the site and nature of the genetic factor(s) responsible for the temperature sensitivity of the cms, temperature-insensitive and temperauire-sensitive cms plants were crossed with maintainers as well as with one another. In the progenies each genotype was cloned into two clone members, and these were examined concerning their male sterility under normal (20 °C/14 °C, day/night) as well as under constantly high temperatures (24 °C/ 24 °C). The results indicate that the temperature-sensitivity of the cms is controlled by a dominant nuclear gene “T”. This acts like a restorer gene at high temperatures and is ineffective at normal temperatures. Accordingly, important conclusions can be drawn with regard to the selection of temperature-insensitive cms-lines as well as to the propagation of the cmi-lines. The results are discussed in connection with the mitochondrial polypeptides probably responsible for the formation of the cms.     

Variation of gynogenesis ability in onion (Allium cepa L.)

Onion varieties from Northern-Europe, Eastern-Europe, Southern-Europe and the U.S. including populations, inbreds, synthetics and clones were tested for their gynogenesis ability for three years: 1993-1995. Embryos were induced in Petri dishes using in vitro culture of flower buds. Embryo rate, regeneration rate, survival rate, embryo quality and ploidy level of regenerants are described. Important genotype and variety effects are pointed out; embryo production and plant regeneration ranged from 0 to 17% and from 0 to 11% of inoculated flowers, respectively. Highest results were obtained with inbreds and synthetics for embryo production as well as for plant regeneration. Populations expressed various responses which were generally low. Geographic origin and year effects were covered by the effects of genetic structure of varieties and specific genotype of donor plant. Among regenerants, 80% were haploid and 13% were spontaneous diploid. No relation has been found between general quality and ploidy level of regenerants. The choice of plant material for successful gynogenesis in onion is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic Control of Tetracycline Sensitivity of Cytoplasmic Male Sterility (cms) in Chives (Allium schoenoprasum L.)

The expression of cms in chives is controlled by a cytoplasmic factor (5), a restorer gene X/x (Tatlioglu 1982) and a temperature gene T/t (Tatlioglu 1987). In recent investigations (Tatlioglu 1986) it could be shown that tetracycline also influences the expression of 0731. To obtain information about the genetic control of tetracycline sensitivity of cms, tetracycline-sensitive and tetracycline-insensitive cms plants were crossed with each other as well as with maintainers and the reaction of their progeny to tetracycline base was investigated. The results indicated that the promotion of fertility due to high-temperature conditions (24°C/24 °C, day/night) and tetracycline · base are independent of each other. The results of crosses can be explained by a nuclear gene, A/a, causing the tetracycline sensitivity when recessive. By using different genotypes of the three loci for restoration, temperature and tetracycline sensitivity highly advantageous material can be constructed for the investigation of the interaction between the nuclear and the mitochondrial genome in higher plants, for the molecular and functional basis of cms and for its use in plant breeding.     

The Genetic Basis of Variation for Salt Tolerance in Sorghum bicolor (L.) Moench Seedlings

The genetic basis of salt (NaCll tolerance at the seedling stage was examined in eight accessions of Sorghum bicolor (L.) Moench which differed in relative NaCl tolerance. The eight accessions were crossed in all possible combinations. The Nad tolerances of the resulting 56 F: hybrids and their eight parents were assessed after two weeks growth in solution cultures containing 0, 103, and 150mM NaCl. Indices of salt tolerance (relative tolerance) were used for analysis using the diallel method. Both additive and dominance effects appeared to be important for the expression of variation under low and high salinity levels, but the effect of genes with dominance properties was more pronounced. Estimates of narrow sense hentabilities for sail tolerance were appreciable, suggesting that rapid improvement in salinity tolerance is possible in this species using high selection pressures in the F₂ population.     

Genetic evaluation of cultivated garlic germplasm (Allium sativum L. and A. ampeloprasum L.)

Garlic cultivated in rural farms of South Italy is often a heterogeneous clone population, which can comprise different cytotypes. A collection of cultivated garlic from the University of Basilicata gene-bank, was evaluated for ploidy level, and 16 different morphological traits. Out of50 accessions, 7 were hexaploids (Allium ampeloprasum L.) and43 diploids (Allium sativum L.). Significant differences in yield were observed within and between ploidy levels. The heritable traits most correlated with yield were plant height (h² = 0.62) within diploid types and neck diameter (h² = 0.75) within hexaploids. Discriminant analysis did show that four characters (leaf basal width, total n^° of leaves, clove diameter and neck height) were able to correctly discriminate all germ plasm accessions between the two species. This revised version was published online in August 2006 with corrections to the Cover Date.     

Breeding potential of Belgian landraces of leek ( Allium ampeloprasum L. var. porrum)

Western Europe is the world's greatest leek producing and consuming region. Belgium is situated in the centre of Western Europe and can be considered as a genepool of landraces of leek. Although the commercial varieties nowadays take over the successes of Belgian landraces, this paper deals with the breeding potential of the Belgian landraces. Typing the Belgian landraces was done in an observation trial together with 50 cultivars. Clustering analysis revealed that 4 of the Belgian landraces were autumn types, 2 landraces were of the early winter type and another 12 landraces were ranged with 6 commercial varieties to form the most winterhardy group of leek. For the important characteristics leaf colour and senescence resistance, the Belgian landraces were better than most of the commercial varieties. Although, for economically more important characteristics shaft length and some disease resistance they scored low. Finally, in this trial, the Belgian landraces were high yielding, especially in the late season. But also in the early season (harvest in September and November) some Belgian landraces were in the top 10 for yield. At harvest in February 9 of the 10 best yielding winterleeks were Belgian landraces. This proves that the Belgian landraces were well adapted to the soil and climate of this region. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic variation of yellow-seeded rapeseed lines (Brassica napus L.) from different genetic sources

In order to breed yellow-seeded rapeseed, 16 yellow-seeded lines of Brassica napus L. derived from eight genetic sources were used. The genetic variation of the seedcoat ratio, the cellulose content of the seedcoat, the oil content of the seedcoat and of the embryo, and also the correlations between these characters of the yellow- and brown-seeded plants from the same line, were analysed by variance analysis and path analysis. The results show that the seedcoat ratio and cellulose content of brown seeds are 4.2% and 17.74%, respectively, higher than that of yellow seeds and the oil content of the seedcoat of brown seeds is 3% lower than that of the yellow seeds, these differences all being highly significant. However, the differences between yellow and brown seeds in 1000-seed weight and oil content of the embryo were very small. Both characters are determined mainly by the genetic background and not by seed colour or seedcoat thickness. The correlation analysis revealed that the seedcoat thickness has a highly significant positive correlation with the cellulose content of the seedcoat and is highly significantly negatively correlated with the seedcoat oil content and the 1000-seed weight. The oil content of the embryo alone has a highly significant negative correlation with 1000-seed weight. In yellow seeds, the seedcoat thickness has a large and directly positive effect on the oil content of the embryo whereas the 1000-seed weight has a negative one; the opposite was found in brown seeds. Selection objectives in breeding yellow seeds in Brassica napus are also discussed.     

Plant regeneration in sweet potato (Ipomoea batatas L., Convolvulaceae)

The application of new techniques for improvement of sweet potato crops, particularly including the exploitation of somaclonal variation, gene transfer by genetic transformation and somatic hybridization, requires the control of plant regeneration from tissue cultures. Shoots can easily be regenerated from explants of stems, petioles, leaves and roots, while callus cultures do not produce any shoots. The potential of somatic embryogenesis and plant regeneration via embryogenesis was evaluated for 10 cultivars of sweet potato. Protocols for plant regeneration from cultured protoplasts have also been developed. Since mesophyll was resistant to enzyme digestion, fragments of stems and petioles, callus and cell suspensions were used as source of protoplasts of sweet potato. Series of transfers of protoplast-derived calluses, particularly those which had been obtained from in vitro plants, to media containing a high level of zeatin resulted in successful formation of shoots in only two sweet potato cultivars. In addition, the embryogenic potential was irreversibly lost through protoplast culture, since protoplasts isolated from embryogenic cell suspensions developed into non-embryogenic callus. Consequently, an alternative protocol is being successfully developed to improve plant regeneration from cultured protoplasts of sweet potato, involving first root formation from which shoots can then be regenerated. Preliminary evaluation in field conditions in Gabon revealed that plants regenerated from cultured protoplasts exhibited a great genetic variability in their growth and tuber formation in particular. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic control of frost tolerance in wheat (Triticum aestivum L.)

Summary The frost tolerance of winter wheat is one component of winter hardiness. If seedlings are frost resistant, it means that they can survive the frost effect without any considerable damage. To study the genetic control of frost tolerance, an artificial freezing test was used. Frost tolerance is controlled by an additive-dominance system. The results of diallel analyses indicate the importance of both additive and non-additive gene action in the inheritance of this character. The dominant genes act in the direction of lower frost tolerance and the recessive genes in the direction of a higher level of frost tolerance. The results of monosomic and substitution analyses show that at least 10 of the 21 pairs of chromosomes are involved in the control of frost tolerance and winter hardiness. Chromosomes 5A and 5D have been implicated most frequently. The geneFr1 (Frost 1) was located on the long arm of chromosome 5A. Crosses between cultivars, chromosome manipulation and the induction of somaclonal variation may be suitable methods for broadening the gene pool for frost tolerance.     

洋葱种质资源遗传多样性的ISSR分析

应用ISSR标记对32份洋葱种质资源的遗传多样性进行了分析。从31个ISSR引物中筛选出4条扩增产物条带清晰、多态性高的引物,在32份资源样品中共扩增出39条带,其中31条带为多态性位点,平均每个引物扩增的多态带数为7.75条,多态性条带比率（PPB）为79.48%。资源间的遗传相似系数在0.552~0.960之间,具有较为丰富的遗传多样性。ISSR聚类分析表明,在L取值为D=0.68时,可将32份洋葱资源分成5类：第一类包括18份种质资源,主要以Yellow Sweet Spanish系统为主;第二类包括1份种质资源,为Bejo Daytona;第三类包括3份种质资源,为Yellow Globe系统;第四类包括9份种质资源,为Yellow globe danvers系统;第五类包括1份种质资源,为Yellow Danvers system系统。较好地揭示了洋葱种质资源间的遗传多样性与亲缘关系,可为洋葱遗传育种和杂交亲本选择提供科学依据。     

Genetic variation in the olive tree (Olea europaea L.) cultivated in Morocco

Summary Genetic variation was studied using enzyme polymorphism at 8 loci in ancient olive trees. These were being cultivated in 10 sites along a transect from North (Pre-Rif) to South (Anti-Atlas), involving the main ecological areas where the species is cultivated in Morocco. For the 328 trees studied, 16 alleles and 68 multilocus genotypes, of which one was present in more than half the individuals analysed, were detected. Eighty seven per cent of the total genetic diversity was attributable to within site variation and showed a high proportion of local genotypes. The highest values for both genotype number and heterozygosity were observed in the South of Morocco. Such high variation may be due to the partial domestication of olive material which may be derived from crosses between cultivars or between cultivars and feral or wild olive (oleaster) trees growing frequently in the Southern region. Genetic diversity in Moroccan olive, constitutes an important genetic resource which must be conserved for further breeding.     

Genetic variation of sweet potatoes (Ipomoea batatas L.) cultivated in Chile determined by RAPDs

RAPD (randomly amplified polymorphic DNA) technology was applied to analyze the genetic variability of sweet potato germplasm existing in Chile and elsewhere. Analysis of 28 cultivars from all over the world showed polymorphic bands with all 18 primers tested. A total of 124 RAPD bands were scored with an average of 6.9 polymorphic bands per primer. These results confirm that sweet potato exhibits high genetic variation. Two groups were distinguished: one containing Peruvian cultivars, and another containing cultivars from the rest of the world. Analysis of 14 accessions from Central Chile and one from Northern Chile showed polymorphic bands with 24 of 26 primers tested, but almost all of the 140 polymorphic bands merely showed the distinctness of the Northern accession. The almost complete uniformity of the other 14 accessions shows that sweet potato germplasm collected in Central Chile has very little genetic variability and may be derived from a single cultivar. Based on these results and on historical records, some hypotheses are proposed to explain the origin of sweet potatoes cultivated in Chile. This revised version was published online in July 2006 with corrections to the Cover Date.     

Selection of a highly-regenerative genotype of white clover (Trifolium repens L.) and plant regeneration from protoplasts derived from this genotype

Summary Callus cultures were induced from hypocotyl sections of 24 varieties of white clover (Trifolium repens L.). The calli did not show any significant difference of growth among the varieties. After the calli has been transferred to three regeneration media, green-spot formation was observed on calli derived from some seedlings. Remarkable intra- and intervarietal variations in the emergence of green spots and some trends between the origin of varieties and the frequency of green spots were observed. In most cases, the green spots turned brown without showing further differentiation, and only two genotypes formed shoots. A callus from a seedling of the Swedish variety Undrom has sustained high levels of plant regeneration throughout 24 months of culture. Protoplasts derived from this selected genotype were divided into cell colonies. 8P (Kao, 1977) medium containing 0.5 mg/1 2,4-D and 0.5 mg/1 kinetin was the most suitable medium for inducing divisions in protoplasts. When subcultured into solid B5 medium, the colonies produced calli, which when transferred to a regeneration medium, formed shoots. This genotype is expected to a useful subject for genetic engineering of white clover.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - IAA indole-3-acetic acid - 2ip 6-, -dimethylallylamino purine - NAA -naphthaleneacetic acid     

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.     

Genetic variation and changes with ontogeny of osmotic adjustment in sunflower (Helianthus annuus L.)

Summary Intraspecific variation for osmotic adjustment in sunflower was examined using a collection of 33 genotypes of different origin which were exposed to water stress at the 8-leaf stage. Changes in osmotic adjustment with ontogeny were also evaluated in the pre- and post-anthesis phases using seven genotypes drawn from this collection. Estimates of osmotic adjustment were derived from measurements of leaf relative water content (RWC) and osmotic potential () during a period in which the soil was allowed to dry out gradually. The degree of osmotic adjustment, expressed as the value of RWC for a of –1.7 MPa (RWCe), was derived from the ln RWC/ln relationship. Both monophasic and biphasic ln RWC/ln relationships were found. Irrespective of the form of the relationship, all genotypes at the 8-leaf stage showed some degree of osmotic adjustment. This was also true for the cultivars included in the subset examined in pre- and post-anthesis phases. Significant differences (P=0.05) in RWCe were found between extreme genotypes in all three phases.Significant (P=0.05) linear relationships were found between RWCe measured in the 8-leaf stage and that measured in the pre- and post-anthesis phases, establishing the viability of measurements in the 8-leaf stage as a means of selection for osmotic adjustment in later developmental stages. Genotype rank order was stable (P=0.01) across the three ontogenetic phases examined.Abbreviations ETp potential evapotranspiration - osmotic potential - RWC relative water content - RWCe value of RWC for a of –1.7 MPa