Genetic structure and morphological variation of British populations of the hybrid Potamogeton x salicifolius

Potamogeton x salicifolius Wolfg. is one of the three most frequently recorded Potamogeton hybrids in the British Isles and Europe. It is thought to be the hybrid between P. lucens and P. perfoliatus. Its scattered distribution suggests that it has arisen several times in Britain. Most British populations of P. x salicifolius can be identified by their morphological characteristics, which are intermediate between those of the putative parents P. lucens and P. perfoliatus . However, the population at the Ouse Washes, Cambridgeshire, differs from other populations in its greater similarity to P . lucens . A genetic study of eight British populations, using six isozyme systems, revealed that most populations consist of a single multi-enzyme phenotype. This suggests that they were the result of a single hybridization event and are therefore maintained through vegetative reproduction. By contrast, the Ouse Washes population consists of three multi-enzyme phenotypes. This variation is likely to have resulted from multiple hybridization events, although we cannot exclude the possibility that the plants are partially fertile. The isozyme systems studied were unable to identify P. lucens and P. perfoliatus unambiguously, and consequently did not provide evidence for their putative parentage of P. x salicifolius. However, at a local level the banding patterns of the hybrids were generally consistent with the local multi-enzyme phenotypes of these putative parents.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 144 , 99–111.     

洱海底泥特性对七种沉水植物生长的影响

为研究洱海底泥特性对沉水植物生长的影响,采用不同比例洱海底泥与湖岸土壤掺混形成五种基质,并分别移栽苦草、黑藻、微齿眼子菜、马来眼子菜、光叶眼子菜、穿叶眼子菜和狐尾藻,进行为期70d的室外生长实验,结果表明不同基质对几种植物的影响具种间差异。（1）在基质为50%深层底泥+50%湖岸土壤（碳、氮、磷含量分别为31.59、0.334和0.095 mg/g）时,苦草、马来眼子菜和光叶眼子菜的株高最大;基质为100%深层底泥（碳、氮、磷含量分别为37.88、0.803和0.149 mg/g）时,黑藻、微齿眼子菜、穿叶眼子菜和狐尾藻的株高最大;（2）基质为100%深层底泥时,苦草、黑藻、微齿眼子菜、马来眼子菜和光叶眼子菜生物量增加最多且相对生长速率最大;基质为100%浅层底泥（碳、氮、磷含量分别为77.37、5.691和0.136 mg/g）时,穿叶眼子菜生物量增加最多,相对生长速率最大;狐尾藻在基质为50%浅层底泥+50%深层底泥（碳、氮、磷含量分别为49.27、2.005和0.131 mg/g）时生物量增加最多,相对生长速率最大;（3）基质为100%湖岸土壤（碳、氮、磷含量分别为22.06、0.327和0.231 mg/g）时,7种沉水植物均生长缓慢,生物量增加较少。综上所述,中营养底泥（碳、氮、磷含量分别为31.59-49.27、0.334-2.005和0.095-0.131 mg/g）更适合沉水植物生长,底泥中过高或过低营养都不利于沉水植物生长。     

Heterogeneity of three molecular data partition phylogenies of mints related to M. x piperita (Mentha; Lamiaceae)

Phylogenetic reconstructions with molecular tools are now widely used, thanks to advances in PCR and sequencing technologies. The choice of the molecular target still remains a problem because too few comparative data are available. This is particularly true for hybrid taxa, where differential introgression of genome parts leads to incongruity between data sets. We have studied the potential of three data partitions to reconstruct the phylogeny of mints related to M. x piperita. These included nuclear DNA (ITS), chloroplast DNA (non-coding regions trnL intron, intergenic spacers trnL-trnF, and psbA-trnH), and AFLP and ISSR, markers. The taxonomic sampling was composed of hybrids, diploid and polyploid genomes. Since the genealogy of cultivated mint hybrids is known, they represent a model group to compare the usefulness of various molecular markers for phylogeny inference. Incongruities between ITS, chloroplast DNA, and AFLP-ISSR phylogenetic trees were recorded, although DNA fingerprinting data were congruent with morphological classification. Evidence of chloroplast capture events was obtained for M. x piperita. Direct sequencing of ITS led to biased results because of the existence of pseudogenes. Sequencing of cloned ITS further failed to provide evidence of the existence of the two parental copy types for M. x piperita, a sterile hybrid that has had no opportunity for concerted evolution of ITS copies. AFLP-ISSR data clustered M. x piperita with the parent that had the largest genome. This study sheds light on differential of introgression of different genome regions in mint hybrids.     

Isozyme evidence for hybridization between Potamogeton natans and P. nodosus (Potamogetonaceae) in Britain

A population of pondweeds from the River Stour in Dorset intermediate in morphology between Potamogeton natans L. and P. nodosus Poir. is shown by means of isozyme evidence to be the hybrid P. × schreberi G. Fisch. It is represented by a single multi-enzyme phenotype which, together with its sterility, suggests it reproduces vegetatively and may well constitute a single clone. It is genetically distinct from the morphologically similar hybrid between P. lucens L. and P. natans (P . x fluitans Roth).     

Experimental Hybridization Reveals Biased Inheritance of the Internal Transcribed Spacer of the Nuclear Ribosomal DNA in Begonia ×taipeiensis

Begonia × taipeiensis C.-I Peng, a naturally occurring hybrid resulting from B. formosana × B. aptera, in Taiwan. To understand the inheritance of ribosomal DNA in unidirectional hybridization, experiments were conducted using B. formosana and B. aptera as ovule and pollen donors, respectively. The internal transcribed spacer region (ITS) of nuclear ribosomal DNA was amplified from the artificial hybrids, parental species, and natural hybrids. In contrast to the single type of ITS in the parental species, multiple sequences were cloned from both natural and artificial hybrids. A split decomposition network based on ITS nucleotide variation revealed that all but one (clone B14) of the hybrid sequences were “phylogenetically” closely related to B. formosana. Apparently, in such unidirectional hybridization, maternal DNA provided most of phylogenetic information. In the hybrid sequences, in addition to additive polymorphisms inherited from maternal (38.1%) and paternal (30.1%) plants, a novel nucleotide composition (31.8%) was also detected. The “new” characters are seen as noise in phylogenetic inference. They were probably obtained via intramolecular recombination, as gene conversion was not detected. The occurrence of genetic recombination appeared to be nonrandom, with a higher frequency in the ITS1 (3.14%) and ITS2 (3.42%) regions than in the 5.8S RNA gene (2.22%). Given the lack of sexual recombination in B. × taipeiensis and short time span, unequal crossing-over likely contributed to the heterogeneity of the ITS composition in the nuclear genome. Although the sterile hybrids have not attained their own lineage independent from the parental species, a high level of genetic diversity is transmitted asexually and maintained in these plants. Received 7 February 2001/ Accepted in revised form 31 May 2001     

ent-Labdane glycosides from the aquatic plant Potamogeton lucens and analytical evaluation of the lipophilic extract constituents of various Potamogeton species

Two new ent-labdane glycosides, one known furano-ent-labdane and a new hydroxylated fatty acid were isolated from the dichloromethane extract of the freshwater aquatic plant Potamogeton lucens. The new compounds were assigned the structures of beta-d-glucopyranosyl-8(17),13-ent-labdadien-16,15-olid-18-oate, 18-beta-d-glucopyranosyloxy-8(17),13-ent-labdadien-16,15-olide and 13(R)-hydroxy-octadeca-(9Z,11E,15Z)-trien-oic acid by spectroscopic means. The algicidal activity of these compounds was tested against Raphidocelis subcapitata. Based on our previous study of Potamogeton pectinatus, other constituents were identified in P. lucens by LC-UV-MS, LC-NMR and GC-MS. The lipophilic extract profiles of both species are presented. Two other species, Potamogeton perfoliatus and P. crispus, were also investigated by analytical comparison of their non-polar extracts. The distribution of ent-labdanes characterized in Potamogeton is summarized.     

Genetic diversity and origin of Potamogeton anguillanus (Potamogetonaceae) in Lake Biwa,Japan

We analyzed the genetic variation in Potamogeton anguillanus Koidz. and its putative parents, P. malaianus Miq. and P. perfoliatus L., at five allozyme loci of four enzymes to test the hypothesis of a hybrid origin for P. anguillanus, collected in Lake Biwa, Japan. Alleles diagnostic for either P. malaianus or P. perfoliatus were present at four loci. Of 13 single locus phenotypes (SLPs) of P. anguillanus, eight were phenotypes that were expected in F(1) hybrids between P. malaianus and P. perfoliatus. Two SLPs were different from those expected in F(1) hybrids but could have resulted from segregation of parental alleles in later generation hybrids. Each of the remaining three SLPs possessed one allele unique to P. anguillanus. Allozyme analyses thus supported the view that P. anguillanus was derived from hybridization between P. malaianus and P. perfoliatus. It seems likely that the genetic diversity of P. anguillanus found previously originated through multiple hybridizations and sexual processes in P. anguillanus. Other processes such as intragenic recombination, mutation, or hybridization with another lineage are also discussed with reference to the origin of unique alleles.     

Unidirectional dominance of cytoplasmic inheritance in two genetic crosses of Plasmodium falciparum.

Malarial parasites have two highly conserved cytoplasmic DNA molecules: a 6-kb tandemly arrayed DNA that has characteristics of a mitochondrial genome, and a 35-kb circular DNA that encodes functions commonly found in chloroplasts. We examined the inheritance pattern of these elements in two genetic crosses of Plasmodium falciparum clones. Parent-specific oligonucleotide probes and single-strand conformation polymorphism analysis identified single nucleotide changes that distinguished the parental 6- and 35-kb DNA molecules in the progeny. In all 16 independent recombinant progeny of a cross between a Central American clone, HB3, and a Southeast Asian clone, Dd2, the 6- and 35-kb DNAs were inherited from the Dd2 parent. In all nine independent recombinant progeny of a cross between clone HB3 and a likely African clone, 3D7, the 6-kb DNA was inherited from the 3D7 parent. Inheritance of cytoplasmic genomes of the Dd2 and 3D7 parents was, therefore, dominant over that of the HB3 parent. Cytoplasmic DNA molecules were found almost exclusively in the female gametes of malarial parasites; hence, clone HB3 did not appear to have served as a maternal parent for the progeny of two crosses. Defective differentiation into male gametes by clone Dd2 is likely to be a reason for the cytoplasmic inheritance pattern seen in the HB3 x Dd2 cross. However, incompetence of male or female gametes is unlikely to explain the uniparental dominance in recombinant progeny of the HB3 x 3D7 cross, since both parents readily self-fertilized and completed the malaria life cycle on their own. Instead, the data suggest unidirectional parental incompatibility in cross-fertilization of these malarial parasites, where a usually cosexual parental clone can participate only as a male or as a female. Such an incompatibility may be speculated as indicating an early phase of reproductive isolation of P. falciparum clones from different geographical regions.     

Hybrid rice (Oryza sativa L.): identification and parentage determination by RAPD fingerprinting

Summary DNA from three families of rice plants selected in Northern China (each comprising the male sterile, the restorer, the hybrid F1 and the maintainer lines) has been extracted and amplified by PCR with different random DNA primers (RAPD analysis). Then, DNA has been analysed by agarose gel electrophoresis and DNA bands scored as present or absent. The generated matrices are reproducible and amenable for identification of each single plant line. Thus, RAPD fingerprinting of the inbred parental lines and of the resulting hybrid is proposed as a convenient tool for the identification, protection and parentage determination of plant hybrids. Furthermore, by offering a molecular tool to verify the degree of dissimilarity between the parental lines, the RAPD analysis may also be used to search for new parental combinations.     

Restriction fragment length polymorphisms of a chloroplast photosystem II gene from poplar and their use for species identification.

In a total DNA library from the poplar clone Beaupré (Populus trichocarpa x P. deltoides) one DNA clone was found to identify restriction site polymorphisms in different poplar species. This clone represents a cpDNA gene that shows close homology to a photosystem II gene of pea and spinach coding for the D2 protein and the 44 kDa reaction centre. In Southern blot analysis this probe identified interspecific restriction site variation among the different poplar species; intraspecific variation was not detectable. As the chloroplast genome is maternally inherited in poplars this cpDNA probe was used for identification of P. nigra or P. deltoides as the seed parents of F1 hybrid trees in natural stands of western Germany.     

Internal transcribed spacer repeat-specific primers and the analysis of hybridization in the Glycine tomentella (Leguminosae) polyploid complex

Polyploid and diploid hybridization is a ubiquitous and evolutionarily important phenomenon in the plant world. Determining the parental species of a hybrid, however, is difficult. Molecular markers such as the nuclear ribosomal DNA gene complex, particularly its internal transcribed spacer (ITS) region, have proved powerful in determining hybrid parentage. In some cases, population and genomic phenomena, such as genetic drift and concerted evolution, result in the loss of all or many of the tandemly repeated copies derived from one parental species, making the recovery of hybrid history difficult or impossible. Methods such as direct sequencing and cloning are typically used to find ITS sequences contributed from parental species, but are limited in their ability to detect rare repeat types. Here we report that repeat-specific polymerase chain reaction primers can recover rare parental ITS sequences in the Glycine tomentella polyploid complex. In three allopolyploid lineages of this complex, repeat-specific primers reliably detected rare repeats that both direct sequencing and the screening of many cloned sequences failed to detect. Other strategies, such as the use of exclusion primers, may detect rare parental repeat types in hybrids when previous hypotheses regarding the second parental species are lacking.     

Genomic Characterization of Interspecific Hybrids between the Scallops Argopecten purpuratus and A. irradians irradians

The Peruvian scallop (Argopecten purpuratus) has been introduced to China and has successfully been hybridized with the bay scallop (A. irradians irradians). The F1 hybrids of these two scallops exhibited a large increase in production traits and some other interesting new characteristics. To understand the genetic basis of this heterosis, nuclear gene and partial mtDNA sequences, and genomic in situ hybridization (GISH) were employed to analyze the genomic organization of the hybrids. Amplification of the ribosomal DNA internal transcribed spacer (ITS) showed that the parental ITS sequences were present in all the hybrid individuals, illustrating that the hybrid offspring inherited nuclear DNA from both parents. Sequence analyses of the ITS region further confirmed that the hybrids harbored alleles from their parents; some recombinant variants were also detected, which revealed some alterations in the nuclear genetic material of the hybrids. The analysis of mitochondrial 16S rDNA showed that the hybrids possessed sequences that were identical to the 16S rDNA of the female parents, proving a matrilineal inheritance of mitochondrial genes in scallops. In addition, GISH clearly discriminated between the parental chromosomes and indicated a combination of haploid genomes of duplex parents in the hybrids. The genetic analyses in our study illustrated that the F1 hybrids inherited nuclear material from both parents and cytoplasmic genetic material maternally, and some variations occurred in the genome, which might contribute to a further understanding of crossbreeding and heterosis in scallop species.     

Attached bacterial populations shared by four species of aquatic angiosperms

Symbiotic relationships between microbes and plants are common and well studied in terrestrial ecosystems, but little is known about such relationships in aquatic environments. We compared the phylogenetic diversities of leaf- and root-attached bacteria from four species of aquatic angiosperms using denaturing gradient gel electrophoresis (DGGE) and DNA sequencing of PCR-amplified 16S rRNA genes. Plants were collected from three beds in Chesapeake Bay at sites characterized as freshwater (Vallisneria americana), brackish (Potomogeton perfoliatus and Stuckenia pectinata), and marine (Zostera marina). DGGE analyses showed that bacterial communities were very similar for replicate samples of leaves from canopy-forming plants S. pectinata and P. perfoliatus and less similar for replicate samples of leaves from meadow-forming plants Z. marina and V. americana and of roots of all species. In contrast, bacterial communities differed greatly among plant species and between leaves and roots. DNA sequencing identified 154 bacterial phylotypes, most of which were restricted to single plant species. However, 12 phylotypes were found on more than one plant species, and several of these phylotypes were abundant in clone libraries and represented the darkest bands in DGGE banding patterns. Root-attached phylotypes included relatives of sulfur-oxidizing Gammaproteobacteria and sulfate-reducing Deltaproteobacteria. Leaf-attached phylotypes included relatives of polymer-degrading Bacteroidetes and phototrophic Alphaproteobacteria. Also, leaves and roots of three plant species hosted relatives of methylotrophic Betaproteobacteria belonging to the family Methylophilaceae. These results suggest that aquatic angiosperms host specialized communities of bacteria on their surfaces, including several broadly distributed and potentially mutualistic bacterial populations.     

Identification of the polar constituents of Potamogeton species by HPLC-UV with post-column derivatization, HPLC-MSn and HPLC-NMR, and isolation of a new ent-labdane diglycoside

The polar extracts of Potamogeton pectinatus, P. lucens, P. perfoliatus and P. crispus (Potamogetonaceae) were analyzed by HPLC-UV-MS and their chromatographic profiles were very similar. The polar constituents of P. pectinatus were more exhaustively investigated by HPLC-UV with post-column derivatization, HPLC-MS(n) and HPLC-NMR, which allowed the on-line identification of various known flavones (dereplication). One of these compounds, luteolin 3'-O-glucoside, has never been characterized in the Potamogeton genus. The HPLC-UV-MS and HPLC-NMR analyses revealed also the presence of ent-labdane diterpene glycosides in the polar extracts of P. pectinatus and P. lucens and led to the isolation of a new ent-labdane diglycoside from P. pectinatus, beta-D-glucopyranosyl-(1-->2)-beta-D-glucopyranosyl-15,16-epoxy-12-oxo-8(17),13(16),14-ent-labdatrien-19-oate.     

ITS sequence variation and concerted evolution in the natural hybrid species Malus toringoides

The internal transcribed spacer (ITS) region of nuclear ribosomal DNA (nrDNA) is one of the most used molecular characters in plant systematics. Our previous studies based on morphological analysis and ITS sequence variation suggested that Malus toringoides (Rehd.) Hughes is derived from hybridization between M. transitoria (Batal.) Schneid. and M. kansuensis (Batal.) Schneid. To further understand the variation pattern of ITS sequences in M. toringoides, and to elucidate the evolutionary processes that affect ITS sequence variation after hybridization, we sampled 99 accessions from multiple populations of the hybrid and parental species, and then obtained totally 254 ITS sequences by cloning and sequencing. Our ITS variation data demonstrates three outcomes of ITS repeats after hybrid speciation. ～ 27–41% of M. toringoides have only M. transitoria type ITS sequence, ～ 40–70% have M. transitoria type ITS sequence plus one or two chimeric ITS sequences generated by recombination between parental ITS sequences, and six accessions retain both parental type ITS sequences. The plausible evolutionary processes that created the observed ITS variations were inferred to be the joint actions of recombination, concerted evolution, pseudogenization and backcrossing. Our study provides further understandings of the variation model of ITS repeats after hybridization as well as the evolution of M. toringoides after its hybrid speciation.     

Somatic hybridization between birdsfoot trefoil (Lotus corniculatus L.) and L. conimbricensis Willd

Summary Somatic hybrid plants were produced by fusion of birdsfoot trefoil (Lotus corniculatus) cv Leo and L. conimbricensis Willd. protoplasts. Birdsfoot trefoil etiolated hypocotyl protoplasts were inactivated with iodoacetate to inhibit cell division prior to fusion with L. conimbricensis suspension culture protoplasts. L. conimbricensis protoplasts divided to form callus which did not regenerate plants. Thus, plant regeneration from protoplast-derived callus was used to tentatively identify somatic hybrid cell lines. Plants regenerated from three cell lines exhibited additive combinations of parental isozymes of phosphoglucomutase, and L. conimbricensis-specific esterases indicating that they were somatic hybrids. The somatic chromosome number of one somatic hybrid was 36. The other somatic hybrid exhibited variable chromosome numbers ranging from 33 to 40. These observations approximate the expected combination of the birdsfoot trefoil (2n=4x=24) and L. conimbricensis (2n=2x=12) genomes. Somatic hybrid flowers were less yellow than birdsfoot trefoil flowers and had purple keel tips, a trait inherited from the white flowered L. conimbricensis. Somatic hybrids also had inflorescence structure that was intermediate to the parents. Fifteen somatic hybrid plants regenerated from the three callus lines were male sterile. Successul fertilization in backcrosses with birdsfoot trefoil pollen has not yet been obtained suggesting that the hybrids are also female sterile. This is the first example of somatic hybridization between these two sexually incompatible Lotus species.Formerly USDA-ARS, St. Paul, Minn, USA     

Phylogenetics and reticulate evolution in Pistacia (Anacardiaceae)

The systematic position and intrageneric relationships of the economically important Pistacia species (Anacardiaceae) are controversial. The phylogeny of Pistacia was assessed using five data sets: sequences of nuclear ribosomal ITS, the third intron of the nuclear nitrate reductase gene (NIA-i3), and the plastid ndhF, trnL-F and trnC-trnD. Significant discordance was detected among ITS, NIA-i3, and the combined plastid DNA data sets. ITS, NIA-i3, and the combined plastid data sets were analyzed separately using Bayesian and parsimony methods. Both the ITS and the NIA-i3 data sets resolved the relationships among Pistacia species well; however, these two data sets had significant discordance. The ITS phylogeny best reflects the evolutionary relationships among Pistacia species. Lineage sorting of the NIA-i3 alleles may explain the conflicts between the NIA-i3 and the ITS data sets. The combined analysis of three plastid DNA data sets resolved Pistacia species into three major clades, within which only a few subclades were supported. Pistacia was shown to be monophyletic in all three analyses. The previous intrageneric classification was largely inconsistent with the molecular data. Some Pistacia species appear not to be genealogical species, and evidence for reticulate evolution is presented. Pistacia saportae was shown to be a hybrid with P. lentiscus (maternal) and P. terebinthus (paternal) as the parental taxa.     

Analysis of somatic hybrids between two sterile dihaploid Solanum tuberosum L. breeding lines. Restoration of fertility and complementation of G. pallida Pa2 and Pa3 resistance

Fourteen somatic hybrids generated by electrofusion of mesophyll protoplasts from a non-flowering dihaploid S. tuberosum clone, DHAK-11, and a male-sterile dihaploid clone S. tuberosum, DHAK-33, were grown in the greenhouse and subjected to morphological assessments and tests for fertility and resistance to the white potato cyst nematode Globodera pallida pathotypes Pa2 and Pa3. The ploidy level of the hybrids ranged from 38 to 63 chromosomes. All hybrids developed flowers with violet petals except for one, hy-56, that possessed red petals. The colour of the tuber skin was purple in all hybrids except in hy-56 where the tuber skin was red. All of the hybrids were female fertile and generated viable seeds. Near-tetraploid hybrids produced the highest number of seeds per fruit and these seeds had a normal size. Hybrids with 58 or more chromosomes produced smaller seeds and less seeds per fruit. The germination frequency of the seeds was not influenced by the chromosome number of the hybrids. Pollen viability was determined and the male fertility of three hybrids was tested. Pollination with these three hybrids gave rise to fruit development, but only one produced viable seeds. The hybrids were tested for resistance to G. pallida pathotypes Pa2 and Pa3. A high level of resistance to Pa3, inherited from one parental clone, DHAK-11, and a high level of resistance to Pa2, inherited from the other parental clone, DHAK-33, was combined in four hybrids. These results demonstrate, that protoplast fusion is an efficient method for restoring the fertility of somatic hybrids generated from sterile parent clones, and is a powerful procedure for the complementation of multigenetic disease resistance traits in potato breeding lines.     

Rapd fingerprinting of diploid Lolium perenne × hexaploid Festuca arundinacea hybrid genomes

We tested the application of RAPD technology for identification of hybrid genomes originated from a maternal clone of Lolium perenne L. (2n = 2x = 14) bearing cytoplasmic male sterility, which was pollinated separately by five clones of Festuca arundinacea Schreb. cv. Barocco (2n = 6x = 42). Six classes of RAPD markers were recognized, specific to: 1) Festuca genome and inherited into F1 hybrid genomes, 2) Lolium genome inherited into F1 hybrid genomes, 3) Lolium-specific bands not found in F1 progeny, 4) Festuca-specific bands not found in F1 progeny, 5) new bands found only in F1 hybrid profiles, 6) bands common to all parental and F1 hybrid genotypes. RAPD data were shown to have full potential a) to serve as an unequivocal proof of genome recombination in perennial ryegrass × tall fescue hybrids, b) to identify hybrid genomes, c) to reveal phenetic relationships of the accessions from crossing families, d) to enhance, by fingerprinting, the selection of superior hybrid material for further breeding. RAPD data were found to be consistent with the festucoid phenotype of F1 hybrids. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterisation of thermotolerant Saccharomyces cerevisiae hybrids

Thermotolerant Saccharomyces strains were crossed with mesophilic Saccharomyces cerevisiae and with cryotolerant Saccharomyces bayanus. The former hybrid is fertile confirming thermotolerant strains as S. cerevisiae. The spores from this hybrid, though, possess a low germinability and give cultures that grow poorly. The hybrid cryotolerant x thermotolerant is sterile and show a new combination of the parental strains' traits improving their technological application. © Rapid Science Ltd. 1998