Population genetics of the potentially invasive African fruit fly species, Ceratitis rosa and Ceratitis fasciventris (Diptera: Tephritidae)

A set of 10 microsatellite markers was used to survey the levels of genetic variability and to analyse the genetic aspects of the population dynamics of two potentially invasive pest fruit fly species, Ceratitis rosa and C. fasciventris, in Africa. The loci were derived from the closely related species, C. capitata. The degree of microsatellite polymorphism in C. rosa and C. fasciventris was extensive and comparable to that of C. capitata. In C. rosa, the evolution of microsatellite polymorphism in its distribution area reflects the colonization history of this species. The mainland populations are more polymorphic than the island populations. Low levels of differentiation were found within the Africa mainland area, while greater levels of differentiation affect the islands. Ceratitis fasciventris is a central-east African species. The microsatellite data over the Uganda/Kenya spatial scale suggest a recent expansion and possibly continuing gene flow within this area. The microsatellite variability data from C. rosa and C. fasciventris, together with those of C. capitata, support the hypothesis of an east African origin of the Ceratitis spp.     

Pathogenicity of Metarhizium anisopliae (Metsch.) Sorokin and Beauveria bassiana (Balsamo) Vuillemin,to three adult fruit fly species: Ceratitis capitata (Weidemann), C. rosa var. fasciventris Karsch and C. cosyra (Walker) (Diptera :Tephritidae)

The pathogenicity of two isolates of Beauveria bassiana and 12 of Metarhizium anisopliae towards adult fruit flies, Ceratitis capitata and Ceratitis rosa var. fasciventris was tested in the laboratory. Fruit flies were exposed to dry conidia evenly spread on velvet material covering the inner side of a cylindrical plastic tube. All isolates tested were pathogenic to both species of fruit flies. Mortality ranged from 7 to 100% in C. capitata and from 11.4 to 100% in C. rosa var. fasciventris at 4 days post-inoculation. Six isolates, M. anisopliae ICIPE 18, 20, 32, 40, 41 and 62, were highly pathogenic to both C. capitata and C. rosa var. fasciventris. The LT90 values of the most pathogenic isolates ranged between 3-4 days in both insects. Because of the difficulties in rearing C. cosyra, only the isolates that were highly pathogenic to both C. rosa var. fasciventris and C. capitata were tested against adult C. cosyra. They caused mortality of between 72-78% at 4 days post-inoculation. The LT90 values in all the isolates did not exceed 4 days. One of the most pathogenic isolates, M. anisopliae ICIPE 20, was evaluated against C. capitata and C. rosa var. fasciventris in cage experiments using three autoinoculators (maize cob, cheesecloth and Petri dish) in an autoinoculative device consisting of plastic mineral bottle. Mortality of between 70-93% was observed in flies of both species that were captured from the cages and held under laboratory conditions. These results indicate the possibility of fruit fly suppression with entomopathogenic fungi using an autoinoculative device.     

Mortality in Three African Tephritid Fruit Fly Puparia and Adults Caused by the Entomopathogenic Fungi, Metarhizium anisopliae and Beauveria bassiana

The pathogenicity of 13 isolates of Metarhizium anisopliae and two isolates of Beauveria bassiana to Ceratitis capitata and Ceratitis var. rosa fasciventris exposed as late third instar larvae in sand was evaluated in the laboratory. All isolates caused a significant reduction in adult emergence and a corresponding large mortality on puparia of both species. All isolates also induced large deferred mortality in emerging adults following treatment as late third instar larvae. On C. capitata , seven isolates ( M. anisopliae ICIPE 18, 20, 32, 60 and 69 and B. bassiana ICIPE 44 and 82) caused significantly higher mortality on puparia than other isolates. With the exception of ICIPE 32, the other four isolates of M. anisopliae above were the most pathogenic against C. r. fasciventris . Dose-response study carried out with these isolates of M. anisopliae on the two species of flies above plus another species, Ceratitis cosyra showed that the dose-mortality regression lines of ICIPE 18 and 20 were steeper with lower LC 50 values when compared with ICIPE 60 and 69 on the three species. When these two isolates were evaluated with regard to their pathogenicity to different pupal age, adult emergence was found to increase with increasing pupal age with a corresponding decrease in mortality in puparia and emerging adults in the three species of fruit flies. M. anisopliae ICIPE 18 and 20 were equally pathogenic to all pupal ages tested in C. capitata and C. cosyra but ICIPE 18 was more pathogenic to older puparia of C. r. fasciventris than ICIPE 20. Our results suggest that soil inoculation with M. anisopliae under mango trees might form an important component of integrated pest management strategies in areas where these three species of fruit fly coexist.     

Effect of soil temperature and moisture on survival and infectivity of Metarhizium anisopliae to four tephritid fruit fly puparia

The infectivity of 4 isolates of Metarhizium anisopliae to puparia of Ceratitis capitata treated as late third-instar larvae in unsterilized soil was investigated in the laboratory under controlled temperature and moisture. At 20-30 degrees C, mortality in puparia was highest at water potential of -0.1 and -0.01 mega Pascal (MPa) and lowest at water potential of -0.0055 and -0.0035 MPa in all the isolates. In wetter soil however, isolates ICIPE 20 and 60 caused significantly higher mortality than ICIPE 18 and 69. The survival of conidia in drier soil (-0.1 MPa) was not adversely affected at all temperatures. However, in wet soil (-0.0035 MPa) there was drastic reduction in colony counts in ICIPE 18 and 69 at 25 and 30 degrees C but conidial density in ICIPE 20 and 60 remained at the initial level at 14 days after inoculation at all temperatures. When ICIPE 20 was evaluated against three other fruit fly species (Ceratitis cosyra, Ceratitis rosa, and Ceratitis fasciventris), significant reduction in adult emergence and higher pupal mortality occurred in C. cosyra and C. fasciventris than in C. rosa at a combination of 15 and 20 degrees C and -0.1 and -0.0035 MPa. However, at higher temperature and the same moisture level, the isolates were equally pathogenic across the 3 species. It is probable that in addition to pathogen cycling and multiplication from dead infected insects in the soil, a balance between microbial degradation and replenishment of inoculum of virulent isolates occur through fluctuations in, and intricate interactions between temperature and moisture levels. This study is indicative of the potential of using isolate ICIPE 20 for soil inoculation against pupariating third-instar larva of fruit flies, thus providing a novel alternative to chemical soil application.     

Developmental rates at constant temperatures of three economically important Ceratitis spp. (Diptera: Tephritidae) from southern Africa

Three species of Ceratitis MacLeay are of economic importance in southern Africa. To learn more about the influence of temperature on the development of these species, the developmental rates of South African populations of Ceratitis (Ceratitis) capitata (Wiedemann), C. (Pterandrus) rosa Karsch, and C. (Ceratalaspis) cosyra (Walker) were compared at constant temperatures of 14, 18, 22, 26, and 30 degrees C. The duration of each life stage and the percentage survival of the immature life stages of each species were determined. One linear and three nonlinear developmental rate models (Briére, Lactin, and Logan-6) were found to fit the data well and were used to generate the minimum, optimum, and maximum developmental thresholds, in addition to the life cycle thermal constants for the three species. These parameter values were 9.6, 28.5, 33.0, and 338 for C. capitata, 9.7, 28.8, 33.2, and 376 for C. cosyra, and 8.6, 27.7, 33.0, and 429 for C. rosa, respectively. The parameters for C. capitata are similar to those found by other researchers for this species in Reunion but the parameters for C. rosa differ substantially from published values for a Reunion population of this species, suggesting that these are different biotypes. The similarities between the developmental parameters for C. capitata and C. cosyra do not support known differences in the distribution of these species so other limiting factors such as relative humidity and the availability of host species may be important. This finding therefore cautions against basing predictions of potential global distributions of species solely on life table or climatic parameter values.     

Contribution of natural food sources to reproductive behaviour, fecundity and longevity of Ceratitis cosyra, C. fasciventris and C. capitata (Diptera: Tephritidae)

The influence of food sources comprising the natural diet on the reproductive behaviour, fecundity and longevity of three African fruit flies Ceratitis cosyra (Walker), C. fasciventris (Bezzi) and C. capitata (Wiedemann) was investigated. Three natural food sources, varying in protein and sugar content, were evaluated. These included bird droppings (farm chicken), aphid honeydew and guava (Psidium guajava L.) juice. For C. fasciventris and C. capitata, flies fed on a protein-rich diet displayed higher frequency of calling, mating and oviposition than flies fed on a protein-poor diet, whilst for C. cosyra, quality of diet significantly influenced the mating behaviour of the flies, but not the calling and oviposition behaviour. Net fecundity rates were lowest for C. fasciventris and C. capitata when fed only on guava juice (0.1, 2.6 eggs per female, respectively), and higher for those on a diet of honeydew only (9.5, 33.8 eggs per female, respectively) and a combined diet of guava, honeydew and chicken faeces (11.8, 25.8 eggs per female, respectively). For C. cosyra, due to low numbers of eggs collected, no significant differences in fecundity between diets could be detected. All species fed only on a diet of chicken faeces since emergence died within the first three days of adult life without laying eggs, but when carbohydrates were provided by addition of guava juice and honeydew, the longevity of the flies was sustained for more than four weeks after adult emergence. The practical implications of these findings for control purposes are discussed.     

Molecular evaluation of nominal species in the Ceratitis fasciventris, C. anonae, C. rosa complex (Diptera: Tephritidae)

Ceratitis fasciventris, C. anonae and C. rosa form a complex of economically important fruit fly pests infesting a variety of crops in African countries. Hitherto only adult males of these species can be distinguished easily by morphological characters. Other stages cannot, and for some taxa the taxonomic interpretation and species boundaries remain unclear. In order to clarify phylogenetic relationships and taxonomic status of these species, sequences of mitochondrial (16S, COI, ND6) and nuclear markers (period, ITS1) were analysed in specimens of the three morphospecies throughout the distribution of the complex. Maximum likelihood trees did not recover monophyletic groups corresponding to the morphospecies. Conversely, ND6 and COI divided West African C. fasciventris specimens in two consistent and bootstrap supported clades, involving specimens from Benin and from Mali/Ivory Coast, while the nuclear gene fragments per and ITS1 recovered a well-supported clade corresponding to C. fasciventris from Kenya/Uganda. Hence, the phylogenetic relationships and taxonomic interpretation of the complex appear more intricate than previously hypothesised. The current molecular data do not allow to identify C. fasciventris, C. anonae and C. rosa as distinct phylogenetic species but rather suggest that the morphospecies C. fasciventris is itself a complex of cryptic taxa.     

An integrated genetic and cytogenetic map for the Mediterranean fruit fly, <Emphasis Type="Italic">Ceratitis capitata</Emphasis>, based on microsatellite and morphological markers

A genetic map based on microsatellite polymorphisms and visible mutations of the Mediterranean fruit fly (medfly), Ceratitis capitata is presented. Genotyping was performed on single flies from several backcross families. The map is composed of 67 microsatellites and 16 visible markers distributed over four linkage groups. Fluorescence in situ hybridization of selected microsatellite markers on salivary gland polytene chromosomes allowed the alignment of these groups to the second, fourth, fifth and sixth chromosome. None of the markers tested showed segregation either with the X or the third chromosome. However, this map constitutes a substantial starting point for a detailed genetic map of C. capitata. The construction of an integrated map covering the whole genome should greatly facilitate genetic studies and future genome sequence projects of the species.     

Survival and development of different life stages of three Ceratitis spp. (Diptera: Tephritidae) reared at five constant temperatures

Fruit flies (Diptera: Tephritidae) are the most damaging pests on fruit crops on Réunion Island, near Madagascar. Survival and development of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), the Natal fruit fly, C. rosa Karsch and the Mascarenes fruit fly, C. catoirii Guérin-Mèneville were compared at five constant temperatures spanning 15 to 35 degrees C. Durations of the immature stages of C. capitata, C. rosa and C. catoirii ranged from 14.5-63.8, 18.8-65.7 and 16.8-65.8 days, respectively, at 30-15 degrees C. The lower developmental threshold and thermal constant were calculated using the temperature summation model. The thermal constant for total development of the immature stages of C. capitata, C. rosa and C. catoirii were 260, 405 and 356 DD, respectively. Species differed mainly during the larval stages and ovarian maturation period, with smaller differences in the egg stage. Ceratitis rosa appeared to be better adapted to low temperatures than the two other species as it showed a lower larval developmental threshold of 3.1 degrees C compared to 10.2 degrees C for C. capitata and 8.9 degrees C for C. catoirii. Overall, C. catoirii had a low survival rate within the range of temperatures studied. The different responses of the three Ceratitis species to various temperatures explain to some extent their distribution on the island. The results obtained will be used for optimizing laboratory rearing procedures and for constructing computer simulation models to predict fruit fly population dynamics.     

Genetic and molecular investigations on the endogenous mobile elements of non-drosophilid fruitflies

A syndrome of abnormal genetic effects, resembling Drosophila hybrid dysgenesis, occurs in Ceratitis capitata when strains of different origin are mated. The pattern of abnormal traits observed appears to be the phenotypic expression of a complex interacting dysgenic system of inducer and suppressor effects; probably more than one system is activated in the crosses. This suggests that different systems of mobile elements occur in different strains and populations of C. capitata. Using a PCR primer specific to the ITR sequence of a deleted element, full length mariner elements were isolated from C. capitata, Ceratitis rosa, and Trirhithrum coffeae. Very high similarities were found in inter- and intraspecific comparisons of the elements. The majority of these elements contained deletions and frame-shifts. However, one clone Ccmar1.18, from C. capitata, was found to possess an uninterrupted ORF coding for 338 amino acids with ∼60% similarity to the Mos1 element of Drosophila mauritiana. Database searches and phylogenetic analyses showed that the mariner elements isolated in the present study are representatives of Robertson's mellifera mariner subfamily. The copy numbers of the elements within each species are very different, ranging from about 10 in T. coffeae to 5000 in C. rosa. This revised version was published online in August 2006 with corrections to the Cover Date.     

Permanent Genetic Resources added to Molecular Ecology Resources Database 1 December 2009-31 January 2010

This article documents the addition of 220 microsatellite marker loci to the Molecular Ecology Resources Database. Loci were developed for the following species: Allanblackia floribunda, Amblyraja radiata, Bactrocera cucurbitae, Brachycaudus helichrysi, Calopogonium mucunoides, Dissodactylus primitivus, Elodea canadensis, Ephydatia fluviatilis, Galapaganus howdenae howdenae, Hoplostethus atlanticus, Ischnura elegans, Larimichthys polyactis, Opheodrys vernalis, Pelteobagrus fulvidraco, Phragmidium violaceum, Pistacia vera, and Thunnus thynnus. These loci were cross-tested on the following species: Allanblackia gabonensis, Allanblackia stanerana, Neoceratitis cyanescens, Dacus ciliatus, Dacus demmerezi, Bactrocera zonata, Ceratitis capitata, Ceratitis rosa, Ceratits catoirii, Dacus punctatifrons, Ephydatia mülleri, Spongilla lacustris, Geodia cydonium, Axinella sp., Ischnura graellsii, Ischnura ramburii, Ischnura pumilio, Pistacia integerrima and Pistacia terebinthus.     

The ceratotoxin gene family in the medfly Ceratitis capitata and the Natal fruit fly Ceratitis rosa (Diptera: Tephritidae)

Ceratotoxins (Ctxs) are a family of antibacterial sex-specific peptides expressed in the female reproductive accessory glands of the Mediterranean fruit fly Ceratitis capitata. As a first step in the study of molecular evolution of Ctx genes in Ceratitis, partial genomic sequences encoding four distinct Ctx precursors have been determined. In addition, anti-Escherichia coli activity very similar to that of the accessory gland secretion from C. capitata was found in the accessory gland secretion from Ceratitis (Pterandrus) rosa. SDS-PAGE analysis of the female reproductive accessory glands from C. rosa showed a band with a molecular mass (3 kDa) compatible with that of Ctx peptides, also slightly reacting with an anti-Ctx serum. Four nucleotide sequences encoding Ctx-like precursors in C. rosa were determined. Sequence and phylogenetic analyses show that Ctxs from C. rosa fall into different groups as C. capitata Ctxs. Our results suggest that the evolution of the ceratotoxin gene family might be viewed as a combination of duplication events that occurred prior to and following the split between C. capitata and C. rosa. Genomic hybridization demonstrated the presence of multiple Ctx-like sequences in C. rosa, but low-stringency Southern blot analyses failed to recover members of this gene family in other tephritid flies.     

Isolation and characterization of 20 polynucleotide microsatellite markers in a vulnerable Korean snail, <Emphasis Type="Italic">Ellobium chinense,</Emphasis> using 454 pyrosequencing

A small and air-breathing snail, Ellobium chinense (Ellobiidae), is a vulnerable species by International Union for Conservation of Nature (IUCN). To protect and manage habitat and population of E. chinense, microsatellite markers were developed using 454 pyrosequencing and 20 polymorphic microsatellite markers were identified. A total of 146,704 sequences containing a minimum of four repeat motifs (mean, 631 base pairs) were identified from 499,505 reads. Among 80 loci containing more than nine repeat units, 34 primer sets (42.5 %) produced strong PCR products, of which 20 were polymorphic among 48 samples of E. chinense. All loci exhibited high genetic variability, with an average of 18.9 alleles per locus, and the mean observed and expected heterozygosities were 0.65 and 0.90, respectively. In addition, cross-amplification was tested for all 20 loci in the same family species, Melampus sincaporensis. None of the primer pairs resulted in effective amplification, which might be due to their high mutation rates. Our work demonstrated the utility of next-generation 454 sequencing as a method for the rapid and cost-effective identification of microsatellites. The high degree of polymorphism exhibited by the 20 newly developed microsatellites will be useful in future conservation genetic studies of this species.     

Microsatellite markers for the study of cetacean populations

Microsatellites are one of the most important classes of nuclear genetic markers and offer many advantages for the study of marine mammals. Here we describe the isolation and characterization of 12 cetacean microsatellites which are then tested across 30 different cetacean species. For around half the species tested, five or more polymorphic loci were identified. Since many species were represented by only one or two specimens, this figure is likely to underestimate the usefulness of these markers. No relationship was found between microsatellite repeat length and proportion of species which gave polymorphic products.     

Development of a diagnostic DNA probe for the fruit flies Ceratitis capitata and Ceratitis rosa (Diptera: Tephritidae) using amplified fragment-length polymorphism

The AFLP technique (amplified fragment-length polymorphism) was employed to identify and isolate species specific markers in tephritids. We have found that the technique has good potential for this purpose, with the only difficult part being the reamplification of AFLP fragments from silver stained gels. Cloning of putative species-specific markers and genomic dot blot hybridizations resulted in the development of diagnostic probes for tephritid identification. A repetitive DNA sequence from the genome of Ceratitis capitata (Wiedemann) was isolated. This sequence rapidly and reliably identified C. capitata and C. rosa Karsch in a collection of closely related and outgroup species tested in this study. Although this probe has been developed for C. capitata and C. rosa, the proposed methodology can be applied to any group of organisms.     

Exceptional longevity in the tephritid, Ceratitis rosa, a close relative of the Mediterranean fruit fly

This study shows that the fruit fly, Ceratitis rosa (Karsch), has a significantly longer life span than the medfly, C. capitata (Wiedemann); the species used as a model organism for the demographics of insect aging. This was somewhat surprising given that both have similar distributions and overlapping niches. We postulate that the greater longevity of C. rosa is related to the fact that it can occupy colder habitats where the availability of suitable host plants may be very unpredictable in both time and space.     

Microsatellite evolution--a reciprocal study of repeat lengths at homologous loci in cattle and sheep

The application of microsatellites in evolutionary studies requires an understanding of the patterns governing their evolution in different species. The finding that homologous microsatellite loci are longer, i.e., containing more repeat units, in human and in other primates has been taken as evidence for directional microsatellite evolution and for a difference in the rate of evolution between species. However, it has been argued that this finding is an inevitable consequence of biased selection of longer-than-average microsatellites in human, because cloning procedures are adopted to generate polymorphic and, hence, long markers. As a test of this hypothesis, we conducted a reciprocal comparison of the lengths of microsatellite loci in cattle and sheep using markers derived from the bovine genome as well as the ovine genome. In both cases, amplification products were longer in the focal species, and loci were also more polymorphic in the species from which they were originally cloned. The crossing pattern that we found suggests that interspecific length differences detected at homologous microsatellite loci are the result of biased selection of loci associated with cloning procedures. Hence, comparisons of microsatellite evolution between species are flawed unless they are based on reciprocal analyses or on genuinely random selection of loci with respect to repeat length.      

Comparison of random and SSR-enriched shotgun pyrosequencing for microsatellite discovery and single multiplex PCR optimization in Acacia harpophylla F. Muell. Ex Benth

Streamlining the development and genotyping of microsatellites in species for which no genetic information is available represents an important technical challenge to overcome in order to enable mainstream application of state-of-the-art population genetic analysis techniques in nonmodel organisms. Using the example of Acacia harpophylla, an acacia tree endemic of north-eastern Australia, we show that high-throughput shotgun pyrosequencing technology, so-called second-generation sequencing, reduces time and cost of microsatellite marker discovery in nonmodel organisms and of their large-scale typing in natural populations. We found that 0.5% of short sequence reads generated on 454 Genome Sequencer FLX Titanium from random genome sampling and 2.2% of reads generated with prior microsatellite enrichment yielded microsatellite markers with designed polymerase chain reaction (PCR) primers, suggesting that enrichment increases efficiency of pyrosequencing when microsatellite discovery is the primary goal. Using stringent selection criteria to facilitate downstream PCR multiplex design, we identified 1435 microsatellite loci with designed primers from a total of 200,908 short sequence reads. From a subset of 96 loci tested for amplification, 38 were validated for population genetics applications, leading to the optimization of a cost-effective multiplex PCR protocol for the simultaneous typing of nine microsatellites in natural populations of A. harpophylla.     

Exploiting dinucleotide microsatellites conserved among mammalian species

Dinucleotide microsatellites are useful for gene mapping projects. Depending upon definition of conservation, published estimates of dinucleotide microsatellite conservation levels vary dramatically (30% to 100%). This study focused on well-characterized genes that contain microsatellites in the human genome. The objective was to examine the feasibility of developing microsatellite markers within genes on the basis of the assumption of microsatellite conservation across distantly related species. Eight genes (Gamma-actin, carcinoembryonic antigen, apolipoprotein A-II, cardiac beta myosin heavy chain, laminin B2 chain, MHC class I CD8 alpha chain, c-reactive protein, and retinoblastoma susceptibility protein) containing large dinucleotide repeat units (N ≥ 15), complete genomic structure information, and homologous gene sequences in a second species were selected. Heterologous primers were designed from conserved exon sequences flanking a microsatellite motif. PCR products from bovine and porcine genomic DNA were tested for the presence of microsatellite sequences by Southern blot hybridization with biotin-labeled (CA)₁₂ oligonucleotides. Fragments containing microsatellites were cloned and sequenced. Homology was verified by sequence comparisons between human and corresponding bovine or porcine fragments. Four of sixteen (25%) cross-amplified PCR products contained dinucleotide repetitive sequences with repeat unit lengths of 5 to 23. Two dinucleotide repetitive sequences showed microsatellite length polymorphism, and an additional sequence displayed single-strand conformational polymorphism. Results from this study suggest that exploitation of conserved microsatellite sequences is a useful approach for developing specific genetic markers for comparative mapping purposes. Received: 7 July 1995 / Accepted: 28 September 1995     

Sequence characterization of microsatellites in diploid and polyploid Ipomoea

 The objectives of the present study were to evaluate the inheritance and nucleotide sequence profiles of microsatellite genetic markers in hexaploid sweetpotato [Ipomoea batatas (L.) Lam.] and its putative tetraploid and diploid ancestors, and to test possible microsatellite mutation mechanisms in polyploids by direct sequencing of alleles. Sixty three microsatellite loci were isolated from genomic libraries of I. batatas and sequenced. PCR primers were designed and used to characterize microsatellite loci in two hexaploid I. batatas populations, a tetraploid Ipomoea trifida population, and a diploid I. trifida population. Nine out of the sixty three primer pairs tested yielded a clearly discernible, heritable banding pattern; five showed Mendelian segregation. All other primer pairs produced either smeared banding patterns, which could not be scored, or no bands at all in I. batatas. All of the primers which produced discernible banding patterns from I. batatas also amplified products of similar size in tetraploid and diploid I. trifida accessions. The sequence analysis of several alleles in the three species showed differences due to mutations in the repeat regions consistent with small differences in the repeat number. However, in some cases insertions/deletions and base substitutions in the microsatellite flanking regions were responsible for polymorphisms in both polyploid and diploid species. These results provide strong empirical evidence that complex genetic mechanisms are responsible for SSR allelic variation in Ipomoea. Four I. batatas microsatellite loci showed polysomic segregation fitting tetraploid segregation ratios. To our knowledge this is the first report of segregation ratios for microsatellites markers in polyploids. Received: 4 January 1999 / Accepted: 4 January 1999