Outcrossing in lentil (Lens culinaris) depends on cultivar, location and year, and varies within cultivars

Knowledge about the degree of outcrossing is essential for onfarm crop management and breeding schemes and for lentil (Lens esculenta Medik.) only restricted evidence was available. Three varieties were investigated in two central European locations to foster research into on farm maintenance and development of cultivars. To determine outcrossing rates, the complete dominance of ‘orange cotyledons’ over ‘yellow cotyledons’ was used as a marker. The degree of outcrossing ranged from 0.06% to 5.12%. Results were strongly influenced by cultivar, year and location. The outcrossing rate of individuals also varied within cultivars, the extremes being 0% and 22.2%. There is evidence that the degree of outcrossing can be heritable. The potential for evolutionary changes in lentil cultivars can be considerable. Growing cultivars close together or as a mixture can lead to natural or even conscious selection and local adaptation. On the other hand, spatial separation may be necessary to avoid undesirable cross‐pollination.     

Outcrossing rates of barley landraces from Syria

Diversity levels in populations of barley landraces may be influenced by varying levels of natural outcrossing caused by environmental conditions. Outcrossing was studied in 10 accessions of the barley landrace Arabi Aswad from different environments in Syria. Electrophoretic variation at two codominant isoenzymes (Est1 and Est2) in six seeds of 50 families per population were analysed and multilocus outcrossing rates calculated. Results were correlated with interpolated environmental conditions. Outcrossing was, on average, 1.7% and not significantly different from the outcrossing rate of wild barley. A significant increase of outcrossing was observed with increasing inter‐annual variation in rainfall and decreasing minimum temperatures of the coldest month.     

Genetic studies in <Emphasis Type="Italic">Centrosema pubescens</Emphasis> benth,a tropical forage legume: the mating system,genetic variability and genetic relationships between <Emphasis Type="Italic">Centrosema</Emphasis> species

In this study, we used microsatellite loci to estimate the outcrossing rate of Centrosema pubescens in open-pollinated populations of 10 progenies that each contained 20 genotypes. The multilocus outcrossing rate was 27%, which suggested a mixed mating system with a predominance of autogamy. The single locus outcrossing rate was 13%. The difference was 0.040, which indicated that only 4% of outcrossing occurs in related individuals. A paternity correlation of 14% suggests that there is a low probability of finding full sibs in the progeny. Cross-amplification of the 26 microsatellite loci available for C. pubescens was evaluated across 11 different Centrosema species. Nineteen of the 26 tested microsatellites were successfully transferable across the Centrosema species. The polymorphism information content and discriminating power evaluated had averages of 0.64 and 0.77, respectively. A total of three clusters were assembled to demonstrate the genetic relationships between Centrosema species. The transferable microsatellite loci should be useful for exploiting the genetic resources of the Centrosema species and determining the outcrossing rate, which are essential for proposing effective approaches for conservation and for establishing strategies for the selection and improvement of Centrosema spp.     

Mating system in an experimental garden composed of cassava (Manihot esculenta Crantz) ethnovarieties

Crossing patterns were investigated in an experimental garden of ethnovarieties ofManihot esculenta (Euphorbiaceae) inPiracicaba, São Paulo, Brazil. A model of evolutionary dynamics for cassava presupposes genetic recombination by means of crossing within cassava gardens as a source that amplifies genetic diversity. Quantitative analysis of mating system parameters was performed using progeny arrays assayed for eight allozyme markers. The multilocus outcrossing rate (t _m)estimate (0.915±0.04)revealed that outcrossing was prevalent, but that a low level of self-pollination also occurred. The multilocus outcrossing rate ranged from 0.69 to 1.00 among eight varieties. The high value found for the outcrossing rate indicates that the ethnovarieties studied are preferentially allogamous. Genetic recombination occurred through crossing within the cassava garden, in agreement with an assumption of the model of evolutionary dynamics for this species.     

Spontaneous outcrossing in tomato depends on cultivar and environment and varies between individual flowers

Knowledge about the degree of spontaneous outcrossing of diverse genotypes is essential for breeding programmes, maintenance breeding, and seed production. For tomato (Lycopersicon esculentum Mill.), very limited scientific evidence for genotypic differences is available and evidence from Europe is scarce. To close this knowledge gap, six cultivars were investigated in three Central European locations as part of the Organic Outdoor Tomato Project. To determine outcrossing rates, the monogenetic “cut‐leaf” trait, which is dominant over the “potato‐leaf” trait, was used as morphological marker. The observed range of outcrossing was 0.0%–5.2%. Outcrossing was significantly influenced by cultivar and environment. The outcrossing rate of individual flowers varied within cultivars ranging from 0% to 37%. The potential of newly opened flowers to accept foreign pollen varied largely with the cultivar. Genotypic differences could partly be linked to flower morphology traits. The potential for recombination between tomato genotypes is generally very low but can be a source for new variation in on‐farm management.     

New strategies for increasing heterozygosity in crops: Vicia faba mating system as a study case

Our research assesses the feasibility of using artificial selection on pre-mating floral traits to modify the mating system of faba bean (Vicia faba). This analysis considered two synthetic populations, which were derived from different genetic pools and had undergone five years of multiplication. For these populations, we identified floral and inflorescence traits that influence outcrossing per plant and examined the relative importance of these traits in governing yield. Codominant isozyme loci and the mixed-mating model were used to estimate the multilocus female outcrossing rate. A maternal half-sib design was used to evaluate the additive genetic component of floral and inflorescence traits, yield and yield components. Multiple regression was used to assess the effects of floral and inflorescence traits on outcrossing and yield and components of yield. The two populations exhibited mixing mating. Self-fertilization appears to result from the action of pollinating bees, so that its incidence could be modified by selection on floral and inflorescence traits that affect pollination. Floral and inflorescence traits affected individual differences in outcrossing unequally, with most variation being associated with the numbers of displayed flowers and inflorescences. Variation among plants in reward traits and in shape, although statistically significant, had limited and inconsistent influences on individual differences in outcrossing. Yield and its components varied strongly with aspects of floral display and, to a lesser extent, floral design, except for seed weight. Overall, our results imply that both outcrossing and yield could be enhanced by selection for plants that produce more inflorescences, each with relatively few flowers.     

Value of permanent grassland habitats as reservoirs of Festuca pratensis Huds. and Lolium multiflorum Lam. populations for breeding and conservation

European natural and semi-natural grassland form reservoirs of genetic resources containing highly adapted and variable ecotype populations of forage plants. Variation within these reservoirs is stimulated by variation in natural and anthropogenic site-related factors. Changes in agricultural practices lead to the loss of many characteristic habitats. In order to preserve resources for breeding, targeted conservation strategies for germplasm in gene banks (ex-situ) or on site (in-situ) are needed. In order to define site-related criteria for the potential of habitats to preserve valuable resources for breeding and conservation, 38 different habitats across Switzerland were selected to collect Festuca pratensis Huds. and Lolium multiflorum Lam. ecotype populations. Phenotypic variation and population differentiation of 60 single plants were evaluated in a field experiment using 16 morpho-physiological traits. For F. pratensis, ecotype populations and cultivars were clearly separated and there was a significant correlation between diversity of morphological traits and geographic location of sampling sites. For L. multiflorum no clear separation of ecotype populations and cultivars was observed suggesting gene flow from adjacent temporary leys into permanent grassland. Several ecotype populations were superior to cultivars in important traits such as early heading or resistance to winter damage, indicating the importance of natural habitats as a reservoir of genetic resources for breeding. In conclusion, maintenance of permanent grassland in contrasting environments appears to be a promising strategy for preserving valuable genetic variation of forage grasses. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Habitat and management affect genetic structure of Festuca pratensis but not Lolium multiflorum ecotype populations

Genetic diversity present in permanent grassland may be valuable for broadening gene pools in breeding programmes and for conservation of genetic resources. However, little is known about the amount of genetic diversity present at specific habitats and about site‐related factors affecting it. To identify valuable habitats, genetic diversity of 12 ecotype populations and four reference cultivars of both Festuca pratensis Huds. and Lolium multiflorum Lam. was analysed using Simple sequence repeat markers (SSR). Analysis of molecular variance revealed a larger within population variation for L. multiflorum (97.1%) than for F. pratensis (92.6%). F. pratensis ecotype populations were clearly separated from cultivars and formed three distinct subclusters according to the geographic regions they were sampled from. Differences between L. multiflorum ecotype populations and cultivars were small and no grouping of populations was observed. Thus, only F. pratensis ecotype populations were structured and habitat as well as management had a slight influence on genetic structure. This information may allow the design of individual strategies for targeted utilization of genetic resources in plant breeding programmes.     

The Effect of Cultivar and Environment on β-amylase Activity is Associated with the Change of Protein Content in Barley Grains

Eight malt barley cultivars were grown in seven locations with wide ecological differences in China for two successive years to study the cultivar and environmental variation of β‐amylase activity and its association with the change of protein content in grains. The results showed that the variation in β‐amylase activity was mainly attributable to the environment (location and year), although the effect of cultivar was also highly significant. The response of β‐amylase activity to the environment differed markedly among cultivars, reflected by large difference in coefficients of variation for the cultivars grown across diverse locations. The effect of cultivar and environment on protein content showed a pattern similar to that on β‐amylase, but the variations caused by cultivar and, in particular, environment were relatively smaller for protein content than for enzymatic activity. Regression analysis showed that there was a highly significant correlation between protein content and β‐amylase activity for all cultivars but ZAU 3. However, an obvious difference existed in the constants and regressive coefficients of the equation among cultivars, suggesting genetic differences in the effect of the changed protein content on β‐amylase activity.     

Determination of the outcrossing rate of Phaseolus vulgaris L. using seed protein markers

The outcrossing rates of four varieties of Phaseolus vulgaris in Asturias (Northern Spain) were studied using seed protein polymorphisms as genetic markers. No evidence of outcrossing was obtained, and the outcrossing rate of this species at Asturias was estimated, with a confidence of 95%, as being less than 0.74%. The usefulness of seed proteins as genetic markers for obtaining estimates of outcrossing is also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic diversity in European perennial ryegrass cultivars investigated with RAPD markers

Perennial ryegrass (Lolium perenne L.) is the most important grass species for temperate grassland agriculture. The genetic relationship and distance among cultivars is largely unknown but of great interest for breeding programmes. The objectives of this study were to (i) investigate the molecular variation and structure of population cultivars, (ii) describe the relationship among cultivars in terms of the modified Rogers’ distance, and (iii) determine the minimum sample size required for characterization of cultivars of L. perenne using random amplified polymorphic DNA (RAPD) markers. A total of 22 ryegrass cultivars, mainly of European origin, were investigated with RAPD markers. The minimum sample size required for the characterization of cultivars was about 20 individuals per population. An analysis of molecular variance (AMOVA) revealed a much larger genetic variation within cultivars (66%) than between them (34%).     

Molecular evidence of outcrossing rate variability in <Emphasis Type="Italic">Brassica napus</Emphasis>

A leafy crop of Brassica napus L. called nabicol has been grown by farmers in northwestern Spain for many years, being an important horticultural product during the winter season. A collection of landraces of a Brassica napus leafy crop called nabicol is kept at ‘Misión Biológica de Galicia’ (CSIC-Spain) which can be used to search for desirable characteristics or to produce new commercial varieties to release in the market. The assessment of the mating system of nabicol landraces is particularly important to carry on adequate breeding and genetic conservation programs. The objective of this work is to estimate the outcrossing rate in nabicol under controlled pollinator conditions using SSRs. Pairs of flowering plants taken from nabicol landrace MBG-BRS0039 were placed in separated isolation cages and bumble bees (Bombus sp.) were released for facilitating the crosses between plants. A seed sample from each plant in the cross was analyzed by SSRs that were polymorphic in the parental population. We found that the crop is partially allogamous and that there is genetic variation for the outcrossing rate among individuals. Several consequences for the maintenance and genetic improvement of the crop are discussed. The existence of genetic variability for this trait is a valuable tool that will allow us to study the genetic mechanisms underlying the mating system of this crop.     

Computer-Simulated Evaluation of the Hybrid Weakness Gene System as a Means of Preventing Genetic Contamination of Rice Cultivars

Effectivness of the hybrid-weakness caused by a complementary interaction of two dominant genes Hwc₁ and Hwc₂ to suppress the spread of the red-grain gene into ordinary white-grained rice cultivars was investigated using the Monte Carlo computer simulation method. It was shown that the weakness genes, as far as being capable of reducing the fitness of the carrier by 80 percent or more, work quite effectively to suppress the genetic contamination of white-grained cultivars due to inflow of pollen from red-grained cultivars due to inflow of pollen from red-grain gene once the gene has been incorporated in to the population in the form of red-grained progeny produced as a result of the imperfect lethality of the initial hybrid between red-and white-grained cultivars. The weakness genes have little or no effect cultivars. The weakness genes have little or no effect either, when the contamination is initiated by an inflow of seeds or seedlings from ed-grained cultivars in these situations, removal (selection)of red grained plants Is the only countermeasure to exterminate the red-grain gene. The removal of red grained plants need not be intensive if carried out continuously. The spread of the red-grain gene after initial contamination is suppressed if the red-grain gene and weakness genes are linked. The suppressing effect of the linkage, however, is not substantial when the outcrossing rate is around or smaller than 0.01 as can be assumed in most rice cultivars.     

Molecular genetic diversity within and among German ecotypes in comparison to European perennial ryegrass cultivars

Perennial ryegrass (Lolium perenne L.) is the most important grass species for temperate grassland agriculture. The level and distribution of genetic variation in gene bank ecotype collections is still largely unknown but of great interest for the planning of breeding programmes. The objectives of this study were to (i) assess the molecular variance and population structure of German ecotypes at the regional and population level, (ii) assign ecotypes to germplasm pools and (iii) compare the relationship between German ecotypes and previously‐investigated European cultivars of perennial ryegrass, A total of 22 ecotypes originating from three geographic areas in Germany. each with a sample size of 20 individual plants, were investigated with 156 polymorphic RAPD markers. Genetic distance among ecotypes ranged from 0,27 to 0.48, An analysis of molecular variance (AMOVA) revealed a much larger variation within populations (71%) than among them (29%). Ecotypes from North Germany were significantly different from those of South and Middle Germany. Thus, two distinct germplasm pools could be identified. The 22 ecotypes and 22 previously investigated cultivars shared 98% of the molecular variance.     

Allozyme variation in cultivars of Cucurbita pepo L.

Summary Cultivars of Cucurbita pepo were analyzed for their isozyme phenotypes by horizontal starch gel electrophoresis. Considerable allozymic variation was observed between cultivars, especially in the aspartate aminotransferase and malate dehydrogenase isozyme systems. Each of the five fruit types represented in the 21 cultivars tested (zucchini, pumpkin, spaghetti, acorn, scallop and yellow straightneck) could be distinguished by specific allozymes or combination of allozymes. Cultivars within a fruit type gave very similar allozyme phenotypes and often could not be distinguished on the basis of the 6 assays used. Despite the outcrossing nature of the species, allozyme polymorphism within most cultivars was low and did not seriously interfere with the analysis. Approximately half of the hybrid lines tested gave heterozygous phenotypes at one or more loci, indicating that such loci could be used to screen for the percentage of hybrid seed obtained from crosses.     

Phaseolin Diversity in the Tepary Bean, Phaseolus acutifolius A. Gray

The tepary bean (Phaseolus acutifolius A. Gray) is grown mainly in and regions of Mexico and the southwestern U.S. as a subsistence crop by small farmers. It is also a store of genetic variability for traits such as disease and pest resistance and stress tolerance to improve the common bean (P. vulgaris L.). To determine geographic patterns of variation and the influence of domestication on genetic variability, the genetic diversity of phaseolin, the major seed storage protein, was characterized among 55 wild and 8 cultivated teparies using polyacrylamide gel electrophoresis. Fifteen electrophoretic phaseolin patterns were identified among wild forms, whereas only one pattern was exhibited by cultivars. This result suggests a single domestication in this species leading to a strong reduction in diversity. An additional finding is the divergence m phaseolin types between populations east and west of the Sierra Madre Occidental mountains.     

Evaluation of floral characteristics of barley in the semi-arid climate of north Syria

Previous studies have revealed that, in areas affected by severe drought, yielding ability and stability of barley (Hordeum vulgare L.) could be improved by increasing the level of heterozygosity. One possible approach to increase the heterozygosity level is to improve the outcrossing rate. In view of that, the genetic variability and phenotypic correlation coefficients involving four floral traits related to outcrossing behaviour were investigated in 274 drought adapted barley lines from the International Center for Agricultural Research in the Dry Areas (ICARDA's) current breeding programme. A significant quantitative variation existed in anther length and width, stigma length, and anther extrusion, which indicate that selection for these traits may be effective. Anther extrusion showed weak but highly significant positive correlations with anther and stigma length. Somewhat higher positive correlations were found between anther and stigma length. The results indicate that selection for high anther extrusion and longer anthers and stigmata may increase outcrossing in cultivated barley and consequently improve yielding ability through enhanced heterozygosity.     

Fluorescence in situ hybridization polymorphism using two repetitive DNA clones in different cultivars of wheat

Twenty‐two wheat cultivars and a wheat line were analysed with two‐colour fluorescence in situ hybridization (FISH) using the pSc119.2 and pAs1 repetitive DNA clones to detect if polymorphism could be observed in the hybridization patterns of different wheat cultivars. The FISH hybridization pattern of ‘Chinese Spring’ was compared with wheat cultivars of different origins. Differences were observed in the hybridization patterns of chromosomes 4A, 5A, 1B, 2B, 3B, 5B, 6B, 7B, 1D, 2D, 3D and 4D. Although a low level of polymorphism exists in the FISH pattern of different wheat cultivars, it is possible to identify 17 pairs of chromosomes according to their hybridization patterns with these two probes. This study will help to predict the expected variation in the FISH pattern when analysing wheat genetic stocks of different origin. It is presumed that variation in hybridization patterns are caused by chromosome structural rearrangements and by differences in the amount and location of repetitive sequences in the cultivars analysed.     

Rate and inheritance of cross-fertilization in faba bean (Vicia faba L.)

Summary To assess the feasibility for synthetic varieties of Vicia faba L., 108 faba bean genotypes were screened for cross-fertilization rate in five field experiments carried out in 1989 and 1990 at Wageningen.Significant genotypic differences were observed for outcrossing rate, which ranged from 1 to 55%. These percentages, however, are thought to be not high enough for a commercially feasible production of synthetic varieties.The inheritance of cross-fertilization rate, determined by testing the F₄ generation of a cross between two inbreds, both with high outcrossing rates, appeared to be of a polygenic nature, as was indicated by the wide variation in, and the continous distribution of, the cross-fertilization rates. Among the F₄ lines tested some had a significantly higher cross-fertilization rate than the parents. However, this difference was not found when these lines were retested, indicating that possibilities for successful selection for higher outcrossing rates might be limited.     

Microsatellite (SSR) variation in a collection of Malus (apple) species and hybrids

A collection of 142 accessions of 23 Malus species, derived hybrids and cultivar accessions from the USDA-ARS Plant Genetic Resources Unit's core collection, which represents an extensive range of Malus species, was screened with a set of previously described SSR (simple sequence repeat) markers. The markers were used to determine genetic identities, estimate genetic diversity, identify genetic relationships among the accessions, and determine the utility of SSR primers developed from Malus ×domestica for making genetic assessments across the whole Malus genus. All eight primer pairs amplified multiple fragments when used in polymerase chain reactions with DNA from these accessions. High levels of variation were detected with a mean of 26.4 alleles per locus and a mean direct count heterozygosity across all eight loci equal to 0.623. The eight primer pairs used in this study unambiguously differentiated all but five pairs of accessions in this collection of 142 accessions of 23 Malus species, derived hybrids and cultivars. These SSR data were not useful in identifying genetic relationships among this diverse collection of accessions, with the majority of the accessions not clustering in ways concordant with taxonomic information and/or geographic origin. The resulting phenogram resolved only two meaningful clusters, for the taxonomically isolated Section Chloromeles and for M. fusca accessions, reflecting genetic relationships arising from geographic origin. The detection of identical accessions in the collection, which were previously considered to be unique, highlights the critical need to further bolster collections of certain Malus species. This revised version was published online in July 2006 with corrections to the Cover Date.