The evolutionary implications of interspecific hybridization among four species of zinnia sect. Mendezia (compositae)

Fertile interspecific hybrids were obtained among four species ofZinnia sect.Mendezia. The collection data and the segregation for ray color in F₁ hybrids suggest natural interspecific hybridization. Cytological data suggest that the descent of the four species from a common ancestor was accompanied by reciprocal translocations involving non-homologous chromosomes.     

The origin ofMentha X gracilis (Lamiaceae). I. Chromosome numbers,Fertility, and three morphological characters

Employing nine clones ofMentha arvensis and four clones ofM. spicata, 932 F, hybrids were synthesized and compared to 20 clones ofM. x gracilis. Two clones ofM. x gracilis with 60 somatic chromosomes were matched to a selected F₁ hybrid. The other 18 clones ofM. x gracilis had somatic chromosome numbers of 60, 72, 84, and 96, and while these chromosome numbers appeared in the F₁ progeny, morphological matches correlated with their correct chromosome numbers were not synthesized. The range of pollen and seed fertility, as well as the inheritance of male-sterility, leaf pubescence, and crispness, indicates that no one character can be used to identifyM. x gracilis, but all characters can be explained fromM. arvensis x M. spicata.     

Chromosome studies in species and hybrids ofPetrorhagia sect.Kohlrauschia (Caryophyllaceae)

Cytogenetic investigations have been made in the fourPetrorhagia species and hybrids of the sectionKohlrauschia. The three diploid species show close similarities in chromosome number, size and morphology, with the exception ofP. velutina, where one pair of metacentric chromosomes is represented by a pair of telocentrics. Meiotic studies in hybrids indicate close genomic homology between the diploid species and also between the two floral forms ofP. prolifera. The tetraploidP. nanteuilii behaves as an allotetraploid forming only bivalents at meiosis and results suggest thatP. velutina andP. prolifera are the diploid progenitors of this species. Since meiosis in diploid and triploid hybrids results in extensive intergenomic pairing it is concluded that the natural tetraploid has a bivalent promoting mechanism that prevents pairing between the genomes of its diploid progenitors.     

Introgressive hybridization in two southern California species of Rhus (Anacardiaceae)

Five populations ofRhus integrifolia andR. ovata were studied and, based upon morphological characteristics and pollen viability, a number of putative hybrids were found in those areas where the two species are sympatric. Diagnostic characteristics most useful for distinguishing the species and their hybrids are leaf morphology, sepal pubescence, petiole length, and petal size. Introgression was evident in at least three populations, which suggested that hybridization between the two species is an ancient phenomenon. Evolutionarily, hybridization between the two taxa has probably been of little consequence.     

Characterization of B chromosomes in Lilium hybrids through GISH and FISH

Supernumerary (B) chromosomes and small aberrant chromosomes were detected in Lilium hybrids and characterized through genomic in situ hybridization (GISH) and florescence in situ hybridization (FISH). Two small, supernumerary or B chromosomes were detected as extra chromosomes in a tetraploid plant derived from chromosome doubling of a hybrid (2n = 2x = 24) between a cultivar of the Longiflorum (L) and the Trumpet (T) group. When this tetraploid LLTT hybrid was crossed with a triploid LLO hybrid (O = Oriental), the B chromosome was transmitted to 73.4 % of the progenies. Based on GISH and FISH characterization, it was shown that the B chromosome consisted of two identical arms, with 5S rDNA hybridizing to the majority of it, which were flanked by normal telomeres, suggesting that this is an isochromosome. In another population, which is a backcross progeny between a F1 hybrid of Longiflorum × Asiatic (LA) and its Asiatic parent, the former produced functional 2n gametes which resulted in a triploid LAA progeny (2n = 3x = 36), in which three exceptional plants possessed 35 normal chromosomes and a small aberrant chromosome instead of the expected normal number of 36. In all three cases, the small aberrant chromosomes were isochromosomes which had obviously originated during the first backcross generation. These three chromosomes showed normal telomeres and mitosis. In addition, one of the new generated chromosomes possessed two 45S rDNA sites in the proximal positions. These new arisen isochromosomes were proposed to originate from centric breakage and fusion of two short arms of the missing chromosome in three genotypes, respectively, based on the comparison of arm lengths as well as rDNA loci. Their relevance to the origin of Bs is discussed.     

A systematic study of the genus hulsea (Asteraceae)

A systematic treatment based on genetic, biochemical, and morphological studies is presented for the 11 recognized taxa ofHulsea. A uniform diploid complement of 38 chromosomes was found in the 37 populations examined, including all species and representing first reports forH. brevifolia, H. californica, andH. mexicana. Thirteen flavonoid compounds, based on the aglycones quercetin, apigenin, cyanidin, and the 4′-O-methyl ether of luteolin, were detected inHulsea. Patterns of the flavonoid compounds are discussed with respect to the systematic treatment. The results of 595 synthetic crosses indicate thatHulsea species are self-incompatible, relatively cross-compatible, and that their F₁ hybrids are relatively fertile. Heterozygosity for one or two translocations is reported for 11 interspecific and intersubspecific hybrid combinations.     

An autosomal gene assignment in a marsupial: The gene for LDH-A is on chromosome 5 of the red kangaroo,Macropus rufus

A number of somatic cell hybrids between red kangaroo (Macropus rufus) and mouse cells, which lose marsupial chromosomes, were found to express the kangaroo form of LDH-A. Concordance between the expression of marsupial LDH-A and the presence of chromosome 5 in the hybrid cells and selected subclones enabled the gene for LDH-A to be assigned to this chromosome. This is the first autosomal gene assignment in a marsupial and should prove important for chromosome mapping in the red kangaroo and in many other species of marsupials.     

Cytotaxonomy ofCalliphoridae (Diptera)

A modification of the general system of classification ofCalliphoridae is proposed in this report. Information about the chromosome complements of about 90 species is provided including references to the earlier literature on chromosomes of this family. With one exception all species studied by us or by earlier investigators have 2n=12. The total complement length of 556 complements from 83 species averaged 66.4 μ. Most species have a short heteromorphic sex pair but the size and morphology vary considerably and one species,Hemipyrellia fernandica, seems to have a quadrivalent sex-chromosome complex in a 2n=14 complement. The autosomal pairs vary in both length and arm ratios between the species but seem to be more stable than the sex chromosomes. Only minor variations were found between different collections of the same species except for two collections ofCalliphora croceipalpis. Although presently available data on the chromosomes of Diptera species suggest that increases in total complement length accompany evolutionary progress, no such general trends were obvious in either the total complement lengths or chromosome morphology, either within or between the tribes ofCalliphoridae. Thus the karyotypical reorganizations in the family have apparently not been directly associated with changes in the general morphological features of the adults which may have responded in these respects more extensively to genetic mutations.     

Somatic hybridization between Nicotiana rustica and N. sylvestris

Protoplasts isolated from cell cultures of chlorophyll-deficient Nicotiana rustica cv. chlorotica and wild-type N. sylvestris were fused. The scheme for selection of somatic hybrids was based on the inability of the protoplast-derived colonies of the parental species to turn green; N. sylvestris protoplasts also had a very low plating efficiency in the medium employed. A total of 777 green colonies which were presumptive hybrids were isolated within four weeks of the fusion experiments. One hundred and eight green colonies formed shoots in vitro and 16 lines were rooted and grown in the greenhouse. Each of these hybrid plants displayed vegetative and floral traits intermediate to those of the parental species, except for plant height which in almost all cases was greater in the hybrids. Isozyme analyses by gel electrophoresis and isoelectric focussing of the small subunit of ribulose 1,5-bisphosphate carboxylase/oxygenase (RUBPCase) demonstrated that the nuclear genomes of both parents were expressed by the hybrids. Each of the eight somatic hybrid plants analyzed expressed only the N. rustica chloroplast genome as shown by isoelectric focussing of the large subunit of RUBPCase. This study demonstrated the value of N. rustica cv. chlorotica as a parental line in somatic hybridization with N. sylvestris and it might have widespread use with wild-type lines of other species.     

Reproductive relationships between annual species ofCalendula (Compositae)

Breeding experiments were carried out inCalendula species. In the annuals, which are selfers, rarely some outcrossing was observed only in the most peripheral flowers. In experimental crosses fruit was produced in all combinations. Fertile F₁ and F₂ hybrids could be grown from crosses between parents with similar chromosome numbers:C. palaestina ×C. pachysperma and crosses of different morphological forms ofC. arvensis. In crosses of species with different chromosome numbers at least partly fertile F₁ hybrids were obtained fromC. tripterocarpa ×C. stellata andC. tripterocarpa ×C. arvensis and crosses of the latter withC. palaestina. Fertile F₂ plants were grown from the combination ofC. arvensis ×C. tripterocarpa. Considering this information and previously obtained data, a scheme is proposed for explaining speciation in the genusCalendula.     

Forest and laboratory evaluations of hybridizedApanteles melanoscelus [Hym.: Braconidae], a parasitoid ofPorthetria dispar [Lep.: Lymantriidae]

Hybrids ofApanteles melanoscelus (Ratzeburg) were produced from colonies originating from France, Yugoslavia, and Connecticut. All strains, as well as freshly collected “wild” Connecticut parasitoids of the same species were evaluated in the laboratory for developmental rate, host attack rate, and sex ratios. Development was significantly slower in all the laboratory strains compared to the progeny of forest collected Connecticut females. Progeny production was greater (almost 2X) for the “wild” females and the French-Yugoslavian-Connecticut hybrid than for the laboratory Connecticut strain. The proportion of females collected from the “wild” (Connecticut) strain was higher than that observed in any laboratory strain. A field test was conducted using the triple hybrid in 3 release plots with ca. 6000A. melanoscelus cocoons released per plot in central Connecticut, U.S.A. Weekly collections of gypsy moth larvae showed that the % parasitism was significantly higher in release plots than in the 3 check plots. These results suggest the value of inundative releases ofA. melanoscelus for reduction of sparse gypsy moth populations, but they did not show that hybridization of these strains produced a more effective parasitoid under forest conditions.     

Genome instability in interspecific cell hybrids I. Unstable expression of genes in divergent cell hybrids

Somatic cell hybrids between cells of widely divergent mammalian species display a range of chromosomal and genetic anomalies which may be the equivalent of the “genomic shock” phenomena observed in many plant and animal interspecific hybrids. Mouse-kangaroo hybrids show extreme segregation and fragmentation of the kangaroo chromosomes. Here 1 show that, in addition to the chromosomal instability, some hybrids display unstable expression of three genes borne on the kangaroo active maternal X chromosome. These genes (HPRT, G6PD andPGK) may be co-ordinately inactivated at high frequency, then reactivated once more. I suggest that this reversible inactivation in interspecific hybrids may be the result of an unstable change at an X inactivation centre located in the kangaroo X_q.     

Somatic hybrid plants of Nicotiana x sanderae (+) N. debneyi with fungal resistance to Peronospora tabacina

Background and Aims

The genus Nicotiana includes diploid and tetraploid species, with complementary ecological, agronomic and commercial characteristics. The species are of economic value for tobacco, as ornamentals, and for secondary plant-product biosynthesis. They show substantial differences in disease resistance because of their range of secondary products. In the last decade, sexual hybridization and transgenic technologies have tended to eclipse protoplast fusion for gene transfer. Somatic hybridization was exploited in the present investigation to generate a new hybrid combination involving two sexually incompatible tetraploid species. The somatic hybrid plants were characterized using molecular, molecular cytogenetic and phenotypic approaches.

Methods

Mesophyll protoplasts of the wild fungus-resistant species N. debneyi (2n = 4x = 48) were electrofused with those of the ornamental interspecific sexual hybrid N. × sanderae (2n = 2x = 18). From 1570 protoplast-derived cell colonies selected manually in five experiments, 580 tissues were sub-cultured to shoot regeneration medium. Regenerated plants were transferred to the glasshouse and screened for their morphology, chromosomal composition and disease resistance.

Key Results

Eighty-nine regenerated plants flowered; five were confirmed as somatic hybrids by their intermediate morphology compared with parental plants, cytological constitution and DNA-marker analysis. Somatic hybrid plants had chromosome complements of 60 or 62. Chromosomes were identified to parental genomes by genomic in situ hybridization and included all 18 chromosomes from N. × sanderae, and 42 or 44 chromosomes from N. debneyi. Four or six chromosomes of one ancestral genome of N. debneyi were eliminated during culture of electrofusion-treated protoplasts and plant regeneration. Both chloroplasts and mitochondria of the somatic hybrid plants were probably derived from N. debneyi. All somatic hybrid plants were fertile. In contrast to parental plants of N. × sanderae, the seed progeny of somatic hybrid plants were resistant to infection by Peronospora tabacina, a trait introgressed from the wild parent, N. debneyi.

Conclusions

Sexual incompatibility between N. × sanderae and N. debneyi was circumvented by somatic hybridization involving protoplast fusion. Asymmetrical nuclear hybridity was seen in the hybrids with loss of chromosomes, although importantly, somatic hybrids were fertile and stable. Expression of fungal resistance makes these somatic hybrids extremely valuable germplasm in future breeding programmes in ornamental tobacco.     

Observations on the big bang flowering of Miconia minutiflora (Melastomataceae)

Trees ofMiconia minutiflora produced abundant flowers for only one to three days during mid-April 1983 in the vicinity of Saül, French Guiana. They attracted large numbers of at least 14 species of bees that collected nectar or pollen or both. Nectar production is uncommon in the Melastomataceae and not previously reported forMiconia. Peak bee activity at the trees was in the morning and by afternoon most visits were limited to those bees in search of remnant pollen, especially species ofTrigona. As has been shown for other neotropical plants, heavy rains may trigger flowering in this species. It is suggested that the flowering system ofM. minutiflora promotes outcrossing because of interactions among the numerous species of bees visiting the trees and because of inter-individual variation in nectar and pollen availability. Therefore, bees may fly to other trees instead of becoming satiated with nectar or pollen from a single tree.     

Panicum shastense (gramineae), a sterile hybrid between P. Pacificum and P. Scribnerianum

Natural and synthetic hybrids are reported betweenPanicum, scribnerianum Nash and two other species,P. pacificum Hitchc. & Chase andP. occidentale Scribn. & Merr. The hybrids are morphologically intermediate between the parents, and those in whichP. pacificum is one parent strongly resemble the rareP. shastense Scribn. & Merr. All the parent plants studied cytologically had regular meiosis and a gametic number ofn = 9 chromosomes. The hybrids usually showed good pairing of chromosomes in meiosis, but irregularities such as univalents and lagging chromosomes were common. In the hybrids generally less than 7% of the pollen grains stained with cotton blue in lactophenol, and the plants set no seed, whereas the parent plants generally had over 90% pollen stainability and a high percentage of seed set. Pollen fromP. shastense, like that of the hybrids, was 3–4% stainable.Panicum shastense is believed to be based on a first generation sterile hybrid and the nameP. xshastense is proposed.     

Revision of Dicorynia (Cassieae,Caesalpiniaceae)

A combined taxonomic revision and wood anatomical study ofDicorynia, a South American genus of legumes that is unusual in both its floral and wood anatomy, is presented. Two possible evolutionary pathways leading to the unique 8-to 10-thecate anthers are discussed, and it is concluded that apical proliferation of the thecal primordia is the more likely. Gross and microscopic features of this silica-accumulating wood are given in detail and contrasted with other legume woods especially those containing silica. Economic uses of the trees, especially the wood ofD. guianensis, are discussed particularly in regard to marine construction. It is suggested that the high resistance of this wood to marine borers lies not so much in its silica content as to the presence of some other chemical. Based on the similarity of floral and fruit structures, the number of species is reduced from 7 to 2:D. guianensis in the Guianas andD. paraensis in the Amazonian region. Vegetative variations in the Amazonian population, previously given species rank, are reduced to 5 new varieties ofD. paraensis.     

Chenopodium pumilio in Czechoslovakia: Its strategy of dispersal and domestication

The paper deals with dispersal and domestication ofChenopodium pumilio R. Br. in Czechoslovakia. Tabulated habitats point out the predominant dispersal of this species by various kinds of hemorochory, while autochory, chamaechory, endochory and epichory are other possible means of dispersal. Successfull domestication ofChenopodium pumilio is facilitated by abundance of viable fruits possessing an efficient dormancy mechanism that prevents them germinating in adverse seasons of the year. Naturalization of this species is further supported by prolonged viability of the fruits, and by favourable periodicity of dissemination.