Genome‐specific introgression between wheat and its wild relative Aegilops triuncialis

Introgression of sequences from crop species in wild relatives is of fundamental and practical concern. Here, we address gene flow between cultivated wheat and its widespread polyploid relative, Aegilops triuncialis, using 12 EST‐SSR markers mapped on wheat chromosomes. The presence of wheat diagnostic alleles in natural populations of the barbed goatgrass growing in proximity to cultivated fields highlights that substantial gene flow occurred when both species coexisted. Furthermore, loci from the A subgenome of wheat were significantly less introgressed than sequences from other subgenomes, indicating differential introgression into Ae. triuncialis. Gene flow between such species sharing nonhomeologous chromosomes addresses the evolutionary outcomes of hybridization and may be important for efficient gene containment.     

A cereal cyst nematode (Heterodera avenae Woll.) resistance gene transferred from Aegilops triuncialis to hexaploid wheat

 The cereal cyst nematode (Heterodera avenae) is an important root parasite of common wheat. A high level of resistance was transferred to wheat from Aegilops triuncialis (TR lines) using the cross [(T. turgidum×Ae. triuncialis)×T. aestivum]. Low fertility (3–5 viable kernels per plant) was observed during the process but the surviving hybrid plants were highly vigorous. To obtain stable resistant lines further crosses to T. aestivum were performed. The resistance in TR lines seems to be transferred from the C genome of Ae. triuncialis (genomes CCUU). Ae. triuncialis was highly resistant to the two Spanish populations of H. avenae tested, as well as to four French races and two Swedish populations. The histological analysis showed a hypersensitive reaction in the roots of a resistant TR line inoculated with the Ha71 pathotype of H. avenae, whereas well-formed syncytia were observed in the roots of the susceptible control. Resistance to the H. avenae Ha71 pathotype seemed to be inherited as determined by a single dominant factor in the crosses between resistant TR lines and susceptible cultivars. Received: 11 November 1997 / Accepted: 9 December 1997     

Phenotypic and genetic diversity of leaf rust resistance in wheat wild relatives

Puccinia triticina (Pt), the causal agent of leaf rust evolves through forming new pathotypes that adversely affect the growth and yield of wheat cultivars. Therefore, continued production of resistant varieties through exploring novel sources of resistance in wild relatives which are abundantly found in Iran and the neighbouring regions is a major task in wheat breeding programs. The aim of the present study was to explore 60 wild wheat genotypes selected from the species Triticum monococcum, Aegilops tauschii, Ae. neglecta, Ae. cylindrica, Ae. triuncialis, Ae. umbellulata, Ae. speltoides, Ae. columnaris, Ae. crassa and Ae. ventricosa for resistance to leaf rust. The cultivar ‘Boolani’ and Thatcher near-isogenic lines were used as controls. Two-week-old seedlings were inoculated using 10 Pt pathotypes, and the infection types were recorded. The genotypes were also analysed for polymorphism using six sequence-tagged sites (STS) and sequence characterized amplified region (SCAR) markers. Forty-eight genotypes produced high infection types (3⁺) for two pathotypes, but the remaining genotypes produced low infection types of ‘0; ^=’ to ‘1⁺CN’ to all pathotypes. The latter included three accessions of Ae. tauschii, two accessions of each Ae. umbellulata, Ae. columnaris and Triticum monococcum, and one accession from each Ae. triuncialis, Ae. ventricosa and Ae. neglecta. Analysis for STS and SCAR markers suggested several genotypes could carry the genes Lr9, Lr10, Lr19, Lr24, Lr26 and Lr37 or their potential orthologs in addition to unknown resistance genes. In conclusion, the identified resistant genotypes could be further characterized and used in wheat breeding programs for leaf rust resistance.     

Distribution and characterization of Aegilops and Triticum species from the Bulgarian Black Sea coast

A total of 158 Aegilops-Triticum samples representing six Aegilops species (one diploid, four tetraploid and one hexaploid) and one diploid Triticum were collected along the Bulgarian Black Sea coast, and their distribution on the 350 km long coastal line was reported. The region south of Kamchia river, accepted as the middle point of the coast, was characterized by the greatest diversity of these wild relatives of wheat. The most widely distributed species in this area was Ae. geniculata. Ae. cylindrica was distributed only in north (Durankulak), while Ae. biuncialis and Ae. triuncialis were collected both north and south of Kamchia river. All samples of Ae. neglecta were hexaploid. Natural hybrids of goatgrass and wheat were found in Ae. cylindrica populations. Triticum monococcum ssp. aegilopoides had limited distribution in the south region. Aegilops uniaristata was recorded as a new species for the Bulgarian flora. Most of the samples expressed resistance to powdery mildew in seedling and adult stage, but all of them were polymorphic regarding the resistance to leaf rust (cultures 73760 and 43763). The study revealed additional data for the distribution of Aegilops and Triticum species in Bulgaria and their potential value as genetic resources in wheat improvement.     

Microsatellite polymorphism in natural populations of wild emmer wheat,Triticum dicoccoides,in Israel

Diversity in 20 microsatellite loci of wild emmer wheat, Triticum dicoccoides, was examined in 15 populations (135 genotypes) representing a wide range of ecological conditions of soil, temperature, and water availability, in Israel and Turkey. An extensive amount of diversity at microsatellite loci was observed despite the predominantly selfing nature of this plant species. The 20 Gatersleben wheat microsatellites (GWM), representing 13 chromosomes of genomes A and B of wheat, revealed a total of 364 alleles, with an average of 18 alleles per GWM marker (range: 5–26). The proportion of polymorphic loci per population averaged 0.90 (range: 0.45– 1.00); genic diversity, He, averaged 0.50 (range 0.094– 0.736); and Shannon’s information index averaged 0.84 (range 0.166–1.307). The coefficients of genetic distance between populations were high and averaged D=1.862 (range 0.876–3.320), an indication of sharp genetic divergence over short distances. Interpopulation genetic distances showed no association with geographic distance between the population sites of origin, which ruled out a simple isolation by distance model. Genetic dissimilarity values between genotypes were used to produce a dendrogram of the relationships among wild wheat populations by the unweighted pair-group method with arithmetic averages (UPGMA). The results showed that all the wild emmer wheat populations could be distinguished. Microsatellite analysis was found to be highly effective in distinguishing genotypes of T. dicoccoides, originating from diverse ecogeographical sites in Israel and Turkey, with 88% of the 135 genotypes correctly classified into sites of origin by discriminant analysis. Our present microsatellite results are non-random and in agreement with the previously obtained allozyme and RAPD patterns, although the genetic-diversity values obtained with microsatellites are much higher. Significant correlates of microsatellite markers with various climatic and soil factors suggest that, as in allozymes and RAPDs, natural selection causes adaptive microsatellite ecogeographical differentiation, not only in coding, but most importantly in non-coding genomic regions. Hence, the concept of ”junk DNA” needs to be replaced by at least partly regulatory DNA. The obtained results suggest that microsatellite markers are useful for the estimation of genetic diversity in natural populations of T. dicoccoides and for the tagging of agronomically important traits derived from wild emmer wheat. Received: 27 February 2001 / Accepted: 22 March 2001     

Migration without interbreeding: Evolutionary history of a highly selfing Mediterranean grass inferred from whole genomes

Wild plant populations show extensive genetic subdivision and are far from the ideal of panmixia which permeates population genetic theory. Understanding the spatial and temporal scale of population structure is therefore fundamental for empirical population genetics – and of interest in itself, as it yields insights into the history and biology of a species. In this study we extend the genomic resources for the wild Mediterranean grass Brachypodium distachyon to investigate the scale of population structure and its underlying history at whole-genome resolution. A total of 86 accessions were sampled at local and regional scales in Italy and France, which closes a conspicuous gap in the collection for this model organism. The analysis of 196 accessions, spanning the Mediterranean from Spain to Iraq, suggests that the interplay of high selfing and seed dispersal rates has shaped genetic structure in B. distachyon. At the continental scale, the evolution in B. distachyon is characterized by the independent expansion of three lineages during the Upper Pleistocene. Today, these lineages may occur on the same meadow yet do not interbreed. At the regional scale, dispersal and selfing interact and maintain high genotypic diversity, thus challenging the textbook notion that selfing in finite populations implies reduced diversity. Our study extends the population genomic resources for B. distachyon and suggests that an important use of this wild plant model is to investigate how selfing and dispersal, two processes typically studied separately, interact in colonizing plant species.     

Signatures of de‐domestication in autochthonous pig breeds and of domestication in wild boar populations from MC1R and NR6A1 allele distribution

Autochthonous pig breeds are usually reared in extensive or semi‐extensive production systems that might facilitate contact with wild boars and, thus, reciprocal genetic exchanges. In this study, we analysed variants in the melanocortin 1 receptor (MC1R) gene (which cause different coat colour phenotypes) and in the nuclear receptor subfamily 6 group A member 1 (NR6A1) gene (associated with increased vertebral number) in 712 pigs of 12 local pig breeds raised in Italy (Apulo‐Calabrese, Casertana, Cinta Senese, Mora Romagnola, Nero Siciliano and Sarda) and south‐eastern European countries (Kr?kopolje from Slovenia, Black Slavonian and Turopolje from Croatia, Mangalitsa and Moravka from Serbia and East Balkan Swine from Bulgaria) and compared the data with the genetic variability at these loci investigated in 229 wild boars from populations spread in the same macro‐geographic areas. None of the autochthonous pig breeds or wild boar populations were fixed for one allele at both loci. Domestic and wild‐type alleles at these two genes were present in both domestic and wild populations. Findings of the distribution of MC1R alleles might be useful for tracing back the complex genetic history of autochthonous breeds. Altogether, these results indirectly demonstrate that bidirectional introgression of wild and domestic alleles is derived and affected by the human and naturally driven evolutionary forces that are shaping the Sus scrofa genome: autochthonous breeds are experiencing a sort of ‘de‐domestication’ process, and wild resources are challenged by a ‘domestication’ drift. Both need to be further investigated and managed.     

Patterns of introduction and adaptation during the invasion of Aegilops triuncialis (Poaceae) into Californian serpentine soils

Multiple introductions can play a prominent role in explaining the success of biological invasions. One often cited mechanism is that multiple introductions of invasive species prevent genetic bottlenecks by parallel introductions of several distinct genotypes that, in turn, provide heritable variation necessary for local adaptation. Here, we show that the invasion of Aegilops triuncialis into California, USA, involved multiple introductions that may have facilitated invasion into serpentine habitats. Using microsatellite markers, we compared the polymorphism and genetic structure of populations of Ae. triuncialis invading serpentine soils in California to that of accessions from its native range. In a glasshouse study, we also compared phenotypic variation in phenological and fitness traits between invasive and native populations grown on loam soil and under serpentine edaphic conditions. Molecular analysis of invasive populations revealed that Californian populations cluster into three independent introductions (i.e. invasive lineages). Our glasshouse common garden experiment found that all Californian populations exhibited higher fitness under serpentine conditions. However, the three invasive lineages appear to represent independent pathways of adaptation to serpentine soil. Our results suggest that the rapid invasion of serpentine habitats in California may have been facilitated by the existence of colonizing Eurasian genotypes pre‐adapted to serpentine soils.     

Global genetic diversity of Aedes aegypti

Mosquitoes, especially Aedes aegypti, are becoming important models for studying invasion biology. We characterized genetic variation at 12 microsatellite loci in 79 populations of Ae. aegypti from 30 countries in six continents, and used them to infer historical and modern patterns of invasion. Our results support the two subspecies Ae. aegypti formosus and Ae. aegypti aegypti as genetically distinct units. Ae. aegypti aegypti populations outside Africa are derived from ancestral African populations and are monophyletic. The two subspecies co‐occur in both East Africa (Kenya) and West Africa (Senegal). In rural/forest settings (Rabai District of Kenya), the two subspecies remain genetically distinct, whereas in urban settings, they introgress freely. Populations outside Africa are highly genetically structured likely due to a combination of recent founder effects, discrete discontinuous habitats and low migration rates. Ancestral populations in sub‐Saharan Africa are less genetically structured, as are the populations in Asia. Introduction of Ae. aegypti to the New World coinciding with trans‐Atlantic shipping in the 16th to 18th centuries was followed by its introduction to Asia in the late 19th century from the New World or from now extinct populations in the Mediterranean Basin. Aedes mascarensis is a genetically distinct sister species to Ae. aegypti s.l. This study provides a reference database of genetic diversity that can be used to determine the likely origin of new introductions that occur regularly for this invasive species. The genetic uniqueness of many populations and regions has important implications for attempts to control Ae. aegypti, especially for the methods using genetic modification of populations.     

Experimental and genetic analyses reveal that inbreeding depression declines with increased self‐fertilization among populations of a coastal dune plant

Theory predicts that inbreeding depression (ID) should decline via purging in self‐fertilizing populations. Yet, intraspecific comparisons between selfing and outcrossing populations are few and provide only mixed support for this key evolutionary process. We estimated ID for large‐flowered (LF), predominantly outcrossing vs. small‐flowered (SF), predominantly selfing populations of the dune endemic Camissoniopsis cheiranthifolia by comparing selfed and crossed progeny in glasshouse environments differing in soil moisture, and by comparing allozyme‐based estimates of the proportion of seeds selfed and inbreeding coefficient of mature plants. Based on lifetime measures of dry mass and flower production, ID was stronger in nine LF populations [mean δ = 1?(fitness of selfed seed/fitness of outcrossed seed) = 0.39] than 16 SF populations (mean δ = 0.03). However, predispersal ID during seed maturation was not stronger for LF populations, and ID was not more pronounced under simulated drought, a pervasive stress in sand dune habitat. Genetic estimates of δ were also higher for four LF (δ = 1.23) than five SF (δ = 0.66) populations; however, broad confidence intervals around these estimates overlapped. These results are consistent with purging, but selective interference among loci may be required to maintain strong ID in partially selfing LF populations, and trade‐offs between selfed and outcrossed fitness are likely required to maintain outcrossing in SF populations.     

Hybridization of wheat and Aegilops cylindrica: development,karyomorphology, DNA barcoding and salt tolerance of the amphidiploids

The development of salt‐tolerant genotypes is key to a better utilization of salinized irrigated lands. Given the relatively low genetic diversity within the cultivated wheats for salt tolerance, exploring the Aegilops cylindrica's genetic diversity for salt tolerance is thus crucial to breed wheat for saline environments. In the current study, wheat genotypes were hybridized with Ae. cylindrica (a hyper salt-tolerant genotype), and amphidiploid plants were produced using embryo rescue and chromosome doubling techniques. Crossability and cytological examinations of amphidiploids and BC₁ were performed before sequencing the ITS4/5 and trnE/trnF DNAs to explore the phylogenetic relationships of the amphidiploids and their parents. Finally, amphidiploids were assessed for salt tolerance. Only two common wheat cultivars (‘Chinese Spring’ and ‘Roshan’) were crossable with Ae. cylindrica. The resultant intergeneric hybrids possessed 70 chromosomes, and morphologically either were similar to the male parent in ‘Chinese Spring’ × Ae. cylindrica or tended to be intermediate between parents in ‘Roshan’ × Ae. cylindrica. The phylogenetic tree divided the genotypes into two groups, in which Clade I contained Ae. cylindrica and three amphidiploids, and Clade II consisted of female parents and one amphidiploid. Amphidiploids exhibited significantly higher tolerance to salt stress compared to the female parents (wheat cultivars) in terms of a higher dry matter, lower accumulation of Na, higher K, and higher K/Na ratio in their root and leaf tissues. Taken together, the amphiploid plants might contain valuable salt tolerance factors.

     

Malaysian weedy rice shows its true stripes: wild Oryza and elite rice cultivars shape agricultural weed evolution in Southeast Asia

Weedy rice is a close relative of domesticated rice (Oryza sativa) that competes aggressively with the crop and limits rice productivity worldwide. Most genetic studies of weedy rice have focused on populations in regions where no reproductively compatible wild Oryza species occur (North America, Europe and northern Asia). Here, we examined the population genetics of weedy rice in Malaysia, where wild rice (O. rufipogon) can be found growing in close proximity to cultivated and weedy rice. Using 375 accessions and a combined analysis of 24 neutral SSR loci and two rice domestication genes (sh4, controlling seed shattering, and Bh4, controlling hull colour), we addressed the following questions: (i) What is the relationship of Malaysian weedy rice to domesticated and wild rice, and to weedy rice strains in the USA? (ii) To what extent does the presence of O. rufipogon influence the genetic and phenotypic diversity of Malaysian weeds? (iii) What do the distributions of sh4 and Bh4 alleles and associated phenotypes reveal about the origin and contemporary evolution of Malaysian weedy rice? Our results reveal the following: independent evolutionary origins for Malaysian weeds and US strains, despite their very close phenotypic resemblance; wild‐to‐weed gene flow in Malaysian weed populations, including apparent adaptive introgression of seed‐shattering alleles; and a prominent role for modern Malaysian cultivars in the origin and recent proliferation of Malaysian weeds. These findings suggest that the genetic complexity and adaptability of weedy crop relatives can be profoundly influenced by proximity to reproductively compatible wild and domesticated populations.     

Major structural genomic alterations can be associated with hybrid speciation in Aegilops markgrafii (Triticeae)

During evolutionary history many grasses from the tribe Triticeae have undergone interspecific hybridization, resulting in allopolyploidy; whereas homoploid hybrid speciation was found only in rye. Homoeologous chromosomes within the Triticeae preserved cross‐species macrocolinearity, except for a few species with rearranged genomes. Aegilops markgrafii, a diploid wild relative of wheat (2n = 2x = 14), has a highly asymmetrical karyotype that is indicative of chromosome rearrangements. Molecular cytogenetics and next‐generation sequencing were used to explore the genome organization. Fluorescence in situ hybridization with a set of wheat cDNAs allowed the macrostructure and cross‐genome homoeology of the Ae. markgrafii chromosomes to be established. Two chromosomes maintained colinearity, whereas the remaining were highly rearranged as a result of inversions and inter‐ and intrachromosomal translocations. We used sets of barley and wheat orthologous gene sequences to compare discrete parts of the Ae. markgrafii genome involved in the rearrangements. Analysis of sequence identity profiles and phylogenic relationships grouped chromosome blocks into two distinct clusters. Chromosome painting revealed the distribution of transposable elements and differentiated chromosome blocks into two groups consistent with the sequence analyses. These data suggest that introgressive hybridization accompanied by gross chromosome rearrangements might have had an impact on karyotype evolution and homoploid speciation in Ae. markgrafii.     

Unreduced gamete formation in wheat × <Emphasis Type="Italic">Aegilops</Emphasis> spp. hybrids is genotype specific and prevented by shared homologous subgenomes

Key message

The presence of homologous subgenomes inhibited unreduced gamete formation in wheat × Aegilops interspecific hybrids. Unreduced gamete rates were under the control of the wheat nuclear genome.

Abstract

Production of unreduced gametes is common among interspecific hybrids, and may be affected by parental genotypes and genomic similarity. In the present study, five cultivars of Triticum aestivum and two tetraploid Aegilops species (i.e. Ae. triuncialis and Ae. cylindrica) were reciprocally crossed to produce 20 interspecific hybrid combinations. These hybrids comprised two different types: T. aestivum × Aegilops triuncialis; 2n = ABDU^tC^t (which lack a common subgenome) and T. aestivum × Ae. cylindrica; 2n = ABDD^cC^c (which share a common subgenome). The frequency of unreduced gametes in F₁ hybrids was estimated in sporads from the frequency of dyads, and the frequency of viable pollen, germinated pollen and seed set were recorded. Different meiotic abnormalities recorded in the hybrids included precocious chromosome migration to the poles at metaphase I and II, laggards in anaphase I and II, micronuclei and chromosome stickiness, failure in cell wall formation, premature cytokinesis and microspore fusion. The mean frequency of restitution meiosis was 10.1 %, and the mean frequency of unreduced viable pollen was 4.84 % in T. aestivum × Ae. triuncialis hybrids. By contrast, in T. aestivum × Ae. cylindrica hybrids no meiotic restitution was observed, and a low rate of viable gametes (0.3 %) was recorded. This study present evidence that high levels of homologous pairing between the D and D^c subgenomes may interfere with meiotic restitution and the formation of unreduced gametes. Variation in unreduced gamete production was also observed between T. aestivum × Ae. triuncialis hybrid plants, suggesting genetic control of this trait.

     

AB-QTL analysis in winter wheat: I. Synthetic hexaploid wheat (<Emphasis Type="Italic">T. turgidum</Emphasis> ssp. <Emphasis Type="Italic">dicoccoides </Emphasis> × <Emphasis Type="Italic">T. tauschii</Emphasis>) as a source of favourable alleles for milling and baking quality traits

The advanced backcross QTL (AB-QTL) strategy was utilised to locate quantitative trait loci (QTLs) for baking quality traits in two BC₂F₃ populations of winter wheat. The backcrosses are derived from two German winter wheat cultivars, Batis and Zentos, and two synthetic, hexaploid wheat accessions, Syn022 and Syn086. The synthetics originate from hybridisations of wild emmer (T. turgidum spp. dicoccoides) and T. tauschii, rather than from durum wheat and T. tauschii and thus allowed for the first time to test for exotic QTL effects on wheat genomes A and B in addition to genome D. The investigated quality traits comprised hectolitre weight, grain hardness, flour yield Type 550, falling number, grain protein content, sedimentation volume and baking volume. One hundred and forty-nine SSR markers were applied to genotype a total of 400 BC₂F₃ lines. For QTL detection, a mixed-model ANOVA was conducted, including the effects DNA marker, BC₂F₃ line, environment and marker × environment interaction. Overall 38 QTLs significant for a marker main effect were detected. The exotic allele improved trait performance at 14 QTLs (36.8%), while the elite genotype contributed the favourable effect at 24 QTLs (63.2%). The favourable exotic alleles were mainly associated with grain protein content, though the greatest improvement of trait performance due to the exotic alleles was achieved for the traits falling number and sedimentation volume. At the QTL on chromosome 4B the exotic allele increased the falling number by 19.6% and at the QTL on chromosome 6D the exotic allele led to an increase of the sedimentation volume by 21.7%. The results indicate that synthetic wheat derived from wild emmer × T. tauschii carries favourable QTL alleles for baking quality traits, which might be useful for breeding improved wheat varieties by marker-assisted selection.     

New cytoplasmic male sterility sources in common wheat: Their genetical and breeding considerations

Summary Nuclei from Triticum aestivum L. cultivars Penjamo 62 and Siete Cerros 66 were introduced into the cytoplasms of different species of Aegilops and some subspecies (varieties) of T. dicoccoides by backcrossing. The sterile alloplasmic lines obtained were compared with the normal cultivars used as the recurrent pollen parents. According to the cytoplasmic effect, these cytoplasms were subdivided into three main groups. The first group possesses C^u type cytoplasm, the second one possesses M type and the third group includes S, C and G type. Promising male sterile cytoplasms for hybrid wheat production were found in Ae. mutica, Ae. triuncialis and T. dicoccoides var. spontaneovillosum. Based on these results and other information some conjectures were made concerning hybrid wheat breeding and phylogenetic differentiations of the cytoplasm.     

Variation in Aggressiveness Components in the Hemileia vastatrix Population in Brazil

The Pucciniomycete fungus Hemileia vastatrix causes leaf rust on coffee trees. The pathogen is responsible for considerable yield losses in susceptible coffee cultivars if appropriate management strategies are not implemented. Rapid spread and epidemics of rust fungi are usually associated with the emergence of new races of the pathogen that overcome resistance or with the emergence of more aggressive populations of the pathogen. In Brazil, coffee production is dominated by susceptible cultivars of Coffea arabica and Coffea canephora. We assessed aggressiveness in 46 populations of H. vastatrix from Minas Gerais and Espírito Santo, two of the most important coffee‐producing states in Brazil. We observed a significant difference in the incubation period between the populations from Minas Gerais and Espírito Santo when 183 single‐pustule isolates were inoculated onto Catuaí Vermelho IAC 44, a susceptible C. arabica cultivar. Variation in aggressiveness components was observed between and within localities. Isolates with longer incubation periods also tended to have longer latent periods, although there was only a low correlation between these two aggressiveness components (r² = 0.34, P = 2.2 × 10^?16). Low‐sporulating isolates also had significantly longer incubation and latent periods. The H. vastatrix population from Minas Gerais and Espírito Santo is structured by the formation of groups of individuals with differential level of aggressiveness. Our results indicate that the variation in aggressiveness of the Brazilian H. vastatrix population may be associated with the geographic coffee‐producing areas.     

Cytoplasmic male sterility in the olive (Olea europaea L.)

The olive tree is usually hermaphrodite but self-incompatible. In the Western Mediterranean some cultivars are totally male-sterile. Three different male-sterile phenotypes have been recognised. To infer the genetic basis of male sterility we studied its inheritance and cytoplasmic diversity in wild (oleaster) and cultivated Mediterranean olive. In the cross Olivière×Arbequina, the male-sterile trait was maternally inherited and affected all progenies. We also checked that both chloroplast and mitochondrial DNAs are maternally inherited. RFLP studies on chloroplast and mitochondrial DNAs revealed several cytotypes: two chlorotypes and four mitotypes in cultivars and oleaster (wild or feral Mediterranean olive). Furthermore, a total linkage desequilibrium between the CCK chlorotype and the MCK mitotype in cultivars and oleaster from different regions supports the fact that paternal leakage of organelles was not observed. The male sterility (ms 2) displayed by Olivière, plus six other cultivars and three oleaster was strictly associated with the CCK chlorotype and the MCK mitotype. These facts suggest that Olivière carries cytoplasmic male sterility. Male-fertile and male-sterile oleasters carrying this cytotype showed the presence of restorer alleles. This CMS might be due to a distant cross between olive taxa. The two other male-sterile phenotypes displayed by Lucques (ms 1) and Tanche (ms 3) were associated with the ME1 mitotype but we have not demonstrated CMS. Received: 26 July 1999 / Accepted: 27 August 1999     

A Bayesian analysis of gene flow from crops to their wild relatives: cultivated (Lactuca sativa L.) and prickly lettuce (L. serriola L.) and the recent expansion of L. serriola in Europe

Interspecific gene flow can lead to the formation of hybrid populations that have a competitive advantage over the parental populations, even for hybrids from a cross between crops and wild relatives. Wild prickly lettuce (Lactuca serriola) has recently expanded in Europe and hybridization with the related crop species (cultivated lettuce, L. sativa) has been hypothesized as one of the mechanisms behind this expansion. In a basically selfing species, such as lettuce, assessing hybridization in natural populations may not be straightforward. Therefore, we analysed a uniquely large data set of plants genotyped with SSR (simple sequence repeat) markers with two programs for Bayesian population genetic analysis, STRUCTURE and NewHybrids. The data set comprised 7738 plants, including a complete genebank collection, which provided a wide coverage of cultivated germplasm and a fair coverage of wild accessions, and a set of wild populations recently sampled across Europe. STRUCTURE analysis inferred the occurrence of hybrids at a level of 7% across Europe. NewHybrids indicated these hybrids to be advanced selfed generations of a hybridization event or of one backcross after such an event, which is according to expectations for a basically selfing species. These advanced selfed generations could not be detected effectively with crop‐specific alleles. In the northern part of Europe, where the expansion of L. serriola took place, the fewest putative hybrids were found. Therefore, we conclude that other mechanisms than crop/wild gene flow, such as an increase in disturbed habitats and/or climate warming, are more likely explanations for this expansion.     

Wolbachia pipientis occurs in Aedes aegypti populations in New Mexico and Florida,USA

The mosquitoes Aedes aegypti (L.) and Ae. albopictus Skuse are the major vectors of dengue, Zika, yellow fever, and chikungunya viruses worldwide. Wolbachia, an endosymbiotic bacterium present in many insects, is being utilized in novel vector control strategies to manipulate mosquito life history and vector competence to curb virus transmission. Earlier studies have found that Wolbachia is commonly detected in Ae. albopictus but rarely detected in Ae. aegypti. In this study, we used a two‐step PCR assay to detect Wolbachia in wild‐collected samples of Ae. aegypti. The PCR products were sequenced to validate amplicons and identify Wolbachia strains. A loop‐mediated isothermal amplification (LAMP) assay was developed and used for detecting Wolbachia in selected mosquito specimens as well. We found Wolbachia in 85/148 (57.4%) wild Ae. aegypti specimens from various cities in New Mexico, and in 2/46 (4.3%) from St. Augustine, Florida. Wolbachia was not detected in 94 samples of Ae. aegypti from Deer Park, Harris County, Texas. Wolbachia detected in Ae. aegypti from both New Mexico and Florida was the wAlbB strain of Wolbachia pipientis. A Wolbachia‐positive colony of Ae. aegypti was established from pupae collected in Las Cruces, New Mexico, in 2018. The infected females of this strain transmitted Wolbachia to their progeny when crossed with males of Rockefeller strain of Ae. aegypti, which does not carry Wolbachia. In contrast, none of the progeny of Las Cruces males mated to Rockefeller females were infected with Wolbachia.