Presumed Hybrid Research Articles

Atlas Florae Europaeae notes, 33. Taxonomic synopsis of East European species of the Cytisusratisbonensis group (Fabaceae).

A group of species of Cytisussect.Tubocytisus with strictly lateral inflorescences, commonly referred to as C.ratisbonensis s.l., is critically revised in Eastern Europe on the basis of morphology and comprehensive treatment of herbarium specimens and observations. Seven species and two presumed hybrids are recognised. Complete accounts are provided for each species, with synonyms, typifications, brief morphological descriptions, data on ecology and distributions, taxonomic and nomenclatural annotations. Cytisuspolonicus is described as new to science, separated from C.ratisbonensis on the basis of morphology and diploid (vs. tetraploid) chromosome count. The lectotype of C.elongatus is superseded and a new lectotype is designated; this name has priority for the species previously known as C.triflorus. Six species names are newly placed to the synonymy: Chamaecytisuspineticola under Cytisusruthenicus s. str., and Cytisusczerniaevii, C.leucotrichus, C.lindemannii, C.ponomarjovii and Chamaecytisuskorabensis under Cytisuselongatus. The presumed hybrid between C.ruthenicus and C.elongatus, which was incorrectly known as C.czerniaevii, is described here as C.semerenkoanus. Cytisuslithuanicus, which has been an obscure name since its original publication, is resurrected for a newly-recognised octoploid species, which is endemic to eastern Poland, western Belarus and north-western Ukraine. The name C.cinereus is re-instated for the species previously known as C.paczoskii, and C.horniflorus is added to its synonymy; its complete distribution area is circumscribed, and its occurrence in Austria, Poland, Romania, Serbia and Slovakia is documented. Cytisuskreczetoviczii and C.elongatus are reported for the first time from Belarus, and the latter species also from Bosnia and Herzegovina, Montenegro and Slovenia. Cytisusborysthenicus and C.elongatus are reported as new to some territories in European Russia. Cytisusratisbonensis s. str. is treated as absent from Eastern Europe. The neglected protologue of C.ruthenicus is discovered, and the nomenclature of all other names is verified and corrected when necessary. The original material of C.borysthenicus is re-discovered. Five further lectotypes and one neotype are designated. Distribution areas are circumscribed on the basis of numerous herbarium collections and documented observations, identified or verified by the authors. Chromosome counts published for nameless taxa from Belarus, Ukraine and Russia are assigned to the species according to their herbarium vouchers: C.borysthenicus, C.kreczetoviczii and C.lithuanicus are octoploid (2n = 100), C.ruthenicus is tetraploid (2n = 50) and octoploid (2n = 100), and C.semerenkoanus and C.elongatus are tetraploid (2n = 50).

Clarifying genetic and taxonomic relationships among Pistacia taxa (Anacardiaceae) in Croatia

In the eastern Adriatic flora the genus Pistacia L. (Anacardiaceae) is represented with P. lentiscus L., P. terebinthus L., their hybrid P. × saportae Burnat and the cultivated P. vera L. In addition, an endemic putative taxon from Mt. Biokovo was described in 1985 as P. calcivora Radić. Our aim was to resolve relationships between the four putative indigenous taxa of this genus in Croatia (P. lentiscus, P. terebinthus, P. × saportae and P. calcivora) based on genetic (AFLP) and morphological data. Specifically, we aimed to determine the presence of the hybrid taxon P. × saportae and to validate the controversial taxonomic status of P. calcivora at the molecular and morphological levels. Our combined results indicate the presence of two well separated groups of populations. The first group included all individuals of P. terebinthus and the individuals initially assigned to the potential taxon P. calcivora based on leaf morphology, suggesting that there is no support for the described taxon P. calcivora and that it should be considered as a synonym for P. terebinthus. The second group corresponded to P. lentiscus and included the majority of the presumed hybrid individuals of P. × saportae. However, four hybrid individuals were confirmed at the molecular level and were placed between the two parental taxa in the phylogenetic tree, confirming the presence of P. × saportae in Croatia. Although confirmed P. × saportae individuals were genetically closer to P. lentiscus, they were morphologically more similar to P. terebinthus, hindering their correct identification in the field.

A crowd-sourced genomic project to assess hybrid content in a rare avian vagrant (Azure Tit Cyanistes cyanus (Pallas, 1770))

The aim of this study was to correlate plumage variation with the amount of genomic hybrid content in hybrids between Azure Tits Cyanistes cyanus (Pallas, 1770) and European Blue Tit Cyanistes caeruleus (Linnaeus, 1758), by re-sequencing the genomes of museum specimens of non-hybrids and presumed hybrids with varying plumages. The project was funded by crowdsourcing and initiated when two presumed Azure Tits, observed by hundreds of Swedish birdwatchers, were rejected as hybrids based on minor plumage deviations assumed to indicate hybrid contents from the European Blue Tit. The results confirm that hybrids with intermediate plumages, so called Pleske’s Tits, are first generation hybrids (F1 hybrids). Individuals, whose plumages are similar to Azure Tits, but assessed as hybrids based on minor plumage deviations, are all backcrosses but vary in their degree of hybrid content. However, some individuals morphologically recognized as pure Azure Tits expressed similar degrees of hybrid content. The results indicate that: (1) hybrid content may be widespread in Azure Tits in the western part of its habitat distribution; (2) plumage deviation in backcrosses is not linearly correlated with the genetic degree of hybrid origin; and (3) all Azure Tits observed in Europe outside its natural distribution may have some degree of hybrid origin. We therefore suggest that it is very difficult to phenotypically single out hybrids beyond first generation backcrosses. We argue that decreased sequencing costs and improved analytical tools open the doors for museomic crowd-sourced projects that may not address outstanding biological questions but have a major interest for lay citizens such as birdwatchers.

Mixed-species association and a record of a hybrid offspring between Trachypithecus pileatus and Trachypithecus phayrei in Bangladesh

The term mixed-species association has a broad range of definitions, from temporary foraging association to permanent group living. A mixed-species association mostly involves species from closely related taxa and is found in birds, mammals and fish. It ranges from passive association with little interaction to coordinated behavioural interactions between the group members of a mixed-species group. Mixed-species association can result in the production of hybrid offspring in the wild. In this study, we present, to the best of our knowledge, the first observational evidence of mixed-species association between the two threatened primate species Phayre’s langur (Trachypithecus pileatus) and capped langur (Trachypithecus phayrei), in fragmented forest patches of northeast Bangladesh. We also report a presumed hybrid offspring between these species. We conducted a short-term study from December 2021 to April 2022 in three forest patches based on information from eco-tourism guides. We confirmed the presence of three mixed-species troops; in two of the groups an adult male T. phayrei had permanently immigrated into a group of T. pileatus, and in the other one an adult male T. pileatus had permanently immigrated into a group of T. phayrei. A long-term detailed study is needed to elucidate the reasons for these mixed-species associations, their behavioural patterns, the fate of the presumed hybrid offspring, and to understand the genetic relatedness between the individuals.

The distribution and biogeography of slow worms (Anguis, Squamata) across the Western Palearctic, with an emphasis on secondary contact zones

Abstract The slow-worm lizards (Anguis) comprise five species occurring throughout most of the Western Palearctic. Although these species are relatively uniform morphologically – with the exception of A. cephallonica, which exhibits a quite unique morphology – they are genetically deeply divergent. Here, we provide detailed distribution maps for each species and discuss their biogeography and conservation based on updated genetic data and a robust distribution database. We pay particular attention to the so called ‘grey zone’, which typically represents secondary contact zones and in some cases confirmed or presumed hybrid zones. Four of the five species live in parapatry, while only two species, A. cephallonica and A. graeca from the southern Balkans occur in partial sympatry. Further research should focus on the eco-evolutionary interactions between species in contact, including their hybridization rates, to reveal deeper details of the slow-worm evolutionary and natural history.

Composition, size distribution, length-weight relationship of sympatric mud crab species (Scylla) and the case of presumed hybrids

Multiple species of mud crabs are known to co-exist sympatrically within the same ecosystem. However, little is known about the potential factors influencing their community composition. In addition, four types of presumed hybrids (SH 1–4) of the genus Scylla with distinct variations in morphological and morphometric characters were reported recently at Kota Marudu Mangrove Forest, Sabah, Malaysia. Therefore, this study described the species composition and investigated the potential species composition-regulating factors of mud crabs in Kota Marudu Mangrove Forest, Sabah, Malaysia. Further, the size distribution, length-weight relationships, and Fulton's condition factors (Ks) of Scylla species, including S. olivacea, S. tranquebarica, S. paramamosain and presumed hybrid SH 1 were also estimated and compared. Interchanging distribution patterns were observed between the two dominating species – S. paramamosain and S. tranquebarica. Interestingly, all four presumed hybrids were only found in September and October 2012. Poisson regression showed that species, sex, and sampling period were influencing factors of Scylla's composition variation. In terms of size, S. tranquebarica was the heaviest and the largest amongst other species. Based on their length-weight relationships, females exhibited negative allometry whereas males showed positive allometry, except S. olivacea males due to their low sampling size. The K values were similar among species and sexes, except S. tranquebarica females with significantly lower mean K values. The results of this study contribute towards the understanding of the relationship between sympatric Scylla species and provide a basis for future hybrid confirmation studies. The description of length-weight relationships and K values of each Scylla species and group serves as essential baseline data for future fisheries management.

Hybridization between Asclepias purpurascens and Asclepias syriaca (Apocynaceae): A cause for concern?1

Rare plant species can be at risk of hybridization, reduced genetic variation, and genetic assimilation when a numerically abundant congener co-occurs in or invades their habitat. We investigated hybridization between a species in decline, Asclepias purpurascens L., and its common and widespread congener, Asclepias syriaca L. A total of 40 morphological traits were measured on 60 flowering plants from a mixed population in Connecticut. Cluster and principal component analyses identified two distinct clusters of parental species taxa and a third cluster representing putative hybrids. Although leaf traits of putative hybrids were more similar to A. syriaca, floral traits and the morphological space on the principal component analysis were more similar to A. purpurascens. This suggests that the population contains a mix of F1 and advanced generation hybrids with the possibility of introgression into A. purpurascens. Although putative hybrids are intermediate for most traits, pollen counts reveal reduced fertility of presumed hybrid that might influence mating behaviors and increase the likelihood of backcrossing with A. purpurascens. We suggest a combination of morphological traits that better identify the two parental species as well as hybrids in the field. Conservationists should consider options of managing A. syriaca where A. purpurascens needs protection from competition to prevent genetic assimilation of the latter.

Fine mapping of a locus presumably involved in hybrid inviability (HIs-1) between flowering cherry cultivar Cerasus × yedoensis 'Somei-yoshino' and its wild relative C. spachiana.

Flowering cherry is an extremely renowned ornamental tree, consisting of a variety of species and cultivars. Because cherry species have no strict barriers for interspecific hybridization before fertilization, identification of the gene underlying post-zygotic hybrid inviability will help breeders identify specimens for breeding and help us understand speciation mechanisms. In this study, we mapped the genetic linkages and physical genome sequences for a presumed hybrid inviability locus (HIs-1) that we observed in the seedlings crossed between Cerasus × yedoensis ‘Somei-yoshino’ and its wild relative C. spachiana. By the surveying linkage maps of ‘Somei-yoshino’ and C. spachiana, we identified correlation with seedling inviability only in linkage group 4 (LG4) of the ‘Somei-yoshino’ map. When we produced a finer-scaled map of HIs-1 in LG4, we found that HIs-1 is located between two microsatellite (SSR) markers with a 3.8 cM span. Using eight SSR markers based on peach genome sequences, we further refined the candidate region for HIs-1. This region was located between Pp04C001 and Pp04C007 markers, spanning 240 Kb of the peach genome, in which 45 transcribed genes had been estimated. From these candidate genes, it will be feasible to identify molecular mechanisms involved in cherry hybrid inviability.

Revision of Muhlenbergia (Poaceae, Chloridoideae, Cynodonteae, Muhlenbergiinae) in Peru: classification, phylogeny, and a new species, M.romaschenkoi.

A taxonomic treatment, phylogeny based on analysis of six DNA sequence markers (ITS, ndhA intron, rpl32-trnL, rps3, rps16 intron and rps16-trnK) and classification of Muhlenbergia for Peru is given. Seventeen species and one presumed hybrid are recognised. Muhlenbergiaromaschenkoisp. nov. is newly described from the Río Huallaga Valley, northeast of Huánuco. The type of Podosemumangustatum [≡ Muhlenbergiaangustata] clearly aligns with what we had been referring to as the hybrid between this species and M.rigida. Therefore, we adopt the next available heterotypic name, Muhlenbergiacoerulea, for what we had been calling M.angustata and change the hybrid designation to M.coerulea × M.rigida. Lectotypes are designated for Epicampescoerulea Griseb., Muhlenbergiaaffinis Trin., Muhlenbergiaberlandieri Trin., Muhlenbergiabeyrichiana Kunth, Muhlenbergiaelegansvar.atroviolacea Kuntze, Muhlenbergiaelegansvar.subviridis Kuntze and Muhlenbergiaphragmitoides Griseb.

First record of non-native hybrid catfish Pseudoplatystoma reticulatum× Leiarius marmoratus in the Upper Paraná River basin, Brazil.

The aim of this study is to report the presence of a three non-native hybrid long-whiskered catfishes (family Pimelodidae) in the Upper Paraná River basin, Brazil. Genetic analyses demonstrated that the three presumptive hybrids were a result of the crossbreeding of Pseudoplatystoma reticulatum (central Amazonas River basin and Lower Paraná River) and Leiarius marmoratus (Amazonas, Essequibo and Orinoco rivers), producing a hybrid commonly known in Brazil as cachandiá. The potential threat to biodiversity, due to possible genetic contamination, competition and predation of wild stocks, of such artificially produced hybrid fishes is discussed.

Characterization of interspecific hybrids of Petunia and Calibrachoa by multiplex PCR, DNA content, and chromosome number

ABSTRACTPetunia and Calibrachoa are ornamental plants of worldwide economic importance. Commercially, it is useful to combine desirable characteristics of Calibrachoa, including the large diversity of flower colors, with the pH tolerance and vigorous growth of Petunia. For investigation of interspecific hybrids between Petunia and Calibrachoa we used four different introns with flanking exon areas, each from a different gene and with a different sequence for Petunia and Calibrachoa, as genus-specific markers for chromosomes in interspecific hybrids. PCR primers specific for Petunia and Calabrachoa were made from the determined sequences and tested on a range of presumed hybrids using multiplex PCR, which confirmed that the hybrids were derived from these two species. Flow cytometry demonstrated that the hybrids were triploid, and determination of chromosome numbers showed that two of the chromosome sets were from Calibrachoa, i.e. that the other parent, Petunia, was diploid. Similar methods can be used for molecular characterization of other new hybrids made between closely related species or cultivars.

Resolving incongruence: Species of hybrid origin in Columnea (Gesneriaceae)

Speciation by hybridization has long been recognized among plants and includes both homoploid and allopolyploid speciation. The numbers of presumed hybrid species averages close to 11% and tends to be concentrated in a subset of angiosperm families. Recent advances in molecular methods have verified species of hybrid origin that had been presumed on the basis of morphology and have identified species that were not initially considered hybrids. Identifying species of hybrid origin is often a challenge and typically based on intermediate morphology, or discrepancies between molecular datasets. Discrepancies between data partitions may result from several factors including poor support, incomplete lineage sorting, or hybridization. A phylogenetic analysis of species in Columnea (Gesneriaceae) indicated significant incongruencies between the cpDNA and nrDNA datasets. Tests that examined whether one or both of the datasets had the phylogenetic signal to reject the topology of the alternate dataset (Shimodaira and Hasegawa [SH] and approximately unbiased [AU] tests) indicated significant differences between the topologies. Splitstree analyses also showed that there was support for the placement of the discrepant taxa in both datasets and that the combined data placed the putative hybrid species in an intermediate position between the two datasets. The genealogical sorting index (GSI) implied that coalescence in nrDNA had occurred in all species where more than a single individual had been sampled, but the GSI value was lower for the cpDNA of most of the putative hybrids, implying that these regions have not yet coalesced in these lineages despite being haploid. The JML test that evaluates simulated species pairwise distances against observed distances also implies that observed nrDNA data generate shorter distances than simulated data, implying hybridization. It is most likely that C. gigantifolia, C. rubriacuta, and C. sp. nov. represent a lineage from a hybrid ancestor, but C. moorei may be a more recent hybrid and may still be undergoing hybridization with sympatric species.

Genetic characterization of Amur sturgeon Acipenser schrenckii and its hybrid caught around Hokkaido

Genetic characterization was performed in five individuals of wild Amur sturgeon Acipenser schrenckii, and/or its presumed hybrid caught around Hokkaido, using a mitochondrial DNA (mtDNA) marker and two markers of nuclear DNA (nDNA). Genetic analyses indicated that two of the five fish had the mtDNA haplotype of Kaluga, Huso dauricus, whereas the nDNA markers indicated signs for both A. schrenckii and H. dauricus genotypes, referring to a hybrid origin. The other three fish were plausibly pure A. schrenckii. The results indicated the importance of combined usage of mtDNA and nDNA markers for correct species identification in sturgeon.

Taxonomic and geographic differentiation of Pinus mugo complex on the needle characteristics

The phenotypic differentiation of Pinus mugo complex was verified using 31 populations of P. mugo sensu stricto, 11 of P. uncinata, five of P. uliginosa, one of the potential hybrids P. uliginosa × P. mugo and three of P. sylvestris, the latter as a control. The 22 morphological and anatomical needle characteristics were measured and statistically examined to describe the taxa and the population within the taxa differentiation. All the taxa of the P. mugo complex differed significantly from P. sylvestris in most of the verified needle characteristics. Within P. mugo complex, populations of P. uncinata were clearly distinguished from P. mugo s. s. The population of potential hybrid origin was the most similar to P. uliginosa. Populations of the latter taxon were strongly differentiated; some of them were closer to P. uncinata, and others to P. mugo s. s. Within the whole sampled data, three geographic groups of populations were detected: the first included P. uncinata and two of P. uliginosa, the second contained East and South Carpathian P. mugo s. s. with the presumed hybrid population, and the third contained all the other populations of P. mugo s. s. and P. uliginosa. Within P. mugo s. s., the Sudetan populations formed a separate group. Pinus uncinata from the Pyrenees reflected a high level of differentiation. The marginal populations of this taxon (Cebollera, Gúdar, Massif Central) also differed from those in the Pyrenees. The phenotypic differentiation of taxa and populations appeared similar to that which was detected based on cpDNA markers.

Nouveautés dans le Genre Huperzia Bernh. (Lycophytes, Lycopodiaceae) à Madagascar

Abstract Rakotondrainibe, F. & A. Jouy (2015). Novelties in the genus Huperzia Bernh. (Lycophytes, Lycopodiaceae) from Madagascar. Candollea 70:49–56. In French, English and French abstracts. Within the context of the revision of Lycopodiaceae from Madagascar, two new species, Huperzia ambrensis Rakotondr. and Huperzia teretirigida Rakotondr., are described and illustrated. Two new synonyms are also proposed: Huperzia hildebrandtii (Herter) Tardieu is a synonym of Huperzia squarrosa (G. Forst.) Trevis. and Huperzia rubrica (Herter) Tardieu is a synonym of Huperzia ophioglossoides (Lam.) Rothm. A presumed hybrid, Huperzia megastachya (Baker) Tardieu × Huperzia squarrosa (G. Forst.) Trevis., is described and compared with its putative parents.

Variation Patterns of the Volatile Compounds in Flowers of Chinese Native Citrus Species and Their Taxonomic Implications

In this study, the volatile compounds in the flowers of nine Citrus species/varieties, seven of which are native to China, were analyzed using headspace-solid phase microextraction (HS-SPME) coupled with gas chromatography mass spectrometry (GC-MS). A total of 94 compounds were identified, including various terpenes, such as monoterpenes, sesquiterpenes, terpene alcohols and aldehydes, which together accounted for 80.4% to 92.4% of the total compounds analyzed. Limonene, linalool and γ-terpinene were the dominant terpenes. Different species/varieties were characterized by their volatile compounds. Papeda was characterized by a high level of β-ocimene, linalyl acetate, myrcene and neo-alloocimene; Citrophorum was characterized by a high level of limonene and caryophyllene, and Cephelocitrus by a high level of limonene, β-pinene and linolool. Sinocitrus had the highest amount of linolool. Sweet orange had the highest level of limonene, while sour orange was distinct from others with the highest level of γ-terpinene. The four basic types of the genus <i>Citrus</i> L., Papeda, Cephalocitrus, Citrophorum and Sinocitrus, can be clearly classified based on a cluster analysis of their volatile compounds. All of the presumed hybrid species, including Jinchengbeibei 447 (<i>C. sinensis</i> Osb.), Goutoucheng (<i>C. aurantium</i> L.), Ningmeng 4 (<i>C. limon</i> Burm.f.), and Changshanhuyou (<i>C. paradisi</i> cv. Changshanhuyou), were grouped closely together with a suggested parent species in the constructed dendrogram. Our study clearly demonstrates that Citrus flower volatile compounds and their variation patterns can be used for Citrus species identification and taxonomic study.

Variation patterns in natural populations of wild potatoes along Quebrada de Inca Cueva, northwestern Argentina

Wild potato species, Solanum infundibuliforme Phil. (ifd) (2n = 2x = 24), S. gourlayi Hawkes (grl) (2n = 4x = 48) and presumed grl–ifd hybrids (2n = 4x = 48) were collected from a narrow gorge known as Quebrada de Inca Cueva, located in Jujuy province, Argentina. To explore the possibility of gene flow and introgression within and between populations and ploidy levels, accessions collected in this gorge and others from neighboring valleys, identified as Solanum oplocense Hawkes (opl), grl and ifd, were characterized according to chromosome number, morphological characters, pollen–pistil relations and seed set following controlled diallelic crosses. Multivariate analysis for 36 morphological characters recorded in individual plants revealed considerable variability. Principal coordinates analysis, revealed that tetraploid populations belonging to presumed hybrids and grl formed a huge swarm in which individuals from different populations appeared intermixed. In one accession (ClI 1715), variation in morphological phenotypes in diploid and tetraploids plants were detected, as well as individuals with intermediate characters between the putative parents. The crossing results revealed the action of postzygotic barriers between ifd and presumed hybrids as well as between ifd–opl and grl–opl. These barriers were incomplete as normal seeds were obtained in certain genotypic combinations. In intraspecific crosses and grl × presumed hybrids crosses, pollen tubes grew normally to the base of the style producing fruits with a variable number of seeds in each. The breeding strategy of these species has resulted in complex mixtures of parental genotypes, advanced hybrid generations and backcrosses in this gorge. The implications of these results for germplasm conservation are discussed.

Parallel tagged amplicon sequencing of transcriptome‐based genetic markers for Triturus newts with the Ion Torrent next‐generation sequencing platform

Next-generation sequencing is a fast and cost-effective way to obtain sequence data for nonmodel organisms for many markers and for many individuals. We describe a protocol through which we obtain orthologous markers for the crested newts (Amphibia: Salamandridae: Triturus), suitable for analysis of interspecific hybridization. We use transcriptome data of a single Triturus species and design 96 primer pairs that amplify c. 180 bp fragments positioned in 3-prime untranslated regions. Next, these markers are tested with uniplex PCR for a set of species spanning the taxonomical width of the genus Triturus. The 52 markers that consistently show a single band of expected length at gel electrophoreses for all tested crested newt species are then amplified in five multiplex PCRs (with a plexity of ten or eleven) for 132 individual newts: a set of 84 representing the seven (candidate) species and a set of 48 from a presumed hybrid population. After pooling multiplexes per individual, unique tags are ligated to link amplicons to individuals. Subsequently, individuals are pooled equimolar and sequenced on the Ion Torrent next-generation sequencing platform. A bioinformatics pipeline identifies the alleles and recodes these to a genotypic format. Next, we test the utility of our markers. baps allocates the 84 crested newt individuals representing (candidate) species to their expected (candidate) species, confirming the markers are suitable for species delineation. newhybrids, a hybrid index and hiest confirm the 48 individuals from the presumed hybrid population to be genetically admixed, illustrating the potential of the markers to identify interspecific hybridization. We expect the set of markers we designed to provide a high resolving power for analysis of hybridization in Triturus.

The variability of phenol compounds based on karyological studies of taxa of the genus Vaccinium L., subgenus Oxycoccus (Hill) A. Gray

52 population samples from Poland and several European countries were subjected to karyological and chemotaxonomic studies. Two diploid species (&lt;em&gt;Vaccinium macrocarpon&lt;/em&gt; Ait. and &lt;em&gt;V. microcarpum&lt;/em&gt; (Turcz, ex Rupr.) Schmalh.) with chromosome number 2n = 24 were found, differing essentially in the chemical composition of their phenol fractions. Besides diploid species, a tetraploid V. oxycoccos L., with the chromosome number 2n = 48 was distinguished. It is, characterized by a high chemical variability. Its chromatograms show spots of compounds characteristic of both subspecies distinguished. No hexaploid &lt;em&gt;V. hagerupii&lt;/em&gt; (Löve et Löve) Rothm. with chromosome number 2n = 72 was in the karyologically studied material. Chemical studies of a herbarium sample do not confirm the distinctness of this taxon in relation to &lt;em&gt;V. oxycoccos&lt;/em&gt;. The karyological studies, which, however, need replication, have also revealed the presence of a presumed hybrid, &lt;em&gt;V. pseudonanum&lt;/em&gt; Keller, with chromosome number 2n = 36. The chromatogram of that taxon is very similar to that of V. oxycoccos L. subsp. &lt;em&gt;microphyllus&lt;/em&gt; (Lange) Löve et Löve.

Host Adaptation and Speciation through Hybridization and Polyploidy in Phytophthora

It is becoming increasingly evident that interspecific hybridization is a common event in phytophthora evolution. Yet, the fundamental processes underlying interspecific hybridization and the consequences for its ecological fitness and distribution are not well understood. We studied hybridization events in phytophthora clade 8b. This is a cold-tolerant group of plant pathogenic oomycetes in which six host-specific species have been described that mostly attack winter-grown vegetables. Hybrid characterization was done by sequencing and cloning of two nuclear (ITS and Ypt1) and two mitochondrial loci (Cox1 and Nadh1) combined with DNA content estimation using flow cytometry. Three different mtDNA haplotypes were recovered among the presumed hybrid isolates, dividing the hybrids into three types, with different parental species involved. In the nuclear genes, additivity, i.e. the presence of two alleles coming from different parents, was detected. Hybrid isolates showed large variations in DNA content, which was positively correlated with the additivity in nuclear loci, indicating allopolyploid hybridization followed by a process of diploidization. Moreover, indications of homeologous recombination were found in the hybrids by cloning ITS products. The hybrid isolates have been isolated from a range of hosts that have not been reported previously for clade 8b species, indicating that they have novel pathogenic potential. Next to this, DNA content measurements of the non-hybrid clade 8b species suggest that polyploidy is a common feature of this clade. We hypothesize that interspecific hybridization and polyploidy are two linked phenomena in phytophthora, and that these processes might play an important and ongoing role in the evolution of this genus.