Genetic structure analysis of natural <Emphasis Type="Italic">Sargassum muticum</Emphasis> (Fucales,Phaeophyta) populations using RAPD and ISSR markers

Sargassum muticum is important in maintaining the structure and function of littoral ecosystems, and is used in aquaculture and alginate production, however, little is known about its population genetic attributes. In this study, random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR) markers were used to investigate the genetic structure of four populations of S. muticum and one outgroup of S. fusiforme (Harv.) Setchell from Shandong peninsula of China. The selected 24 RAPD primers and 19 ISSR primers amplified 164 loci and 122 loci, respectively. Estimates of genetic diversity with different indicators (P%, percentage of polymorphic loci; H, the expected heterozygosity; I, Shannon’s information index) revealed low or moderate level of genetic variations within each S. muticum population, and a high level of genetic differentiations were determined with pairwise unbiased genetic distance (D) and fixation index (F _ST ) among the populations. The Mantel test showed that two types of matrices of D and F _ST were highly correlated whether from RAPD (r = 0.9706, P = 0.009) or ISSR data (r = 0.9161, P = 0.009). Analysis of molecular variance (AMOVA) was conducted to apportion the variations among and within the S. muticum populations. It indicated that variations among populations were higher than those within populations, being 55.82% verse 44.18% by RAPD and 55.21% verse 44.79% by ISSR, respectively. Furthermore, the Mantel test suggested that genetic differentiations among populations were related to the geographical distances (r > 0.6), namely, conformed to the IBD (isolation by distance) model, as expected from UPGMA (unweighted pair group method with arithmetic averages) cluster analysis. On the whole, the high genetic structuring among the four S. muticum populations along the distant locations was clearly indicated in RAPD and ISSR analyses (r > 0.9, P < 0.05) in our study.     

Population structure of red-cockaded woodpeckers in south Florida: RAPDs revisited

Six south Florida populations of the endangered red-cockaded woodpecker (Picoides borealis) were sampled to examine genetic diversity and population structure in the southernmost portion of the species' range relative to 14 previously sampled populations from throughout the species range. Random amplified polymorphic DNA (RAPD) analyses were used to evaluate the populations (n= 161 individuals, 13 primers, one band/primer). Results suggested that south Florida populations have significant among-population genetic differentiation (F_ST= 0.17, P < 0.000), although gene flow may be adequate to offset drift (N_m= 1.26). Comparison of Florida populations with others sampled indicated differentiation was less in Florida (F_ST for all populations = 0.21). Cluster analyses of all 20 populations did not reflect complete geographical predictions, although clustering of distant populations resulted in a significant correlation between genetic distance and geographical distance. Overall, results suggest populations in south Florida, similar to the remainder of the species, have low genetic diversity and high population fragmentation. Exact clustering of distant populations supports the ability of RAPDs to differentiate populations accurately. Our results further support past management recommendations that translocations of birds among geographically proximate populations is preferable to movement of birds between distant populations.     

Patterns of Genetic Variation in Swertia przewalskii, an Endangered Endemic Species of the Qinghai-Tibet Plateau

Swertia przewalskii Pissjauk. (Gentianaceae) is a critically endangered and endemic plant of the Qinghai-Tibet Plateau in China. RAPD and ISSR analyses were carried out on a total of 63 individuals to assess the extent of genetic variation in the remaining three populations. Percentage of polymorphic bands was 94% (156 bands) for RAPD and 96% (222 bands) for ISSR. A pairwise distance measure calculated from the RAPD and ISSR data was used as input for analysis of molecular variance (AMOVA). AMOVA indicated that a high proportion of the total genetic variation (52% for RAPD and 56% for ISSR) was found among populations; pairwise Φ _ST comparisons showed that the three populations examined were significantly different (p < 0.001). Significant genetic differentiation was found based on different measures (AMOVA and Hickory θ_B) in S. przewalskii (0.52 on RAPD and 0.56 on ISSR; 0.46 on RAPD and 0.45 on ISSR). The differentiation of the populations corresponded to low average gene flow (0.28 based on RAPD and 0.31 based on ISSR), whereas genetic distance-based clustering and coalescent-based assignment analyses revealed significant genetic isolation among populations. Our results indicate that genetic diversity is independent of population size. We conclude that although sexual reproduction and gene flow between populations of S. przewalskii are very limited, they have preserved high levels of genetic diversity. The main factors responsible for the high level of difference among populations are the isolation and recent fragmentation under human disturbance.     

Evolutionary implications of allozyme and RAPD variation in diploid populations of dioecious buffalograss Buchloë dactyloides

Buffalograss, Buchloë dactyloides, is widely distributed throughout the Great Plains of North America, where it is an important species for rangeland forage and soil conservation. The species consists of two widespread polyploid races, with narrowly endemic diploid populations known from two regions: central Mexico and Gulf Coast Texas. We describe and compare the patterns of allozyme and RAPD variation in the two diploid races, using a set of 48 individuals from Texas and Mexico (four population samples of 12 individuals each). Twelve of 22 allozyme loci were polymorphic, exhibiting 35 alleles, while seven 10-mer RAPD primers revealed 98 polymorphic bands. Strong regional differences were detected in the extent of allozyme polymorphism: Mexican populations exhibited more internal gene diversity (H_e= 0.20, 0.19) than did the Texan populations (H_e= 0.08, 0.06), although the number of RAPD bands in Texas (n= 62) was only marginally smaller than in Mexico (n= 68). F-statistics for the allozyme data, averaged over loci, revealed strong regional differentiation (mean F_RT=+ 0.30), as well as some differentiation among populations within regions (mean F_PR=+ 0.09). In order to describe and compare the partitioning of genetic variation for multiple allozyme and RAPD loci, we performed an Analysis of Molecular Variance (AMOVA). AMOVA for both allozyme and RAPD data revealed similar qualitative patterns: large regional differences and smaller (but significant) population differences within regions. RAPDs revealed greater variation among regions (58.4% of total variance) than allozymes (45.2%), but less variation among individuals within populations (31.9% for RAPDs vs. 45.2% for allozymes); the proportion of genetic variance among populations within regions was similar (9.7% for RAPDs vs. 9.6% for allozymes). Despite this large-scale concordance of allozyme and RAPD variation patterns, multiple correlation Mantel techniques revealed that the correlations were low on an individual by individual basis. Our findings of strong regional differences among the diploid races will facilitate further study of polyploid evolution in buffalograss.     

Use of RAPD and ISSR Markers in Detection of Genetic Variation and Population Structure among Fusarium oxysporum f. sp. ciceris Isolates on Chickpea in Turkey

Genetic variation among the isolates of Fusarium oxysporum f. sp. ciceris, the causal agent of chickpea wilt worldwide, was analysed using pathogenicity tests and molecular markers – random amplified polymorphic DNA (RAPD) and inter‐simple sequence repeat (ISSR) polymorphism. Hundred and eight isolates were obtained from diseased chickpea plants in 13 different provinces of Turkey, out of which 74 isolates were assessed using 30 arbitrary decamer primers and 20 ISSR primers. Unweighted pair‐grouped method by arithmetic average cluster analysis of RAPD, ISSR and RAPD + ISSR datasets provided a substantially similar discrimination among Turkish isolates and divided into three major groups. Group 1, 2 and 3 consisted of 41, 18 and 15 isolates, respectively. These methods revealed a considerable genetic variation among Turkish isolates, but no correlation with regard to the clustering of isolates from different geographic regions. Analysis of molecular variance confirmed that most genetic variability resulted from the differences among isolates within regions. Our results also indicated that the low‐genetic differentiation (F_ST) and high gene flow (Nm) among populations had a significant effect on the emergence and evolutionary development of F. oxysporum f. sp. ciceris. This is the first report on genetic diversity and population structure of F. oxysporum isolates on chickpea in Turkey.     

Migration barriers protect indigenous brown trout (<Emphasis Type="Italic">Salmo trutta</Emphasis>) populations from introgression with stocked hatchery fish

Brown trout populations in the Belgian rivers Scheldt and Meuse have been intensively stocked in the past decades, often with material of uncertain origin. Moreover, the species habitat has become increasingly fragmented, preventing gene flow between neighboring populations. We assessed how this impacted genetic diversity and population structure by analyzing 12 wild populations (total n=309) and seven hatchery stocks (n=200) at the mitochondrial control region with SSCP and at 27 RAPD loci. Historical records indicate that brown trout from distant locations have been used to supplement hatchery stocks; nevertheless we detected non-Atlantic mitochondrial genomes in only one population of the Scheldt basin and in one hatchery. In general, the hatchery samples displayed a higher genetic diversity and differentiated less among each other (global F_ST(mtDNA)=0.311/F_ST(RAPD)=0.029) compared to the wild populations (global F_ST(mtDNA)=0.477/F_ST(RAPD)=0.204). This is due to frequent exchanges between hatcheries and regular supplementation from several indigenous populations. Gene pools present in most downstream sections from tributaries of the Meuse were similar to each other and to the hatchery samples, despite the presence of migration barriers. Assignment analyses indicated that the contribution of hatchery material to the upstream parts was limited or even completely absent in populations separated by a physical barrier. Intensive stocking and exchange between hatcheries has homogenized the downstream sections of the Meuse River, whereas the migration barriers preserved the indigenous upstream populations. As such, uncontrolled removal of barriers might result in an irreversible loss of the remnant indigenous gene pools.     

Population differentiation in randomly amplified polymorphic DNA of red-cockaded woodpeckers Picoides borealis

Random amplified polymorphic DNA (RAPD) phenotypes generated by 13 primers were scored for 101 individuals in 14 populations of the endangered red-cockaded woodpecker Picoides borealis. Although no population-specific markers were found, the frequencies of several markers differed significantly among populations. Application of the recently developedamova method (analysis of molecular variance; Excoffier, Smouse & Quattro 1992) showed that more than 90% of phenotypic variance occurred among individuals within populations; of the remaining variance, half was attributed among groups of geographically adjacent populations and half among populations within those groups. The statistical significance of these patterns was supported by Monte Carlo sampling simulations and permutation tests. Estimation of allele frequencies from phenotypes provided somewhat weaker evidence for population structure, although among-population variance in allele frequencies was detectable (F_st= 0.19; x²₁₆₉= 509.3, P < 0.0001). Upgma cluster analyses based on Rogers' (1972) genetic distance revealed grouping of some geographically proximate populations. A Mantel test indicated a positive (r = 0.16), although not significant, correlation between geographic and genetic distances. We compared a subset of our RAPD data with data from a previous study that used allozymes (Stangel, Lennartz & Smith 1992). RAPD (n= 75) and allozyme (n= 245) results based on samples from the same ten populations showed similar patterns. Our study indicates that RAPDs can be helpful in differentiating populations at the phenotypic level even when small sample sizes, estimation bias, and inability to test for Hardy-Weinberg equilibrium complicate the genotypic interpretation. Lack of large differences among populations of red-cockaded woodpeckers may allow flexibility in overpopulation translocations, provided factors such as habitat preference, latitudinal direction of translocation, and status of donor populations are considered.     

Genetic variation for sexual dimorphism in flower size within and between populations of gynodioecious Thymus vulgaris

There has been very little empirical study of quantitative genetic variation in flower size in sexually dimorphic plant species, despite the frequent occurrence of flower size differences between sexual phenotypes. In this study we quantify the nature of quantitative flower size variation in females and hermaphrodites of gynodioecious Thymus vulgaris. In a field study, females had significantly smaller flowers than hermaphrodites, and the degree of flower size dimorphism varied significantly among populations. To quantify the genetic basis of flower size variation we sampled maternal progeny from 10 F₀ females in three populations (across the range of variation in flower size in the field), performed controlled crosses on F₁ offspring in the glasshouse and grew F₂ progeny to flowering in uniform field conditions. A significant population * sex interaction was again observed, hence the degree of sexual dimorphism shows genetic variation among populations. A significant family * sex interaction was also observed, indicating that the degree of sexual dimorphism shows genetic variation among families. Females showed significantly greater variation among populations and among families than hermaphrodites. Female flower size varied significantly depending on the degree of stamen abortion, with morphologically intermediate females having flowers more similar to hermaphrodites than to other females. The frequency of female types that differ in the degree of stamen abortion varied among populations and families and mean family female flower size increased as the proportion of intermediate female types increased across families. Variation in the degree of flower size dimorphism thus appears to be a result of variation in the degree of stamen abortion in females, the potential causes of which are discussed.     

Genetic diversity of insular natural populations of <Emphasis Type="Italic">Festuca pratensis</Emphasis> Huds.: RAPD analysis

In natural populations of Festuca pratensis Huds. from the islands of Onega Lake, the level of genetic diversity was evaluated. In three populations variability of 64 RAPD loci was tested. The level of genetic diversity (P _95% = 30.2; H _exp = 0.093) was low for a cross-pollinating plant species. Furthermore, genetic similarity between the plants from insular populations was found to be high (I _N = 0.887). It was demonstrated that genetic variation among the population accounted for at most 5.3% of total genetic diversity, which, however, was higher than the F _ST values for continental populations (F _ST = 0.022). It was suggested that specific features of the genetic structure of insular population, i.e., low gene diversity within the populations along with high differentiation among the populations, were caused by the gene flow attenuation, as a result of isolation, and intensification of inbreeding. These features had negative effect on total population adaptation.     

Population genetic structure of <Emphasis Type="Italic">Sargassum thunbergii</Emphasis> (Fucales,Phaeophyta) detected by RAPD and ISSR markers

Genetic variation of four populations of Sargassum thunbergii (Mert.) O. Kuntze and one outgroup of S. fusiforme (Harv.) Setchell from Shandong peninsula of China was studied with random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR) markers. A total of 28 RAPD primers and 19 ISSR primers were amplified, showing 174 loci and 125 loci, respectively. Calculation of genetic diversity with different indicators (P%, percentage of polymorphic loci; H, the expected heterozygosity; I, Shannon’s information index) revealed low or moderate levels of genetic variations within each S. thunbergii population. High genetic differentiations were determined with pairwise Nei’s unbiased genetic distance (D) and fixation index (F _ST ) between the populations. The Mantel test showed that two types of matrices of D and F _ST were highly correlated, whether from RAPD or ISSR data, r = 0.9310 (P  = 0.008) and 0.9313 (P = 0.009) respectively. Analysis of molecular variance (AMOVA) was used to apportion the variations between and within the S. thunbergii populations. It indicated that the variations among populations were higher than those within populations, being 57.57% versus 42.43% by RAPD and 59.52% versus 40.08% by ISSR, respectively. Furthermore, the Mantel test suggested that the genetic differentiations between the four populations were related to the geographical distances (r > 0.5), i.e., they conformed to the IBD (isolation by distance) model, as expected from UPGMA (unweighted pair group method with arithmetic averages) cluster analysis. As a whole, the high genetic structuring between the four S. thunbergii populations along distant locations was clearly indicated in the RAPD and ISSR analyses (r > 0.8) in our study.     

Mapping of the <Emphasis Type="Italic">multifoliate pinna</Emphasis> (<Emphasis Type="Italic">mfp</Emphasis>) leaf-blade morphology mutation in grain pea <Emphasis Type="Italic">Pisum sativum</Emphasis>

The multifoliate pinna (mfp) mutation alters the leaf-blade architecture of pea, such that simple tendril pinnae of distal domain are replaced by compound pinna blades of tendrilled leaflets in mfp homozygotes. The MFP locus was mapped with reference to DNA markers using F₂ and F_2:5 RIL as mapping populations. Among 205 RAPD, 27 ISSR and 35 SSR markers that demonstrated polymorphism between the parents of mapping populations, three RAPD markers were found linked to the MFP locus by bulk segregant analyses on mfp/mfp and MFP/MFP bulks assembled from the F_2:5 population. The segregational analysis of mfp and 267 DNA markers on 96 F₂ plants allowed placement of 26 DNA markers with reference to MFP on a linkage group. The existence of common markers on reference genetic maps and MFP linkage group developed here showed that MFP is located on linkage group IV of the consensus genetic map of pea.     

RAPD variation within and among natural populations of outcrossing willow-leaved foxglove (Digitalis obscura L.)

 Random amplified polymorphic DNA (RAPD) markers were used to assess levels and patterns of genetic diversity in Digitalis obscura L. (Scrophulariaceae), an outcrossing cardenolide-producing medicinal plant species. A total of 50 plants from six natural populations on the Iberian Peninsula were analysed by six arbitrarily chosen decamer primers resulting in 96 highly reproducible RAPD bands. To avoid bias in parameter estimation, analyses of population genetic structure were restricted to bands (35 of 96) whose observed frequencies were less than 1–3/n in each population. The analysis of molecular variance (AMOVA) with distances among individuals corrected for the dominant nature of RAPDs (genotypic analysis) showed that most of the variation (84.8%) occurred among individuals within populations, which is expected for an outcrossing organism. Of the remaining variance, 9.7% was attributed to differences between regions, and 5.5% for differences among populations within regions. Estimates of the Wright, Weir and Cockerham and Lynch and Milligan F_ST from null-allele frequencies corroborated AMOVA partitioning and provided significant evidence for population differentiation in D. obscura. A non-parametric test for the homogeneity of molecular variance (HOMOVA) also showed significant differences in the amount of genetic variability present in the six populations. UPGMA cluster analyses, based on Apostol genetic distance, revealed grouping of some geographically proximate populations. Nevertheless, a Mantel test did not give a significant correlation between geographic and genetic distances. This is the first report of the partitioning of genetic variability within and between populations of D. obscura and provides important baseline data for optimising sampling strategies and for conserving the genetic resources of this medicinal species. Received: 7 September 1998 / Accepted: 28 November 1998     

Genetic diversity analysis of Rhododendron aureum Georgi (Ericaceae) located on Changbai Mountain using ISSR and RAPD markers

Rhododendron aureum Georgi (Ericaceae) is a perennial alpine shrub endemic to Changbai Mountain in China. We used ISSR and RAPD markers to describe the diversity and genetic structure within and among four natural populations located at different altitudes. DNA from 66 individuals was amplified with ten ISSR markers and seven RAPD markers. High genetic diversity was observed by these two techniques at the species level. The genetic diversity of populations increased with altitudinal gradients from low to high. The coefficient of gene differentiation (G_ST 0.3652 in ISSR and 0.2511 in RAPD) and AMOVA analysis revealed that most genetic diversity was distributed within populations (61.96% in ISSR and 70.23% in RAPD). The estimate of gene flow based on G_ST was 0.8690 in ISSR and 1.4910 in RAPD. The UPGMA clustering results using ISSR and RAPD showed that all individuals from the same altitude were gathered together, and the two populations (TYD2a and YHLa) from middle altitudes always clustered together. Compared with populations from different altitudes, similar genetic diversity and low genetic differentiation were obtained from populations at the same altitudes, as revealed by ISSR markers. In addition to the reproductive strategy of R. aureum, these data highlight that local environmental conditions may play an important role in shaping the diversity and genetic structure of this species.     

Estimations of number of active loci,dominance and heritability in polygenic inheritance of gregarious behavior inMuscidifurax raptorellus [Hymenoptera: Pteromalidae]

Estimates of the minimum number of genetic loci governing expressions of gregarious oviposition inMuscidifurax raptorellus Kogan & Legner were enabled by the verification of recombinant males, which were secured from virgin hybrid females, formed by crossing cohorts from solitary and gregarious populations. Examinations of parasitization behavior in female progeny that had F₁ male fathers indicated the presence of hybrids among the males. Estimates of gene number, made on the basis of variances in P₁, F₁, F₂ and backcross progeny, and by observing behavior in second and third order backcrosses, ranged from two to 19, with most between two and five. However, backcrossing data suggested that at least eight loci were actively segregating for this characteristic. Semi-dominance of the solitary trait (D=0.63 to 0.84), and unequal gene effects probably caused these gene estimated to be lower than the actual number. Estimates of the coefficient of heritability, in the broad sense based on parental and F₁ and F₂ variances indicated that variability of gregarious behavior in the experimental environment was influenced >60% by genotypic factors, offspring-parent regression analyses gave estimates >38%.      

Genomic and chemical evidence for local adaptation in resistance to different herbivores in Datura stramonium

Because most species are collections of genetically variable populations distributed to habitats differing in their abiotic/biotic environmental factors and community composition, the pattern and strength of natural selection imposed by species on each other's traits are also expected to be highly spatially variable. Here, we used genomic and quantitative genetic approaches to understand how spatially variable selection operates on the genetic basis of plant defenses to herbivores. To this end, an F₂ progeny was generated by crossing Datura stramonium (Solanaceae) parents from two populations differing in their level of chemical defense. This F₂ progeny was reciprocally transplanted into the parental plants’ habitats and by measuring the identity by descent (IBD) relationship of each F₂ plant to each parent, we were able to elucidate how spatially variable selection imposed by herbivores operated on the genetic background (IBD) of resistance to herbivory, promoting local adaptation. The results highlight that plants possessing the highest total alkaloid concentrations (sum of all alkaloid classes) were not the most well-defended or fit. Instead, specific alkaloids and their linked loci/alleles were favored by selection imposed by different herbivores. This has led to population differentiation in plant defenses and thus, to local adaptation driven by plant-herbivore interactions.     

Molecular variation and population structure in Elymus trachycaulus and comparison with its morphologically similar E. alaskanus

Random amplified polymorphic DNA (RAPD) markers were used to determine the levels and pattern of molecular variation in four populations of Elymus trachycaulus, and to estimate genetic similarity among different populations of E. trachycaulus from British Columbia and the Northwest Territories and one population of Elymus alaskanus from the Northwest Territories. Based on 124 RAPD bands (loci), mean percent polymorphic loci for E. trachycaulus (P_P) was 67.4% (a range 41.2% to 86.3%), and mean gene diversity (H_e) for E. trachycaulus species was 0.23 (range 0.18 to 0.27). The total genetic diversity was 0.32. Differentiation among populations was 31% (F_ST = 0.31) with most of the genetic variation found within populations (69%). This pattern of genetic variation was different from that reported for inbred species in general.The authors are very grateful to Michael Bond for excellent Laboratory assistance, to Dr. Mary Barkworth for her encouragement. This study was supported by a Natural Science and Engineering Research Council (NSERC) discovery grant and by a Saint Marys University Internal grant to G.S.     

Conservation genetics of endangeredBrasenia schreberi based on RAPD and AFLP markers

Brasenia schreberi J.F. Gmelin is a declared endangered species found in the lakes and ponds of South Korea. For planning its conservation strategy, we examined the genetic diversity within and among six populations, using randomly amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP). Polymorphisms were more frequently detected per loci with AFLP (69.3%) than RAPD (36.8%). High genetic diversity was recognized within populations: polymorphic loci (PPL) values ranged from 36.3% in the CJM population to 74.5% in the GGT population, with a mean value of 47.8% based on AFLP markers. Great genetic differentiation (θ^B) was detected among the six populations (0.670 on RAPD and 0.196 on AFLP), and we calculated a low rate of gene flow (N_em), i.e., 0.116 on RAPD and 0.977 on AFLP. Furthermore, a Mantel test revealed that no correlation existed between genetic distances and geographical distances among the six local populations, based on RAPD or AFLP markers. These results are attributed to a number of factors, including an insufficient length of time for genetic diversity to be reduced following a natural decline in population size and isolation, adaptation of the genetic system to small population conditions, and a restricted gene flow rate. Based on both its genetic diversity and population structure, we suggest that a strategy for conserving and restoringB. schreberi must focus on maintaining historical processes, such as high levels of outbreeding, while monitoring increased gene flow among populations. This is because a reduction in genetic diversity as a result of genetic drift is undesirable.     

Local selection modifies phenotypic divergence among Rana temporaria populations in the presence of gene flow

In ectotherms, variation in life history traits among populations is common and suggests local adaptation. However, geographic variation itself is not a proof for local adaptation, as genetic drift and gene flow may also shape patterns of quantitative variation. We studied local and regional variation in means and phenotypic plasticity of larval life history traits in the common frog Rana temporaria using six populations from central Sweden, breeding in either open‐canopy or partially closed‐canopy ponds. To separate local adaptation from genetic drift, we compared differentiation in quantitative genetic traits (Q_ST) obtained from a common garden experiment with differentiation in presumably neutral microsatellite markers (F_ST). We found that R. temporaria populations differ in means and plasticities of life history traits in different temperatures at local, and in F_ST at regional scale. Comparisons of differentiation in quantitative traits and in molecular markers suggested that natural selection was responsible for the divergence in growth and development rates as well as in temperature‐induced plasticity, indicating local adaptation. However, at low temperature, the role of genetic drift could not be separated from selection. Phenotypes were correlated with forest canopy closure, but not with geographical or genetic distance. These results indicate that local adaptation can evolve in the presence of ongoing gene flow among the populations, and that natural selection is strong in this system.     

Genetic diversify among Balkan trout populations based on RAPD analysis

Random amplified polymorphic DNA (RAPD) markers were used to estimate the population structure and phylogenetic relationships among samples of the Salmo trutta complex that inhabit the Balkan Peninsula. Five random oligodecamers were selected to amplify DNA from 140 fish from seven populations. Using these primers, 55 discernible DNA fragments were generated, of which 50 (90.91%) were polymorphic. The statistical results indicated that there was low genetic diversity within populations (with an average percentage of polymorphic bands (P) of 11.69% and a Nei’s genetic diversity index (h) of 0.035), but at the same time high genetic differentiation among populations (F _ST = 0.89). The distribution of genetic diversity among Balkan trout may result from their evolutionary history and reflects genetic drift coupled with bottleneck phenomena. Overall, RAPDs proved valuable tools for quick and reliable stock discrimination and provided information that might be useful regarding conservation and management of trout.     

Identification and application of RAPD markers for anthracnose resistance in water yam (Dioscorea alata)

Anthracnose, caused by Colletotrichum gloeosporioides, is the most severe foliar disease of water yam (Dioscorea alata) worldwide. The tetraploid breeding line, TDa 95/00328, is a source of dominant genetic resistance to the moderately virulent fast growing salmon (FGS) strain of C. gloeosporioides. Bulked segregant analysis was used to search for random amplified polymorphic DNA (RAPD) markers linked to anthracnose resistance in F₁ progeny derived from a cross between TDa 95/00328 and the susceptible male parent, TDa 95–310. Two hundred and eighty decamer primers were screened using bulks obtained from pooled DNA of individuals comprising each extreme of the disease phenotype distribution. A single locus that contributes to anthracnose resistance in TDa 95/00328 was identified and tentatively named Dcg‐1. We found two RAPD markers closely linked in coupling phase with Dcg‐1, named OPI7₁₇₀₀ and OPE6₉₅₀, both of which were mapped on the same linkage group. OPI7₁₇₀₀ appeared tightly linked to the Dcg‐1 locus; it was present in all the 58 resistant F₁ individuals and absent in all but one of the 13 susceptible genotypes (genetic distance of 2.3 cM). OPE6₉₅₀ was present in 56 of the 58 resistant progeny and only one susceptible F₁ plant showed this marker (6.8 cM). Both markers successfully identified Dcg‐1 in resistant D. alata genotypes among 34 breeding lines, indicating their potential for use in marker‐assisted selection. OPI7₁₇₀₀ and OPE6₉₅₀ are the first DNA markers for yam anthracnose resistance. The use of molecular markers presents a valuable strategy for selection and pyramiding of anthracnose resistance genes in yam improvement.