Generation Of Interspecific Hybrids Research Articles

Effect of different cytokinin sources on in vitro/ex vitro multiplication and rooting rate in Eucalyptus spp.

Eucalyptus globulus Labill. is of great interest to the pulp industry. However, the species is highly susceptible to leaf spot caused by Teratosphaeria nubilosa and has a low rooting capacity. In order to overcome these limitations, INIA has been implementing a genetic improvement program for this species and the generation of interspecific hybrids. The strategy is based on the selection of E. globulus clones with high precocity or foliage turnover, since the adult foliage is more tolerant to T. nubilosa. In addition, controlled crosses of E. globulus and E. maidenii with E. grandis are carried out to incorporate disease resistance and ease of rooting. The multiplication of the selected materials is carried out by micropropagation, but the low rooting capacity is a trait that needs improvement. The cytokines necessary for in vitro proliferation can have a negative effect on the rooting process. Benzyladenine is the most commonly used cytokine because of its low cost and easy availability, with some negative effects on rooting, while meta-topolin is a cytokine of lesser impact. The objective of this study was to evaluate the effect of benzyladenine and meta-topolin on the multiplication rate, rooting percentage and plantlets survival of E. globulus, E. grandis × E. globulus, and E. grandis × E. maidenii. In multiplication media, benzyladenine was supplied at 0.4 µM, while two concentrations of meta-topolin (0.4 and 2 µM) were used. Preliminary results indicated a higher multiplication rate with the inclusion of meta-topolin in both concentrations. The in vitro rooting percentage of explants treated with meta-topolin was 51% and 44%, at 0.4 and 2 µM, respectively, while with benzyladenine was lesser (37%). After 28 days post-transplanting, survival was higher in meta-topolin-derived plants. Meta-topolin improved multiplication, in vitro rooting and acclimation of plants. The use of this hormone could improve micropropagation protocols, facilitating rooting and multiplication of valuable genotypes.

Heterosis versus breakdown in cyprinid hybrids associated with SVCV infection revealed by transcriptome profile analysis of head kidney

Whilst the hybrids of F1 generations usually experience heterosis for fitness-related traits (including the resistance to parasites), post-F1 generations, due to Dobzhansky–Muller genetic incompatibilities, express numerous disadvantageous traits (including susceptibility to parasites). Genetic disruption in hybrids may also result from the broken system of cyto-nuclear coadaptation. Maternal backcrosses (having parents with the same mtDNA) and paternal backcrosses (having parents with different mtDNA) have the same nuclear genetic compositions, but differ in cytoplasmic genetic elements, affecting their viability and survival.Spring viraemia of the carp virus (SVCV), a disease with a serious economic impact in aquacultures, affects almost exclusively cyprinids, primarily common carp (Cyprinus carpio), and causes high mortality, whilst gibel carp (Carassius gibelio) is a less susceptible species. Our study was focused on the transcriptome profile analysis of head kidney to reveal differential gene expression in highly susceptible common carp, weakly susceptible gibel carp, and hybrid lines, hypothetizing that the patterns of differential gene expression will reflect hybrid heterosis in F1 generations and hybrid breakdown in backcrosses and F2 generations. We expected the differences in differential gene expression between maternal and paternal backcrosses to be in line with the hypothesis of broken cyto-nuclear coadaptation.The pattern of differential gene expression revealed from the transcriptomic analysis of head kidney was linked to the resistance or susceptibility to SVCV infections in two pure species, C. gibelio and C. carpio, and their various generations of inter-specific hybrids. We evidenced hybrid heterosis for F1 generations of hybrids, mostly reflected by similarity in the down-regulation of differentially expressed genes classified within the viral infection disease category. High hybrid breakdown was documented throughout the transcriptomic analysis for paternal backcross generations and F2 generation of hybrids, confirming the broken system of cyto-nuclear coadaptation in those post-F1 generations. This evidence may support the role of intrinsic selection acting against inter-specific hybridization in freshwater fish.

The apricot as a source of self-compatibility and Plum pox virus resistance in the generation of interspecific hybrids Prunus salicina Lindl. × Prunus armeniaca L. (plumcots)

The apricot as a source of self-compatibility and <i>Plum pox virus</i> resistance in the generation of interspecific hybrids <i>Prunus salicina</i> Lindl. × <i>Prunus armeniaca</i> L. (plumcots)

Morphology is a poor predictor of interspecific admixture – the case of two naturally hybridizing newts Lissotriton montandoni and Lissotriton vulgaris (Caudata: Salamandridae)

Abstract Compared to the parental species, interspecific hybrids often show intermediate phenotypes which can affect their fitness directly and/or their attractiveness to potential mates. Lissotriton montandoni and Lissotriton vulgaris hybridize across their parapatric range along the Carpathian mountains. Hybrids are rare in natural hybrid zones, which may be related to strong assortative mating in parental species. In the present study, we investigated morphological male species-specific traits and their differentiation between both parental species and first generation of interspecific hybrids (F1), considering morphological variation between two L. vulgaris subspecies co-occurring with L. montandoni in nature: L. v. vulgaris and L. v. ampelensis. Male morphology of each group was assessed and compared based on species-specific and sexual secondary traits, selected based on the literature review. We confirmed that F1 hybrids of L. v. vulgaris and L. montandoni have an intermediate morphology between parental species. However, when morphological traits were compared with the level of genetic admixture of individuals in natural hybrid zones, we discovered that even early generations hybrids (i.e. F1 and/or F2 generation) can be similar to the parental species (especially L. v. ampelensis). As even early generations hybrids can be morphologically undistinguishable from L. v. ampelensis, sexual attractiveness of hybrids may be potentially less affected in direction of L. v. ampelensis backcrossing. Summarizing, morphology, especially morphology of male secondary sexual traits is not a reliable tool for the estimation of genetic admixture of an individual in natural populations within the hybrid zone.

USE OF INTERSPECIFIC HYBRIDIZATION IN THE BREEDING OF ADAPTIVE HYBRIDS AND SORTS OF GARDEN CHRYSANTHEMUM (Chrysanthemum morifolium Ramat.)

Many garden chrysanthemums bred across the world are not fully winter hardy. Many are damaged by fungal diseases due to a high humidity and are late flowering. This makes them unsuitable for general commercial marketing. Since 2000 we have been conducting a breeding program using natural species of the genus Chrysanthemum that are adapted to the local conditions. The strategy of breeding adaptive hybrids and varieties of chrysanthemum native to Russia was proposed based on their biological, genetic peculiarities and natural resources of Chrysanthemum with the use of interspecific hybridization. Research objects are the first generations of interspecific hyb rids of F1obtained previously by the author as a result of the hybridization of varieties and wild species of Chrysanthemum. Derived from different species and varieties, F1hybrids were crossed among themselves to obtain the multicomponent F2progeny. F2seedlings with winter hardiness, resistance to Puccinia horiana Henn. and early flowering were used in closely related crosses. The offspring of F3from closely related crosses were also assessed and selected according to adaptive and decorative characteristics. Inclusion in the selection process of various sources of winter hardiness and resistance to P. horiana allowed positive characteristics to be increased in F2and to be revealed in F3. Adaptive signs of the wild species Chrysanthemum naktongense Nakai, C. coreanum (H. Lév. et Vaniot) Nakai, C. zawadzkii var. tenuisectum Kitag., C. leiophyllum Nakai, and C. zawadzkii subsp. acutilobum (DC.) Kitag., which have formed and fixed during evolution, were inherited and manifested in offspring of the multicomponent hybrids and the closely related crosses. Promising interspecific forms with biological signs determining the possibility of growing in extreme conditions of the subregion were selected.

Production of androgenetic, triploid and tetraploid hybrids from the interspecific hybridization of female Japanese crucian carp and male blunt snout bream

Distant hybridization occurs widely in fishes and is a useful strategy to produce different ploidy offsprings. In this study, we obtained androgenetic blunt snout bream (2n = 48, ADBSB), triploid hybrids (3n = 124, 3nJB) and tetraploid hybrids (4n = 148, 4nJB) from the hybridization of two species from different subfamilies: Carassius cuvieri (♀, 2n = 100, JCC) and Megalobrama amblycephala (♂, 2n = 48, BSB). The ploidy levels of ADBSB, 3nJB and 4nJB hybrids were confirmed by counting chromosomal numbers, forming chromosomal karyotype, and measuring DNA content. In the phenotypes and reproductive traits, 3nJB and 4nJB exhibited significantly divergences from JCC and BSB, but ADBSB took after BSB. Fluorescence in situ hybridization (FISH) and 5S rDNA analyses revealed that the genetic traits of the offsprings compared with those of their parents. This is the first report on the coexistence in vertebrates of viable androgenetic, triploid and tetraploid hybrids being produced by crossing JCC and BSB. The formation of the different ploidy offspring is great significance in both evolution and fish genetic breeding and it also provides a good model for studying the genomic variation in the first generation of interspecific hybrids.

Generation of interspecific hybrids between Trifolium vesiculosum and T. alexandrinum using embryo rescue

Interspecific hybrids were developed between Trifolium alexandrinum cultivar Wardan × Trifolium vesiculosum and T. alexandrinum cultivar BL1 × T. vesiculosum through embryo rescue, as the crosses failed to set seed under natural conditions. Trifolium vesiculosum was used as a donor/male parent in this study as it is reported to possess tolerance to stem rot and high forage yield. Fertilization in crossed florets of the crosses was manifested from the recovery of swollen ovaries ( 93.00%) of the swollen ovaries. The hybrid embryos at various developmental stages (heart, torpedo and cotyledonary) were rescued at a frequency of 2.56% from Wardan × T. vesiculosum and 6.12% from BL1 × T. vesiculosum. Differentiation occurred only in the cotyledonary stage embryos, resulting in 17 putative interspecific hybrid plantlets. The assessment of plantlet hybridity through SSR markers (for the alleles inherited from the donor parent), micromorphological leaf traits (leaf texture and stomata) and morphological characters (plant height, leaflet length and width) confirmed production of two interspecific hybrids designated as AV1 and BV3 representing both the crosses. AV1 displayed moderate resistance and BV3 was resistant to stem rot.

Chinese cabbage (Brassicarapa ssp. pekinensis) \u2013 a valuable source of resistance to clubroot (Plasmodiophora brassicae)

Clubroot, caused by the protozoan parasite Plasmodiophora brassicae Woronin, is one of the most damaging diseases of Brassica napus worldwide. Resistant plant material is valuable for cultivation in all areas of high incidence of the disease and intensive growth of oilseed rape. We have evaluated clubroot resistance, plant morphology and seed quality in 15 lines of an F4 generation and selected six lines of F5 generation of interspecific hybrids obtained from a cross between a male sterile line of B. napus ‘MS8’, selected from resynthesized oilseed rape (B. rapa ssp. chinensis × B. oleracea var. gemmifera) and an ecotype of B. rapa ssp. pekinensis. Clubroot resistance was evaluated using a bioassay with P1-P5 pathotypes of P. brassicae (according to the classification of Somé et al. 1996). The resistance to the pathotype P1 was successfully fixed in the F5 generation, and improved in some lines in respect to the pathotypes P2-P4. The resistance to P1 and the other tested pathotypes was not linked. Characterization of plant material included recent techniques of FISH and BAC-FISH with a special focus on the analysis of ribosomal DNA (rDNA) of selected individuals. Two hybrid lines combined high levels of resistance with appropriate plant morphology, good seed quality traits and a stable chromosome number and arrangement. Recent techniques of ‘chromosome painting’ provided good insight into chromosome organization in the hybrids obtained, and offered opportunities of further improvement of the breeding process.

Organization and Variation Analysis of 5S rDNA in Different Ploidy-level Hybrids of Red Crucian Carp × Topmouth Culter

Through distant crossing, diploid, triploid and tetraploid hybrids of red crucian carp (Carassius auratus red var., RCC♀, Cyprininae, 2n = 100) × topmouth culter (Erythroculter ilishaeformis Bleeker, TC♂, Cultrinae, 2n = 48) were successfully produced. Diploid hybrids possessed 74 chromosomes with one set from RCC and one set from TC; triploid hybrids harbored 124 chromosomes with two sets from RCC and one set from TC; tetraploid hybrids had 148 chromosomes with two sets from RCC and two sets from TC. The 5S rDNA of the three different ploidy-level hybrids and their parents were sequenced and analyzed. There were three monomeric 5S rDNA classes (designated class I: 203 bp; class II: 340 bp; and class III: 477 bp) in RCC and two monomeric 5S rDNA classes (designated class IV: 188 bp, and class V: 286 bp) in TC. In the hybrid offspring, diploid hybrids inherited three 5S rDNA classes from their female parent (RCC) and only class IV from their male parent (TC). Triploid hybrids inherited class II and class III from their female parent (RCC) and class IV from their male parent (TC). Tetraploid hybrids gained class II and class III from their female parent (RCC), and generated a new 5S rDNA sequence (designated class I–N). The specific paternal 5S rDNA sequence of class V was not found in the hybrid offspring. Sequence analysis of 5S rDNA revealed the influence of hybridization and polyploidization on the organization and variation of 5S rDNA in fish. This is the first report on the coexistence in vertebrates of viable diploid, triploid and tetraploid hybrids produced by crossing parents with different chromosome numbers, and these new hybrids are novel specimens for studying the genomic variation in the first generation of interspecific hybrids, which has significance for evolution and fish genetics.

Elimination of the parental its1 region of rDNA in the first generation of interspecific hybrids between the bream Abramis brama (L.) and roach Rutilus rutilus (L)

Elimination of the parental its1 region of rDNA in the first generation of interspecific hybrids between the bream Abramis brama (L.) and roach Rutilus rutilus (L)

Engineering evolution to study speciation in yeasts.

The Saccharomyces 'sensu stricto' yeasts are a group of species that will mate with one another, but interspecific pairings produce sterile hybrids. A retrospective analysis of their genomes revealed that translocations between the chromosomes of these species do not correlate with the group's sequence-based phylogeny (that is, translocations do not drive the process of speciation). However, that analysis was unable to infer what contribution such rearrangements make to reproductive isolation between these organisms. Here, we report experiments that take an interventionist, rather than a retrospective approach to studying speciation, by reconfiguring the Saccharomyces cerevisiae genome so that it is collinear with that of Saccharomyces mikatae. We demonstrate that this imposed genomic collinearity allows the generation of interspecific hybrids that produce a large proportion of spores that are viable, but extensively aneuploid. We obtained similar results in crosses between wild-type S. cerevisiae and the naturally collinear species Saccharomyces paradoxus, but not with non-collinear crosses. This controlled comparison of the effect of chromosomal translocation on species barriers suggests a mechanism for the generation of redundancy in the S. cerevisiae genome.

High regeneration potential in vitro of sunflower (Helianthus annuus L.) lines derived from interspecific hybridization.

Successful selection of interspecific hybrid progenies with superior ability to regenerate shoots from apical meristems was performed in sunflower which now allows for the development of lines for improved biotechnological applications. Early generations of interspecific hybrids originating from crosses between the two H. annuus CMS lines ‘HA89’ and ‘Baso’, and 9 wild species were screened for their ability to regenerate in vitro. Evaluation of 36 progenies allowed to identify seven progenies from crosses involving H. mollis, H. giganteus, H. strumosus, and H. decapetalus which showed a significantly higher regeneration potential than the commercial hybrid ‘Albena’ regarding the number of shoots per explant. Among these progenies, 47.2 to 62.4% of explants produced shoots with an average of 2.3 to 3.5 shoots per cultured explant. Regeneration in vitro was significantly determined by the genotype. More than half of the investigated interspecific hybrids performed better than the inbred ‘HA89’ demonstrating that the high regeneration potential available in the wild species can be efficiently transferred to cultivated sunflower. The seven progenies with high regeneration potential in vitro were characterised by agronomic performance in the field. Two of the interspecific hybrids derived from H. strumosus and H. decapetalus not only showed a superior regeneration potential but also proved to be competitive to commercial hybrids with regard to important agronomic traits, e.g. fat content and TGW.

Hybrid Sterility: Eupyrene Sperm Production and Abnormalities in the Backcross Generations of Interspecific Hybrids between Heliothis subflexa and H. virescens (Lepidoptera: Noctuidae)

Sterile males from the backcross generations (BC) 40–49 and 72–79 of Heliothis subflexa (Guenee) females × Heliothis virescens (F.) males (fertile females crossed to H. virescens males each generation) were studied to determine the basis of sterility. BC males produce normal numbers of eupyrene sperm bundles in the testis, but in 50 to 90% of the BC males no eupyrene bundles descend from the testis to the duplex region of the reproductive tract. BC males that do have eupyrene sperm bundles in the duplex have significantly fewer than fertile H. virescens males. Electron microscope studies of the BC duplex bundles showed frequent rupture of the bundle exposing the individual sperm tails with swollen areas or blebs located along the tail region. These swellings were characterized by enlargement and rupture of the extracellular sheath, enlarged mitochondrial derivatives, sloughing off of the membrane associated with the mitochondrial derivatives, and the appearance of tubular aggregates. Absence of eupyrene sperm bundles in the duplex or abnormalities in the sperm tails most likely account for the sterility of BC males.

Persistence of Abnormal Spermiogenesis in the Backcross Generations of Interspecific Hybrids between Heliothis virescens1 X H. subflexa1

Simplified cytological procedures were developed for high resolution light microscopical study of sperm bundle structure in Heliothis virescens (F.). It was possible to separate parental, F1 hybrids ( H. subflexa (Guenee) females X H. virescens males), and backcross individuals (F1 female backcrossed to H. virescens male) on the basis of characteristic spermiogenic abnormalities. The abnormalities include alterations in individual sperm cells, abnormality in sperm cell organization within a bundle, and gross degenerative changes in bundle structure. In H. virescens, 0–2.2% of the eupyrene sperm bundles were defective; in the F1, 75.9–100% were defective; and in BC individuals, 25.4–100% were defective. Thus, there was severe impairment of the normal process of spermiogenesis. Males from the 2 parental strains and the F1 hybrids always had eupyrene sperm bundles in the duplex; BC1,11,50 males often had none or significantly fewer sperm bundles. The method can differentiate H. virescens males from either F1 or BC males found in field collections during a suppression program involving hybrid sterility.

Variation in pollen and ovule fertility in varieties of cassava, and the effect of interspecific crossing on fertility

Records of the set of seeds obtained from intraspecific cassava crosses, from interspecific crosses between other Manihot species and cassava, and from backcrosses to cassava of three generations of interspecific hybrids are used to assess the variation in pollen and ovule fertility. It is concluded that the capacity of cassava varieties to set seeds has been reduced since they have evolved from non-tuberous wild forms and have been propagated vegetatively. Fertility was found to be very variable, and the capacity of the pollen of a variety to promote seed-set was not related to the fertility of the variety's female flowers. This situation would be expected if reduction in the fertilities of the two sexes were caused either by loss of balance in the genes controlling the functioning of the male gametophyte, or by unbalance of those concerned with the functioning of the female gametophyte or the tissues which nurture the embryo. Additional causes of sterility, probably including meiotic irregularities, appeared to operate in the F1 interspecific hybrids, but such factors were probably not important after the first backcross generation. Manihot melanobasis, a wild form which is normally propagated by seed and whose relationship to cassava should be regarded as subspecific, contributed factors which enhanced the fertility of its hybrids with cassava. This form could be used in cassava breeding as a “donor” of seed fertility, but use could also be made of some existing varieties which still possess a moderately high capacity to set seed. It is desirable to select these as one parent when making difficult crosses.