中国蜜环菌生物种与北美种的交配关系

将中国三个未知蜜环菌生物种A、C、D的38个代表菌株与北美蜜环菌A．sinopina、A．calvescens、A．nabsnona、A．gemina、A．ostoyae、NABSX等六个种的22个代表菌株进行了配对试验,结果表明中国生物种A与北美种A．sinopina互交可育,属于同一种。中国生物种C与任一北美种都互交不育,不存在部分可育现象,为亚洲特有种。中国生物种D与欧美的A．ostoyae的两个菌株互交可育,实验证实该种另外四个欧美菌株已经失去交配能力,因此确认中国生物种D与A．ostoyae属于同种。     

大兴安岭和长白山地区蜜环菌生物种的研究

从大兴安岭和长白山采集到30号蜜环菌(Armillaria mellea)标本,选其中有代表性的10个号的担子果获得单孢株。交配试验表明每一担子果都具有双因子异宗配合系。不同子实体交配型之间交配结果表明,在大兴安岭和长白山地区蜜环菌目前至少存在5个生物种,分别称为生物种A、B、C、D和E。将这5个生物种的单孢菌种与欧洲5个蜜环菌生物种的单孢菌株进行配合,生物种B与欧洲A.gallica,生物种E与欧洲A.ostoyae亲和交配,因此将生物种B和E分别定为A.gallica和A.ostoyae。生物种A、C和D则不与任何欧洲生物种交配。     

Mycelial interactions inSclerotinia sclerotiorum

Mycelial interactions were examined among 35 isolates ofSclerotinia sclerotiorum and two Asian species,Sclerotinia asari and an unnamed, Japanese species. Pairings were scored as compatible when strains merged to form one colony and incompatible when strains grew to form two distinct colonies. Incompatible mycelial pairings resulted in an interaction zone in which a distinct reaction line and abundant aerial mycelium or thin mycelium were observed with some variation among replicates. All pairings of a strain with itself were compatible. Of the 31 strains ofS. sclerotiorum tested, 21 were mycelially incompatible with all others. Among the remaining 10 strains ofS. sclerotiorum, there were four mycelial compatibility groups consisting of two or three strains each. Pairings ofS. asari with all other strains resulted in a unique incompatible reaction, a mycelium-free interaction zone. Two of three strains of the Japanese species were intercompatible, but pairings of each of the three strains with all other strains were incompatible. Microscopically, mycelial interactions in pairings of strains were complex. Anastomosis between paired strains was not always observed. This may be due in part to the conversion of many hyphal tips, in both compatible and incompatible interactions, to sites of microconidiogenesis no longer capable of hyphal fusion. Incompatible pairings were followed by hyphal deterioration in one or both strains; hyphal deterioration was not observed in compatible interactions. Of the 31 strains tested, 4 strains ofS. sclerotiorum produced apothecia. Pairings between single ascospore isolates within each strain were compatible, as were pairings with the parent isolate. Mycelial interactions of single ascospore isolates with other strains were identical to those of the parent isolate, indicating that the parent fruitbody was homozygous for any determinant(s) of mycelial incompatibility. The data from this study suggest that a high level of mycelial incompatibility exists among strains ofS. sclerotiorum, comparable to levels of vegetative incompatibility reported in other ascomycetes, that the extent of mycelial incompatibility indicates that genetic heterogeneity exists within the species, and that mycelial compatibility/incompatibility reactions may be an effective way of categorizing intraspecific heterogeneity.     

中国蜜环菌的新生物种

在调查研究蜜环菌生物种的过程中,先后在东北、华北、华中和西南地区,发现了四个新的中国蜜环菌生物种,CBS F、CBS G、CBS H和CBS I。研究表明,CBS G属于典型的同宗配合种,其余三个为异宗配合。CBS H与CBS C之间存在部分互交可育,比例高达17.8%,在同一个国家的两个种之间出现如此高的互交可育比例还是首次报道。上述三个生物种同欧美的已知蜜环菌种均互交不育,为亚洲特有种。CBS I为无菌环的假蜜环菌A.tabescens (Scop. ) Emel,它与欧洲的假蜜环菌互交可育,属于同种。但同中国其它各生物种互交不育。同时讨论了蜜环菌生物种的群体观点。     

Intraspecific sterility barrier confirms that introduction of Sphaerotrichia divaricata (Phaeophyceae,Chordariales) into the Mediterranean was from Japan

Crossing studies revealed an intraspecific sterility barrier on the level of zygote formation between Japanese Sphaerotrichia divaricata and isolates of the same species from the Northeast Pacific and the North Atlantic. Because no consistent morphological differences exist between sporophytes from Japan and other areas, we propose not to distinguish the intersterile populations as different species. Japanese Sphaerotrichia and isolates from a recently detected population in the Étang de Thau, French Mediterranean coast, are interfertile. The crossing studies support the assumption that this Mediterranean population is a recent introduction from Japan.     

Genetic and morphological comparisons ofGlomerella (Colletotrichum) isolates from maize and from sorghum

Various morphological and genetic characteristics were compared among six isolates ofColletotrichum from maize and six from sorghum. For the first time, a teleomorph was induced in sorghum isolates by pairing them on autoclaved sorghum leaves in a humidity chamber. The sorghum teleomorph was morphologically similar toGlomerella graminicola andGlomerella tucumanensis, the teleomorphs ofColletotrichum isolates from maize and from sugarcane, respectively. Mating tests demonstrated thatGlomerella isolates from maize and sorghum were not interfertile. Several small but consistent differences in the morphologies of the isolates from maize and from sorghum were observed which agreed with earlier reports. DNA fingerprints detected as restriction fragment length polymorphisms of mitochondrial DNA and random polymorphic DNA (RAPD) produced from nuclear DNA by the polymerase chain reaction could be used to reliably and unambiguously distinguish members of the two groups of isolates. Results of a statistical analysis of similarity of the RAPD fingerprints suggested that maize and sorghum isolates ofColletotrichum are only about 45% similar (±10%) and represent two distinct and separate genetic lineages. We conclude that isolates ofColletotrichum from maize and sorghum are sibling species since they are morphologically very similar but reproductively completely isolated.     

Evidence for amphithallism and broad geographical hybridization potential among Agaricus subrufescens isolates from Brazil,France, and Thailand

Agaricus subrufescens is a cultivated edible and medicinal mushroom. Its known geographical distribution encompasses the Americas, Europe, Oceania, and Asia. The objective of this study was to assess mating compatibility and interfertility of strains originating from Brazil, France, and Thailand. Progeny of each strain were analyed with codominant molecular markers. Multilocus genotype tests revealed that the three strains were amphithallic with percentages of heterokaryotic single spore progenies of 75 % for the Thai strain and around 40 % for the Brazilian and French strains. In mating tests A. subrufescens had a multiallelic unifactorial system of sexual incompatibility. The three parent strains were interfertile based on experimental pairings of single-spore isolates, the recovery of hybrid heterokaryons from compatible matings, and the ability of hybrids to produce mushrooms and fertile spores. This biological approach supports the inclusion of the European strains within the species and the extension of the geographical distribution range to Asia. Our data should help to develop breeding strategies and to better manage and exploit the diversity existing in A. subrufescens.     

Phylogeny and taxonomy of the North American clade of the Ceratocystis fimbriata complex

Ceratocystis fimbriata is a widely distributed, plant pathogenic fungus that causes wilts and cankers on many woody hosts. Earlier phylogenetic analyses of DNA sequences revealed three geographic clades within the C. fimbriata complex that are centered respectively in North America, Latin America and Asia. This study looked for cryptic species within the North American clade. The internal transcribed spacer regions (ITS) of the rDNA were sequenced, and phylogenetic analysis indicated that most isolates from the North American clade group into four host-associated lineages, referred to as the aspen, hickory, oak and cherry lineages, which were isolated primarily from wounds or diseased trees of Populus, Carya, Quercus and Prunus, respectively. A single isolate collected from P. serotina in Wisconsin had a unique ITS sequence. Allozyme electromorphs also were highly polymorphic within the North American clade, and the inferred phylogenies from these data were congruent with the ITS-rDNA analyses. In pairing experiments isolates from the aspen, hickory, oak and cherry lineages were interfertile only with other isolates from their respective lineages. Inoculation experiments with isolates of the four host-associated groupings showed strong host specialization by isolates from the aspen and hickory lineages on Populus tremuloides and Carya illinoensis, respectively, but isolates from the oak and cherry lineages did not consistently reveal host specialization. Morphological features distinguish isolates in the North American clade from those of the Latin American clade (including C. fimbriata sensu stricto). Based on the phylogenetic evidence, interfertility, host specialization and morphology, the oak and cherry lineages are recognized as the earlier described C. variospora, the poplar lineage as C. populicola sp. nov., and the hickory lineage as C. caryae sp. nov. A new species associated with the bark beetle Scolytus quadrispinosus on Carya is closely related to C. caryae and is described as C. smalleyi.     

The root rot fungus Armillaria mellea introduced into South Africa by early Dutch settlers

Dead and dying oak (Quercus) and numerous other woody ornamental trees and shrubs showing signs and symptoms of Armillaria root rot were identified in the Company Gardens, Cape Town, South Africa, which were established in the mid-1600s by the Dutch East Indies Trading Company. Nineteen isolates from dying trees or from mushrooms were collected and analysed to identify and characterize the Armillaria sp. responsible for the disease. The AluI digestion of the amplified product of the first intergenic spacer region (IGS-1) of the rRNA operon of 19 isolates from the Company Gardens was identical to that of some of the European isolates of A. mellea s. s. The IGS-1 region and the internal transcribed spacers (ITS) were sequenced for some of the Cape Town isolates. Phylogenetic analyses placed the Cape Town isolates in the European clade of A. mellea, which is distinct from the Asian and North American clades of this species. Identification based on sexual compatibility was conducted using A. mellea tester strains in diploid-haploid pairings, which showed some compatibility between the Cape Town isolates and testers from Europe. Somatic compatibility tests (diploid-diploid pairings) and DNA fingerprinting with multilocus, microsatellite probes indicated that the Cape Town isolates were genetically identical and may have resulted from vegetative (clonal) spread from a single focus in the centre of the original Company Gardens (c. 1652). The colonized area is at least 345 m in diameter. Assuming a linear spread rate underground of 0.3 m/year to 1.6 m/year, the genet (clone) was estimated to be between 108 and 575 years old. These data suggest that A. mellea was introduced into Cape Town from Europe, perhaps on potted plants, such as grapes or citrus, planted in the Company Gardens more than 300 years ago.     

Identification of Gremmeniella abietina Races with Random Amplified Polymorphic DNA Markers

Seven random amplified polymorphic DNA (RAPD) markers amplified from four oligonucleotides (10-mers) by the polymerase chain reaction were used to distinguish between the North American and European races of Gremmeniella abietina, the causal agent of Scleroderris canker of conifers. Forty-three isolates of the pathogen from 11 different host species originating from 11 countries, states, and provinces were tested; race designation was consistent with results from immunogenic and soluble-protein assays. By using RAPD markers, it was possible to identify G. abietina races by DNA amplifications directly from fruiting bodies, thus eliminating the need to culture the fungus, as is necessary with immunogenic and soluble-protein assays. Two isolates which had been previously classified as intermediate were clearly identified as belonging to either one of the two races by using RAPD markers. No interracial hybrids were detected in our survey. Patterns of amplification products from the European race in North America were identical to patterns of European isolates, further substantiating that this is an introduced race to the North American continent.     

Speciation and demographic history of Atlantic eels (Anguilla anguilla and A. rostrata) revealed by mitogenome sequencing

Processes leading to speciation in oceanic environments without obvious physical barriers remain poorly known. European and American eel (Anguilla anguilla and A. rostrata) spawn in partial sympatry in the Sargasso Sea. Larvae are advected by the Gulf Stream and other currents towards the European/North African and North American coasts, respectively. We analyzed 104 mitogenomes from the two species along with mitogenomes of other Anguilla and outgroup species. We estimated divergence time between the two species to identify major events involved in speciation. We also considered two previously stated hypotheses: one where the ancestral species was present in only one continent but was advected across the Atlantic by ocean current changes and another where population declines during Pleistocene glaciations led to increasing vicariance, facilitating speciation. Divergence time was estimated to ∼3.38 Mya, coinciding with the closure of the Panama Gateway that led to reinforcement of the Gulf Stream. This could have advected larvae towards European/North African coasts, in which case American eel would be expected to be the ancestral species. This scenario could, however, not be unequivocally confirmed by analyses of dN/dS, nucleotide diversity and effective population size estimates. Extended bayesian skyline plots showed fluctuations of effective population sizes and declines during glaciations, and thus also lending support to the importance of vicariance during speciation. There was evidence for positive selection at the ATP6 and possibly ND5 genes, indicating a role in speciation. The findings suggest an important role of ocean current changes in speciation of marine organisms.     

A new species of Epichloë symbiotic with Chinese grasses

Epichlo? species are fungal symbionts (endophytes) of grasses, six European and four North American biological species in genus Epichlo? have been described in previous researches. In this study we describe a new Epichlo? species, Epichlo? yangzii Li et Wang, found in natural symbioses with Roegneria kamoji native to China. We investigated the host specificity, morphology, interfertility tests and molecular phylogenetic evidences of this new species. The results indicated that E. yangzii is host specific and seedborne. Most morphological characteristics of this new species are typical in the genus. However differences are evident in several features including size of perithecia, asci and ascospores. In mating tests E. yangzii was not interfertile with E. elymi isolates from related hosts in genera Elymus. Phylogenetic relationships based on sequences of beta-tubulin gene (tub2) introns and translation elongation factor 1-alpha gene (tef1) introns showed that members of the new species grouped into exclusive clades with high bootstrap value.     

Extended phylogeny of Aquilegia: the biogeographical and ecological patterns of two simultaneous but contrasting radiations

Studies of the North American columbines (Aquilegia, Ranunculaceae) have supported the view that adaptive radiations in animal-pollinated plants proceed through pollinator specialisation and floral differentiation. However, although the diversity of pollinators and floral morphology is much lower in Europe and Asia than in North America, the number of columbine species is similar in the three continents. This supports the hypothesis that habitat and pollinator specialisation have contributed differently to the radiation of columbines in different continents. To establish the basic background to test this hypothesis, we expanded the molecular phylogeny of the genus to include a representative set of species from each continent. Our results suggest that the diversity of the genus is the result of two independent events of radiation, one involving Asiatic and North American species and the other involving Asiatic and European species. The ancestors of both lineages probably occupied the mountains of south-central Siberia. North American and European columbines are monophyletic within their respective lineages. The genus originated between 6.18 and 6.57 million years (Myr) ago, with the main pulses of diversification starting around 3 Myr ago both in Europe (1.25–3.96 Myr ago) and North America (1.42–5.01 Myr ago). The type of habitat occupied shifted more often in the Euroasiatic lineage, while pollination vectors shifted more often in the Asiatic-North American lineage. Moreover, while allopatric speciation predominated in the European lineage, sympatric speciation acted in the North American one. In conclusion, the radiation of columbines in Europe and North America involved similar rates of diversification and took place simultaneously and independently. However, the ecological drivers of radiation were different: geographic isolation and shifts in habitat use were more important in Europe while reproductive isolation linked to shifts in pollinator specialisation additionally acted in North America.     

Transatlantic disjunction in fleshy fungi. I. The Sparassis crispa complex

Phylogenies based on ITS and LSU sequences show that the Sparassis crispa complex comprises several monophyletic clades, in some cases co\rresponding to named taxa (i.e. S. crispa, S. radicata), but others lacking names (i.e. eastern and southwestern North American S. “crispa”). In our study, morphological examination of numerous collections also distinguished subtle differences correlated with geographic distribution. Underlying these problems, several taxa lacked type specimens for taxonomic analysis. In this paper, appropriate epitypes are designated and names assigned. Extensive sexual compatibility experiments, described within, indicate that monokaryon, haploid isolates of collections from North America and Europe are consistently sexually compatible to some degree. Inherent in the study, different “species concepts” were tested, with the “biological species concept,” based on sexual compatibility, being the least restrictive. We propose two new taxa, S. americana and S. americana f. arizonica.     

Novel microsatellite loci reveal high genetic diversity yet low population structure for alfalfa leafcutting bees in North America

The alfalfa leafcutting bee, Megachile rotundata (ALCB) is an economically important pollinator necessary for seed production of the critical forage crop alfalfa, Medicago sativa. The pollinator was accidentally introduced to North America from Europe approximately 70 years ago, and it is primarily produced in Canada and shipped to the United States annually en masse for seed field pollination. We investigate how the large-scale commercial movement of this bee affects the genetic structure of populations in the North American seed growing system and compare the genetic diversity and structure of introduced North American bees with two native European populations. Using 16 newly developed microsatellite loci, we describe the North American population structure of this bee. ALCBs collected from alfalfa seed farms have a degree of genetic variability similar to one native European population, but lower than the second. Considering that the species was accidentally introduced into North America, we anticipated more signature of a founder effect. Despite the level of genetic variability, we found little, if any, genetic structuring across North America, other than that the North American populations were distinct from the European populations sampled. While we detected some sub-structure in North American populations using Bayesian methods, the structuring was without geographic pattern, and we propose it is the result of the intense human management and movement of these bees. The trade and movement of these bees by humans has created a nearly panmictic M. rotundata population across the continent, which has implications relevant to the preservation and conservation of other bee pollinators.     

Susceptibility of North-American and European crickets to Acheta domesticus densovirus (AdDNV) and associated epizootics

The European house cricket, Acheta domesticus L., is highly susceptible to A. domesticus densovirus (AdDNV). Commercial rearings of crickets in Europe are frequently decimated by this pathogen. Mortality was predominant in the last larval stage and young adults. Infected A. domesticus were smaller, less active, did not jump as high, and the adult females seldom lived more than 10-14 days. The most obvious pathological change was the completely empty digestive caecae. Infected tissues included adipose tissue, midgut, epidermis, and Malpighian tubules. Sudden AdDNV epizootics have decimated commercial mass rearings in widely separated parts of North America since the autumn of 2009. Facilities that are producing disease-free crickets have avoided the importation of crickets and other non-cricket species (or nonliving material). Five isolates from different areas in North America contained identical sequences as did AdDNV present in non-cricket species collected from these facilities. The North American AdDNVs differed slightly from sequences of European AdDNV isolates obtained in 1977, 2004, 2006, 2007 and 2009 and an American isolate from 1988. The substitution rate of the 1977 AdDNV 5 kb genome was about two nucleotides per year, about half of the substitutions being synonymous. The American and European AdDNV strains are estimated to have diverged in 2006. The lepidopterans Spodoptera littoralis and Galleria mellonella could not be infected with AdDNV. The Jamaican cricket, Gryllus assimilis, and the European field cricket, Gryllus bimaculatus, were also found to be resistant to AdDNV.     

An analysis of interspecific hybrids and phylogenetic implications inCucumis (Cucurbitaceae)

Investigations on interspecific crossability in 8Cucumis species (2n = 24) and chromosome pairing and pollen fertility of their hybrids from 15 combinations have been utilized for tracing the phylogenetic relationships among these taxa and factors responsible for their differentiation. A collective evaluation of data suggests that there are three broad groups of species, one of the spiny fruited interfertile species, whose hybrids show varying degree of chromosome associations and low to high pollen fertility; the second of species with non-spiny fruits, which are completely incompatible with the former but weakly compatible with the cultivated species,C. melo L. to produce partly developed seeds, and the third group ofC. metuliferus E. Mey. exSchrad. andC. melo and its different botanical varieties. The species with spiny fruits can be further divided based on karyomorphological similarities and/or on relative genomic affinity, indicated by chromosome pairing and hybrid pollen fertility.Cytogenetics inCucumis III.     

Intersterility, morphology and taxonomy of Ceratocystis fimbriata on sweet potato, cacao and sycamore

Ceratocystis fimbriata is a large, diverse complex of species that cause wilt-type diseases of many economically important plants. Previous studies have shown that isolates in three monophyletic lineages within the Latin American clade of C. fimbriata are host-specialized to cacao (Theobroma cacao), sweet potato (Ipomoea batatas) and sycamore (Platanus spp.), respectively. We paired testers of opposite mating type from isolates of these lineages to find intersterility groups. Two intersterility groups corresponded to the sweet potato and sycamore lineages, respectively. The cacao lineage contained two intersterility groups, corresponding to two genetic sublineages centered in western Ecuador and Brazil/Costa Rica/Colombia. Six isolates from cacao that were not members of the cacao lineage and were not pathogenic to cacao in an earlier study also were intersterile with members of the two cacao intersterility groups. Some pairings between testers from different lineages or sublineages yielded perithecia from which a few abnormal progeny could be recovered, typical of interspecific hybrids. These progeny showed abnormal segregation of the MAT-2 gene and mycelial morphology, showing that they were indeed the result of crosses. Isolates of the sweet potato, cacao, and sycamore lineages were indistinguishable morphologically except for the presence or absence of a doliform (barrel-shaped) conidial state and minor differences in size of perithecial bases and necks and ascospores. C. fimbriata originally was described from sweet potato. We describe the cacao pathogen as a new species, Ceratocystis cacaofunesta and we raise the sycamore pathogen from a form to species Ceratocystis platani.     

Genetic Diversity of Isolates of Glomus mosseae from Different Geographic Areas Detected by Vegetative Compatibility Testing and Biochemical and Molecular Analysis

We detected, for the first time, the occurrence of vegetative incompatibility between different isolates of the arbuscular mycorrhizal fungal species Glomus mosseae. Vegetative compatibility tests performed on germlings belonging to the same isolate showed that six geographically different isolates were capable of self-anastomosing, and that the percentage of hyphal contacts leading to fusions ranged from 60 to 85%. Successful anastomoses were characterized by complete fusion of hyphal walls, protoplasm continuity and occurrence of nuclei in the middle of hyphal bridges. No anastomoses could be detected between hyphae belonging to different isolates, which intersected without any reaction in 49 to 68% of contacts. Microscopic examinations detected hyphal incompatibility responses in diverse pairings, consisting of protoplasm retraction from the tips and septum formation in the approaching hyphae, even before physical contact with neighboring hyphae. Interestingly, many hyphal tips showed precontact tropism, suggesting that specific recognition signals may be involved during this stage. The intraspecific genetic diversity of G. mosseae revealed by vegetative compatibility tests was confirmed by total protein profiles and internal transcribed spacer-restriction fragment length polymorphism profiles, which evidenced a higher level of molecular diversity between the two European isolates IMA1 and BEG25 than between IMA1 and the two American isolates. Since arbuscular mycorrhizal fungi lack a tractable genetic system, vegetative compatibility tests may represent an easy assay for the detection of genetically different mycelia and an additional powerful tool for investigating the population structure and genetics of these obligate symbionts.