Seedlings Of Genotypes Research Articles

Haplotype dictionary for the Rht-1 loci in wheat

The introduction of Reduced height (Rht)-B1b and Rht-D1b into bread wheat (Triticum aestivum) varieties was a key component of the 'green revolution' and today these alleles are the primary sources of semi-dwarfism in wheat. The Rht-1 loci encode DELLA proteins, which are transcription factors that affect plant growth and stress tolerance. In bread wheat, Rht-D1b and Rht-B1b influence resistance to the disease Fusarium Head Blight. To identify Rht-1 variants, locus specific primers were developed and used to sequence the entire open reading frame (ORF) and 1.7kb of the 5' and 0.5kb of the 3' flanking regions of Rht-A1 (Rht-A1+f), Rht-B1 (Rht-B1+f), and Rht-D1 (Rht-D1+f) in bread wheat (36 sequences from each genome) and tetraploid and diploid wheat (TDW) (one to three sequences from each genome). Among the bread wheat accessions, the Rht-A1+f and Rht-D1+f sequences contained relatively low genetic diversity and few haplotypes relative to the Rht-B1+f sequences. The TDW accessions were relatively rich in genetic diversity and contained the majority of the polymorphic sites. Novel polymorphisms, relative to 'Chinese Spring', discovered among the accessions include 160 and 197bp insertions 5' of Rht-B1 and a frameshift in the Rht-B1 ORF. Quantitative real-time PCR using shoot and leaf tissue from 5-day-old seedlings of genotypes lacking or containing the 5' insertions revealed no major effect on Rht-B1 transcript accumulation. This research provides insights into the genetic diversity present at the Rht-1 loci in modern bread wheat and in relation to ancestral wheat accessions.

Antioxidant enzyme and morphological characteristics of roots of three Nicotiana Tabacum L. genotype seedlings under chilling stress

In order to study the morphological and physiological ecological response of root of Flue-cured tobacco seedling after low temperature stress, this experiment was conducted with different stressful period which was 2, 4 and 6 days under 5 to 7°C (day) by the material named Yunyan87, Msk326 and Yunyan85, respectively. The results showed that comparing with favorable temperature (23 to 25°Cday), activities of superoxide dismutase (SOD) and peroxidase (POD) and ascorbate peroxidase (CAT) had different change trends with difference variety, in which three parameters increased for YY87, and except activities of SOD rise for YY85, other parameters decreased after low temperature stress for short-term (2 days) as for K326 and YY85. When low-temperature stress period prolonged, these parameters come to rise gradually. As for morphological parameters, average diagram, surface area and volume of root declined significant after low-temperature stress for 2 days for YY87, while these morphological parameters are similar to normal level if prolonging stress to 6 days. However all morphological parameters are opposite for K326 comparing with YY87. Surface area, volume of root declined to some extent for YY85. These conclusion indicate different morphological and physiological ecological response mechanisms for roots of Flue-cured tobacco seedling of different variety after chilling stress. Key words: Chilling stress, flue-cured tobacco, morphology, physiology, roots.

Complex interactions between spatial pattern of resident species and invasiveness of newly arriving species affect invasibility

Understanding the factors that affect establishment success of new species in established communities requires the study of both the ability of new species to establish and community resistance. Spatial pattern of species within a community can affect plant performance by changing the outcome of inter-specific competition, and consequently community invasibility. We studied the effects of spatial pattern of resident plant communities on fitness of genotypes from the native and introduced ranges of two worldwide invasive species, Centaurea stoebe and Senecio inaequidens, during their establishment stage. We experimentally established artificial plant mixtures with 4 or 8 resident species in intra-specifically aggregated or random spatial patterns, and added seedlings of genotypes from the native and introduced ranges of the two target species. Early growth of both S. inaequidens and C. stoebe was higher in aggregated than randomly assembled mixtures. However, a species-specific interaction between invasiveness and invasibility highlighted more complex patterns. Genotypes from native and introduced ranges of S. inaequidens showed the same responses to spatial pattern. By contrast, genotypes from the introduced range of C. stoebe did not respond to spatial pattern whereas native ones did. Based on phenotypic plasticity, we argue that the two target species adopted different strategies to deal with the spatial pattern of the resident plant community. We show that effects of spatial pattern of the resident community on the fitness of establishing species may depend on the diversity of the recipient community. Our results highlight the need to consider the interaction between invasiveness and invasibility in order to increase our understanding of invasion success.

Genetic Parameters and Development of a Selection Index for Breeding Red Raspberries for Processing

New commercial red raspberry (Rubus idaeus) cultivars suited to machine-harvesting and processing markets need to be high-yielding and have good fruit quality attributes, including fruit firmness, sugar content, acidity, flavor, and health properties. Combining many traits in one genotype is a challenge for breeders, especially for traits negatively correlated with yield. Despite its potential, the use of multiple-trait selection through selection indices has had limited application in fruit breeding. In this study, we estimated variance components, heritabilities, phenotypic and genetic correlations and breeding values for total yield (TYLD), harvest span, mid-harvest day and fruit quality traits, firmness (FIRM), soluble solids (SS), acidity (ACID), total anthocyanins (TACY), and total ellagitannins (TELG) from 1008 seedling genotypes based on 85 families derived from 45 parents harvested over three seasons in Washington state. Narrow-sense heritability estimates ranged from moderately low (0.22 for TYLD) to moderately high (0.73 for SS). All traits measured had positive genetic correlations with TYLD except for ACID (–0.35) and TACY (–0.28). Genotype × year (G×Y) interaction was high for TYLD and low for fruit quality attributes FIRM, SS, ACID, TACY, and TELG, and interactions were higher between the first (2009) and second (2010) seasons than between the second (2010) and third (2011) seasons. Using economic weights and breeding values derived from multivariate analysis for TYLD, FIRM, SS, and TACY, we constructed a selection index designed to assist with multiple-trait selection for population improvement and the development of commercial raspberry cultivars.

'ASKER' AS SOURCE OF RESISTANCE TO RASPBERRY ROOT ROT

The cultivar 'Asker' (syn. 'Winklers Samling') is one source of resistance to raspberry root rot (Phytophthora rubi) in red raspberry (Rubus idaeus). Resistance to root rot in F1 seedlings with 'Asker' as mother parent was tested by inoculation with P. rubi in hydroponic culture. Disease symptoms on roots and root regeneration after inoculation showed a continuous distribution among the seedlings, with no seedling genotypes significantly exceeding the resistant control 'Asker' or being inferior to the susceptible control 'Glen Moy' in these characters.

Using Seedling and Pericarp Tissues to Determine Maternal Parentage of Dispersed Valley Oak Recruits

The spatial pattern of established seedlings yields valuable information about variation in fecundity, dispersal, and spatial structure of distributed recruits, but separating maternal and paternal contributions in monoecious species has been hampered by the "2 parent" problem. It is now possible to determine the maternal parentage of established recruits with genetic assay of maternally derived tissues of the seed or fruit, but the DNA of weathered maternal tissues often yields unreliable genotypes, reducing the practical range of such assay. We develop a mixed assay of seedling and seed (pericarp) tissues and illustrate it with distributed recruits of California valley oak (Quercus lobata Née). Detailed analysis indicates correct maternal assignment rates of canopy patch recruits of 56% (seedling assay only) versus 94% (mixed assay). For open patch recruits, maternal assignment rates were less than 50% (seedling assay only) versus 91% (mixed assay). The strategy of choice is to use seedling genotypes to identify a small set of credible parental candidates and then deploy 3-4 well-chosen pericarp/endocarp loci to reduce that list to a single obvious maternal candidate. The increase in the number of recruits available for subsequent analysis is pronounced, increasing precision and statistical power for subsequent inference.

Interactions of Fr genes and mixed-pathogen inocula in the loblolly pine-fusiform rust pathosystem

Open-pollinated loblolly pine seedlings derived from seven maternal parents were inoculated in a greenhouse with 10 different bulked inocula of the fusiform rust fungus and assessed for disease incidence. The maternal parents are heterozygous (Rr) for one or two of nine known pathotype-specific Fr genes (fusiform rust resistance genes). Progeny were genotyped to identify carriers of known R and r alleles inherited from the maternal parents. The R alleles condition resistance to specific genotypes of the fungal pathogen, while r alleles do not condition for resistance. Interactions were tested among different host genotypes and different bulked inocula. Significant differences in virulence against R genotypes were observed in the bulked inocula. Likewise, the inocula were significantly different with regard to their ability to incite disease at the family level and in r genotypes. Across the inocula, disease levels differed significantly among families. Within each family, r genotype seedlings typically exhibited higher disease rates than did R genotype seedlings. The magnitude of difference (odds ratio) between the R versus r genotypes for disease incidence within each family varied from 1 to 32 times. Significant interactions between host and pathogen genotypes were observed in four of the seven families. These greenhouse assessments using bulked inocula sources revealed wide ranges of pathogen virulence levels against the different R alleles. Barring virulence masking by unknown resistance genes, similar virulence assessments should be effective guides for the field deployment of seedlings carrying specific R alleles to regions where inocula samples show low or no corresponding virulence.

Processo infeccioso e atividade de enzimas em plântulas de macieira de genótipo resistente ou suscetível à mancha foliar de Glomerellacausada por Colletotrichum gloeosporioides

The Glomerella leaf spot (GLS) is an emerging disease and has become a major concern to Brazilian apple producers because the most widely grown cultivar, 'Gala', is highly susceptible to the disease. So, this study aimed to investigate the early stages of infectious process of C. gloeosporioides, and understand the role of peroxidase (POD) and β -1,3-glucanases (GLU) in susceptible ('Gala') and resistant ('Fuji') apple seedling genotypes. Seedlings (75 days-old) were inoculated with C. gloeosporioides and the severity of GLS was assessed at 10 days after inoculation. Conidial germination and appressoria formation of C. gloeosporioides were evaluated at 24, 48 and 72 hours after inoculation. Enzyme activity for POD and GLU were also determined at the same time interval. Seedlings of the resistant genotype did not show symptoms of GLS, whereas the susceptible genotype exhibited 11% of necrotic leaf area. The early penetration events of C. gloeosporioides were similar in both genotypes. Cultivar-specific resistance was associated with an enhanced POD activity, while GLU activity was similar in both genotypes.

Optimization of a SNP assay for genotyping Theobroma cacao under field conditions

The tropical tree crop Theobroma cacao L. is grown commercially for its beans, which are used in the production of cocoa butter and chocolate. Although the upper Amazon region is the center of origin for cacao, 70% of the world’s supply of cacao beans currently comes from small farms in West Africa. While cacao breeding programs in producer nations are the source of improved planting material, modern marker-based breeding is difficult to perform due to the lack of genotyping facilities in these countries. While DNA extraction can be routinely performed, the equipment needed to analyze simple sequence repeats (SSRs) is seldom available, forcing the outsourcing of genotyping to foreign laboratories and delaying the breeding process. We describe a 5′ nuclease (TaqMan)-based single nucleotide polymorphism (SNP) assay for genotyping cacao plants under conditions similar to those found in most cacao-producing areas. The assay was tested under field conditions by planting open pollinated seeds of seven pods from four different maternal plants. The resulting 171 seedlings were successfully genotyped with 18 SNP markers representing 12 loci. The ability to use temperature-stable reagents and rapid DNA extraction methods is also explored. Additionally, by examining the seedling genotypes for the SNP markers and 14 additional SSR markers, we investigated whether seeds in a pod are the result of single or multiple pollination events. This simple, effective method of genotyping cacao seedlings in the field should allow for more efficient resource management of seed gardens and is currently being implemented in Ghana.

Rain Damage to Strawberries Grown in Southeast Queensland: Evaluation and Genetic Control

In Queensland, Australia, strawberries (Fragaria ×ananassa Duchesne) are grown in open fields and rainfall events can damage fruit. Cultivars that are resistant to rain damage may reduce losses and lower risk for the growers. However, little is known about the genetic control of resistance and in a subtropical climate, unpredictable rainfall events hamper evaluation. Rain damage was evaluated on seedling and clonal trials of one breeding population comprising 645 seedling genotypes and 94 clones and on a second clonal population comprising 46 clones from an earlier crossing to make preliminary estimates of heritability. The incidence of field damage from rainfall and damage after laboratory soaking was evaluated to determine if this soaking method could be used to evaluate resistance to rain damage. Narrow-sense heritability of resistance to rain damage calculated for seedlings was low (0.21 ± 0.15) and not significantly different from zero; however, broad-sense heritability estimates were moderate in both seedlings (0.49 ± 0.16) and clones (0.45 ± 0.08) from the first population and similar in clones (0.56 ± 0.21) from the second population. Immersion of fruit in deionized water produced symptoms consistent with rain damage in the field. Lengthening the duration of soaking of ‘Festival’ fruit in deionized water exponentially increased the proportion of damage to fruit ranging in ripeness from immature to ripe during the first 6-h period of soaking. When eight genotypes were evaluated, the proportion of sound fruit after soaking in deionized water in the laboratory for up to 5 h was linearly related (r2 = 0.90) to the proportion of sound fruit in the field after 89 mm of rain. The proportion of sound fruit of the breeding genotype ‘2008-208’ and ‘Festival’ under soaking (0.67, 0.60) and field (0.52, 0.43) evaluations, respectively, is about the same and these genotypes may be useful sources of resistance to rain damage.

Pollen and seed dispersal inferred from seedling genotypes: the Bayesian revolution has passed here too

Understanding precisely how plants disperse their seeds and pollen in their neighbourhood is a central question for both ecologists and evolutionary biologists because seed and pollen dispersal governs both the rate of spread of an expanding population and gene flow within and among populations. The concept of a 'dispersal kernel' has become extremely popular in dispersal ecology as a tool that summarizes how dispersal distributes individuals and genes in space and at a given scale. In this issue of Molecular Ecology, the study by Moran & Clark (2011) (M&C in the following) shows how genotypic and spatial data of established seedlings can be analysed in a Bayesian framework to estimate jointly the pollen and seed dispersal kernels and finally derive a parentage analysis from a full-probability approach. This approach applied to red oak shows important dispersal of seeds (138 m on average) and pollen (178 m on average). For seeds, this estimate contrasts with previous results from inverse modelling on seed trap data (9.3 m). This research gathers several methodological advances made in recent years in two research communities and could become a cornerstone for dispersal ecology.

Purple-leaved Japanese Barberry (var. atropurpurea) Genotypes Become Visually Indistinguishable from Greenleaved Genotypes (Berberis thunbergii DC.) at Low Light Levels

Abstract Japanese barberry (Berberis thunbergii DC.) is a popular nursery plant that has escaped from cultivation to establish invasive populations across the United States. Previous studies demonstrate that green-leaved feral plants adapt successfully to low light levels. The leaf color phenotype of purple-leaved Japanese barberry (Berberis thunbergii var. atropurpurea) seedlings grown under shaded conditions was studied to determine their appearance under low light conditions typical of wooded areas often invaded by barberry. Seedlings from B. thunbergii var. atropurpurea were grown in full sunlight and under three shade treatments (36, 50 and 72%). Seedlings were also grown in full sunlight and under two higher shade treatments (85 and 95%) in a second study. The hue angle of purple seedlings increased from a mean of 22.3 in full sun to 86.9 at 72% shade, reflecting a color change from violet-purple to green-umber. Foliage color also became more vivid and lighter as shading increased. All purple genotype seedlings appeared green when grown at 95% shade due to lack of anthocyanin production at this light exposure. Escaped barberry seedlings originating from landscape plants of var. atropurpurea may not be recognized as purple-leaved forms when they invade densely shaded woodland environments.

The relationship between bitterness and drought resistance of almond (Prunus dulcis Mill.)

Cynogenesis has been suggested to be an adaptive response to drought stress in some plants. To determine the possibility of cyanogenic compounds role in almond resistance to drought stress, three different irrigation levels including moderate and severe stress (soil water potential, Ψsoil = -1.2 and -1.8 MPa, respectively) and a control treatment (Ψsoil = -0.33 MPa) were applied for five weeks to six different almond seedling genotypes including Bitter (homozygote bitter), Butte (heterozygote sweet), `Shahrood’12 (SH12), `Shahrood’18 (SH18), `Shahrood’21 (SH21) and White (all heterozygote sweet). Cyanogenic compounds including amygdalin and prunasin and the nitrogen content in the roots and shoots were measured throughout the study. Results showed that nitrogen content tend to be lower in leaves and higher in roots however; differences were not significantly different between genotypes. Severe stressed plants generally showed higher root N content although this was only significantly different for SH18, SH12 and White. There was no amygdalin in vegetative parts of plants. Bitter genotype had the highest prunasin content in its roots compared to the other genotypes. Water stress had no effect on the content of cyanogenic compounds in the leaves of all genotypes, while in roots of all genotypes except Butte and White; water stress caused a decrease in prunasin content. Hence bitterness does not play any role in drought tolerance mechanisms in almond.

The relationship between bitterness and drought resistance of almond (Prunus dulcis Mill.)

Cynogenesis has been suggested to be an adaptive response to drought stress in some plants. To determine the possibility of cyanogenic compounds role in almond resistance to drought stress, three different irrigation levels including moderate and severe stress (soil water potential, Ψsoil = -1.2 and -1.8 MPa, respectively) and a control treatment (Ψsoil = -0.33 MPa) were applied for five weeks to six different almond seedling genotypes including Bitter (homozygote bitter), Butte (heterozygote sweet), `Shahrood’12 (SH12), `Shahrood’18 (SH18), `Shahrood’21 (SH21) and White (all heterozygote sweet). Cyanogenic compounds including amygdalin and prunasin and the nitrogen content in the roots and shoots were measured throughout the study. Results showed that nitrogen content tend to be lower in leaves and higher in roots however; differences were not significantly different between genotypes. Severe stressed plants generally showed higher root N content although this was only significantly different for SH18, SH12 and White. There was no amygdalin in vegetative parts of plants. Bitter genotype had the highest prunasin content in its roots compared to the other genotypes. Water stress had no effect on the content of cyanogenic compounds in the leaves of all genotypes, while in roots of all genotypes except Butte and White; water stress caused a decrease in prunasin content. Hence bitterness does not play any role in drought tolerance mechanisms in almond.

Realized gene flow within mixed stands of Quercus robur L. and Q. petraea (Matt.) L. revealed at the stage of naturally established seedling

The estimates of contemporary gene flow assessed based on naturally established seedlings provide information much needed for understanding the abilities of forest tree populations to persist under global changes through migration and/or adaptation facilitated by gene exchange among populations. Here, we investigated pollen- and seed-mediated gene flow in two mixed-oak forest stands (consisting of Quercus robur L. and Q. petraea [Matt.] Liebl.). The gene flow parameters were estimated based on microsatellite multilocus genotypes of seedlings and adults and their spatial locations within the sample plots using models that attempt to reconstruct the genealogy of the seedling cohorts. Pollen and seed dispersal were modelled using the standard seedling neighbourhood model and a modification--the 2-component seedling neighbourhood model, with the later allowing separation of the dispersal process into local and long-distance components. The 2-component model fitted the data substantially better than the standard model and provided estimates of mean seed and pollen dispersal distances accounting for long-distance propagule dispersal. The mean distance of effective pollen dispersal was found to be 298 and 463 m, depending on the stand, while the mean distance of effective seed dispersal was only 8.8 and 15.6 m, which is consistent with wind pollination and primarily seed dispersal by gravity in Quercus. Some differences observed between the two stands could be attributed to the differences in the stand structure of the adult populations and the existing understory vegetation. Such a mixture of relatively limited seed dispersal with occasional long distance gene flow seems to be an efficient strategy for colonizing new habitats with subsequent local adaptation, while maintaining genetic diversity within populations.

MORPHOLOGICAL CHARACTERIZATION OF ELITE GENOTYPES OF GUAVA (PSIDIUM GUAJAVA L.) SEEDLINGS

High variability in tree growth and shape and horticultural performance is very common in guava (Psidium guajava L.) orchards in Zulia state, Venezuela. In consequence, morphological characterization of elite genotypes of guava seedlings was completed. Guava variants with white or red mesocarp and endocarp were chosen. The research was performed at the Centro Fruticola de Zulia, Mara County (10°48'00 LN, 71°48'00 LW), and at RFA and La Rosaida orchards, Baralt county (09°36'02 LN, 70°58'33 LW), Zulia State, Venezuela. The recorded quantitative and qualitative variables were: stem surface (SS), perimeter (PS), internode length (LI) and phyllotaxy (F), leaf shape (LS), leaf margin (ML), foliar area (AF), apex (FA) and leaf base (FB) shapes, and flowers (flower diameter (DF). Frequency tables and analysis of variance were utilized to evaluate the qualitative and quantitative variables, respectively. Multivariate analysis through principal components analysis (PCA) was accomplished to determine the typical traits of each guava variant. Regarding the qualitative variables, the acute FB, sinuate ML, opposite F and smooth with few flaky SS predominated in white and red guavas. The oblong LS and obtuse FA was present in white guavas, while elliptical LS and acute FA dominated in red guavas. The quantitative variables AF, LI and PS were significantly different (P 0.05) were determined for DF. The first three PCAs expressed 78% of the variability among guava variants. The variables that allowed differentiating guava variants were: AF, LI, FB, SS and PS.

In vitro regeneration of cocona (Solanum sessiliflorum, Solanaceae) cultivars for commercial production

Cocona (Solanum sessiliflorum Dunal) is a solanaceous shrub native to the Amazon region that produces an edible fruit. This species has numerous advantages, particularly a high nutritional value and productivity. However, due to irregular germination and rapid loss of seed viability, there are few plantations for production on a large scale. Development of alternative propagation strategies is essential for the production of homogeneous seedlings of genotypes with superior agronomic performance. We developed techniques for in vitro regeneration of the cocona varieties Santa Luzia and Thaís for large-scale production of healthy plantlets. Twenty days after seeding, seedling segments germinated in vitro were used as explant sources. Three successive experiments were performed: one to test the effect of the explant source and combinations of two growth regulators, auxin (indole acetic acid, IAA) and kinetin (KIN), on the morphogenetic response; another to investigate the effect of the combination of growth regulators on the morphogenetic response of hypocotyl segments, and another to evaluate how sucrose concentration affects the development of adventitious shoots. The best shoot induction was obtained using hypocotyl segments and stem apices, while rhizogenesis was greatest in leaves with a petiole. The number of adventitious shoots per explant on hypocotyl segments increased with 10 and 20 mg/L KIN, combined with 0.02 mg/L IAA in the variety Santa Luzia. Sucrose combined with these growth regulator levels increased the average number of calli; these were optimally produced when 45 g/L sucrose and 0.01 mg/L IAA + 20 mg/L KIN were applied. Only sucrose concentration influenced shoot proliferation in the two S. sessiliflorum varieties, with a maximum at 17.5 g/L.

Field Evaluation of 64 Rootstocks for Growth and Yield of ‘Kensington Pride’ Mango

Despite an abundance of polyembryonic genotypes and the need for rootstocks that improve scion yield and productivity, simultaneous field testing of a wide range of mango (Mangifera indica L.) genotypes as rootstocks has not previously been reported. In this experiment, we examined the growth and yield of ‘Kensington Pride’ on 64 mango genotypes of diverse origin during the first four seasons of fruit production to identify those worth longer-term assessment. We also recorded morphological characteristics of seedlings of 46 of these genotypes in an attempt to relate these measures to subsequent field performance. Tree canopy development on the most vigorous rootstocks was almost double that on the least vigorous. Growth rates differed by more than 160%. Cumulative marketable yield ranged from 36 kg/tree for the lowest yielding rootstock to 181 kg/tree for the most productive. Yield efficiency also differed markedly among the 64 rootstocks with the best treatment being 3.5 times more efficient than the poorest treatment. No relationship was found between yield efficiency and tree size, suggesting it is possible to select highly efficient rootstocks of differing vigor. Two genotypes (‘Brodie’ and ‘MYP’) stood out as providing high yield efficiency with small tree size. A further two genotypes (‘B’ and ‘Watertank’) were identified as offering high yield efficiency and large tree size and should provide high early yields at traditional tree spacing. Efforts to relate the morphology of different genotype seedlings to subsequent performance as a rootstock showed that nursery performance of mango seedlings is no indication of their likely behavior as a rootstock. The economic cost of poor yields and low yield efficiencies during the early years of commercial orchard production provide a rationale for culling many of the rootstock treatments in this experiment and concentrating future assessment on the top ≈20% of the 64 treatments. Of these, ‘MYP’, ‘B’, ‘Watertank’, ‘Manzano’, and ‘Pancho’ currently show the most promise.

SUITABILITY OF DIFFERENT VINEYARD PEACH GENOTYPES FOR GENERATIVE ROOTSTOCKS PRODUCTION

ISHS XXVII International Horticultural Congress - IHC2006: International Symposium on Seed Enhancement and Seedling Production Technology SUITABILITY OF DIFFERENT VINEYARD PEACH GENOTYPES FOR GENERATIVE ROOTSTOCKS PRODUCTION

Comparing direct vs. indirect estimates of gene flow within a population of a scattered tree species

The comparison between historical estimates of gene flow, using variance in allelic frequencies, and contemporary estimates of gene flow, using parentage assignment, is expected to provide insights into ecological and evolutionary processes at work within and among populations. Genetic variation at six microsatellite loci was used to quantify genetic structure in the insect-pollinated, animal-dispersed, low-density tree Sorbus torminalis L. Crantz, and to derive historical estimates of gene flow. The neighbourhood size and root-mean-squared dispersal distance inferred from seedling genotypes (N(b) = 70 individuals, sigma(e) = 417 m) were similar to those inferred from adult genotypes (N(b) = 114 individuals, sigma(e) = 472 m). We also used parentage analyses and a neighbourhood model approach after an evaluation of the statistical properties of this method on simulated data. From our data, we estimated even contributions of seed- and pollen-mediated dispersal to the genetic composition of established seedlings, with both fat-tailed pollen and seed dispersal kernels, and slightly higher mean distance of pollen dispersal (248 m) as compared to seed dispersal (135 m). The resulting contemporary estimate of gene dispersal distance (sigma(c) = 211 m) was approximately twofold smaller than the historical estimates. Besides different assumptions and statistical nuances of both approaches, this discrepancy is likely to reflect a recent restriction in the scale of gene flow which requires manager's attention in a context of increasing forest fragmentation.