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.     

Breeding systems in Coix lacryma-jobi populations

Summary Six populations of Coix lacryma-jobi with distinct characters were studied to evaluate the presence of autonomous apomixis and pseudogamy, and to determine its implications and effects in the calculations of the rate of breeding. For this reason, two types of genetic markers were used-morphological markers and isozymatic markers.The results show that autonomous apomixis does not seem to occur in these populations. Further experiments are necessary to prove the presence of pseudogamy in one of the populations. The rate of natural outcrossing in the grain types Rosario, Rosadlay and I-47 fluctuated around 35.9% using estimates based on isozymatic markers. The rate of natural outcrossing was 37.4% in the Adlay population using morphological markers. A population composed of tall individuals, named Tailândia, which has a greater vegetative mass and fewer grains, presented a high level of natural outcrossing at 72.8%. This information is important for many reasons, such as: 1) guiding sampling strategies of genetic material, 2) in the organization and upkeep of germplasm banks, and 3) for plant breeding programs.     

New efforts to overcome apomixis in Poa pratensis L.

Summary By means of a new method, plants of Poa pratensis can be classified rapidly and reliably as to whether they are capable or incapable of parthenogenesis. Parthenogenesis was found to be under strong genetic control, dominant over obligatory fertilization. The selected sexual plants lack all genes/alleles responsible for parthenogenesis, while the polyploid apomictic varieties investigated were heterozygous with one or more dominant alleles. Also dosage effects and/or modifying genes are probably involved. Crosses of sexual individuals with various apomictic varieties resulted in sexual as well as highly apomictic F₁ hyrids. A scheme of recurrent hybridization for breeding of Kentucky bluegrass is proposed.Two other experimental ways to overcome apomixis in Poa pratensis were studied in addition. By application of growth regulators temporary sexuality could not be induced. Attempts of in vitro regeneration of plants from endosperm resulted only in callus and root formation.     

Seasonal changes in the incidence of apomixis of diploid,triploid, and tetraploid plants of Paspalum cromyorrhizon

Summary Changes in incidence of apomixis were determined at different intervals of the flowering period in a highly sexual diploid cytotype of Paspalum cromyorrhizon Trin., a natural tetraploid cytotype of the same species, and in the triploid and tetraploid intraspecific hybrids that were produced by pollinating the 2x cytotype with pollen of the tetraploid. Reproductive behaviour was determined from observations of embryo sacs in mature ovules. Gametophytic apomixis in this species in characterized by aposporous embryo sacs which differ from normal sacs by their number, orientation inside the ovule, their dimensions and shape, and the absence of antipodal cells.The potential for apomictic reproduction increased in relation to the ploidy level, suggesting a gene dosage effect in the incidence of apomixis. In the three ploidy levels, the highest incidence of apomixis was observed when the plants reached the maximum number of flowering heads. These findings suggest that the same environmental conditions that favour flowering should also be responsible for increasing the incidence of apomixis. An additional experiment under controlled conditions indicated that the light regime should be one of the factors that govern the amount of apomictic reproduction. Thus, polyploidy and apomixis should be of special significance in the dispersion and evolution of this grass species. The 4x facultative apomictic cytotype is far more frequent in nature than the highly sexual 2x. Moreover, most of the seeds produced in a flowering season should arise asexually. So, apomixis rapidly increases the number of plants bearing the successful maternal genotype, and sexual reproduction becomes important in adverse environmental conditions.     

Novel genotypes of the subtropical grass Eragrostis curvula for the study of apomixis (diplospory)

The aim of this work was to obtain a series of genetically related lines of Eragrostis curvula with different ploidy levels and reproductive modes, which can be used for the discovery of genes associated to diplospory. E. curvula is a widely cultivated forage grass native to Southern Africa that reproduces naturally by obligate diplosporous apomixis (asexual reproduction by seeds) of the Antennaria type. In vitro culture of immature inflorescences of the apomictic cultivar Tanganyika led to the regeneration of a diploid plant with a particular morphology (plant UNST1122). Embryo sac analysis and progeny tests determined that plant UNST1122 reproduces by sexuality. UNST1122 was cloned by dividing its tillers and a R ₁ generation was obtained from seeds after open pollination among the diploid clones. A set of 500 seeds from a diploid R ₁ plant was treated with colchicine and two plants showing a duplicated chromosome number (2n = 4x = 40) were obtained (plants UNST1112 and UNST1131). Progeny tests using RAPDs indicated that these plants reproduce also by sexuality. The availability of sexual tetraploid genotypes of E. curvula will allow the production of hybrids with new interesting combinations of agronomic traits and the developing of mapping populations segregating for diplospory. Besides, these genetically related plants with different reproduction modes constitutes an excellent model for the identification of gen(es) involved in diplosporous apomixis by mRNA profiling as well as to study the genomic rearrangements and gene expression alterations associated to changes at ploidy levels.     

Interspecific crosses as a tool in breeding Poapratensis L. 1. Poalongifolia Trin × P. pratensis L.

Summary By crossing amphimictic P. longifolia and apomictic P. pratensis fertile hybrids were obtained. In F₂ populations a vast range of types was observed. New combinations were found, which is shown by data on plant length and hairiness of the lemma. Crossing F₁ hybrids with P. pratensis gave more P. pratensis-like plants. Data on seed yield, uniformity and turf performance in later generations are given. The implications for breeding are discussed and it is concluded that interspecific crosses can be used for introducing a sexual phase in P. pratensis breeding. Non-hairiness of the lemma can be incorporated.     

Meiotic behavior in Brachiaria humidicola (Poaceae) hybrids

In the genus Brachiaria, genetic variation can be exploited directly from germplasm collections or released using sexual reproduction in normally apomictic polyploids. The discovery of a natural sexual polyploid accession H031 of Brachiaria humidicola collected in Africa, opened new opportunities to exploit the genetic variation in this species. This accession was crossed with an apomictic cultivar BRS Tupi with the same chromosome number (2n = 36) and 361 F₁ hybrids were obtained. Following visual selection for leafiness, vigor, growth habit, and the mode of reproduction, 50 hybrids were selected for further agronomic evaluation. The parents and 45 of the 50 selected hybrids were evaluated for the regularity of meiosis. In the female parent (H031), meiosis was somewhat irregular, with 16.3% of abnormal tetrads, whereas the male (cv. BRS Tupi) meiosis was very regular, with only 3.1% of abnormal tetrads. Among hybrids (sexual and apomictic), the percentage of abnormal tetrads ranged from 15.8 to 98.3%. The abnormalities included irregular chromosome segregation, chromosome stickiness and the absence of cytokinesis. Considering that apomixis in the genus Brachiaria is pseudogamic, and that meiotic aberrations can compromise pollen viability, the results of this study present another parameter to aid selection for more stable microsporogenesis. Apomictic derivatives with stable meiosis are candidates for new cultivars whereas sexual hybrids can be retained in breeding for another round of recombination.     

Genetic diversity among tea cultivars from China, Japan and Kenya revealed by ISSR markers and its implication for parental selection in tea breeding programmes

Tea plant [Camellia sinensis (L.) O. Kuntze] is an important beverage crop in the world. In recent years many clonal tea cultivars have been released, and they play major roles in improving the production and quality of tea. It is important to understand the genetic diversity and relatedness of these cultivars to avoid inbreeding and narrow genetic basis in future tea breeding. In the present study, genetic diversity and relationship of 48 tea cultivars from China, Japan and Kenya were evaluated by inter‐simple sequence repeat (ISSR) markers. A total of 382 ISSR bands were scored, of which 381 (99.7%) were polymorphic. The ISSR primers showed high ability to distinguish between tea cultivars according to their high Resolving Power (R_P) with an average of 7.4. The mean of Nei’s gene diversity (H) and Shannon’s information index (I) were 0.22 and 0.35, respectively. More abundant diversity was revealed among cultivars in China than those in Japan and Kenya. Within Chinese populations, the level of diversity in east China was higher than that in other regions. The coefficient of genetic differentiation (G_ST) was 0.202, which indicates a high degree of genetic variation within populations. This result was further confirmed by analysis of molecular variance, which revealed the variance component within the populations (92.07%) was obviously larger than that among populations (7.93%). The level of gene flow (N_m) was estimated to be 2.0. This could be explained by frequent natural cross‐pollination and seed dispersal among tea populations. The pairwise similarity coefficient between the cultivars varied from 0.162 to 0.538. A dendrogram of 48 tea cultivars was constructed where all the tested cultivars were divided into two groups. Our data show that the genetic relationship among tea cultivars can be determined by the ISSR markers. This will provide valuable information to assist parental selection in current and future tea breeding programmes.     

The role of selection on the genetic structure of pathogen populations: Evidence from field experiments with Mycosphaerella graminicola on wheat

Summary Coevolution refers to reciprocal genetic changes that occur in two or more ecologically interacting species. In agricultural ecosystems, we are especially concerned with the genetic response of pathogen populations to resistant cultivars produced by plant breeding programs. It would be useful to be able to predict whether disease resistance is likely to be durable or ephemeral before a cultivar is widely grown. Though it may not be possible to predict durability in advance, knowledge of the genetic structure of pathogen populations may prove useful for making predictions about the rate at which pathogens adapt to resistant varieties. Much has been learned about the genetic structure of populations of obligate fungal pathogens such as rusts and mildews, which have become paradigms for plant pathology. We have focused our effort on the population genetics of the less known, non-specialized, necrotrophic pathogens, such as the Septorias of small grains. Our approach has been to use DNA fingerprinting and RFLP analysis to conduct field experiments that elucidate how populations of fungal pathogens adapt in agroecosystems. Our results suggest that mating system may have a greater impact than natural selection on the genetic structure of populations of Mycosphaerella graminicola (anamorph Septoria tritici).     

A test for obligate apomixis in grain sorghum R473

Summary Segregation patterns in progeny arrays of selfed plants, heterozygous for the Mdh 1 isozyme marker locus, were used in an attempt to confirm the presence of apomixis in the grain sorghum line R473. No evidence for obligate apomictic reproduction was obtained. However, our studies did not rule out the possibility of a low level of facultative apomixis in R473.     

Comparative genetic analysis of field resistance to downy mildew in the lettuce cultivars ‘Grand Rapids’ and ‘Iceberg’

Downy mildew on lettuce is currently controlled using host resistance genes (Dm genes) that confer race-specific resistance in seedlings. Field resistance (FR) that is active in adult plants but not seedlings was identified in the cvs. Grand Rapids and Iceberg. The goal of our study was to evaluate the utility of Grand Rapids as a source of novel Bremia resistance alleles, particularly in comparison with Iceberg. To measure FR, downy mildew symptoms were evaluated following natural infection in field experiments. The responses of Grand Rapids and Iceberg were similar in many respects. Although both cultivars had a small percentage of plants exhibiting disease symptoms, the average disease ratings were as low as for cultivars with effective Dm genes. We observed no evidence for race specificity. FR was effective over 3 years of our study, despite documented variation within pathogen populations. Both cultivars lacked all known seedling resistance genes except Dm13, which was not responsible for the resistance observed in field experiments. Similar segregation of FR was observed in F₂ populations for both Grand Rapids and Iceberg. The presence of highly susceptible families within Grand Rapids × Iceberg populations suggested the presence of at least one unique resistance allele in each cultivar. Preliminary genetic analysis of FR from Grand Rapids revealed a high estimate of narrow-sense heritability that suggested simple inheritance, but single gene models did not fit the observed data. Our results suggest that Grand Rapids may represent an underutilized resource for controlling downy mildew in lettuce.     

Androgenesis as a means of dissecting complex genetic and physiological controls: selecting useful gene combinations for breeding freezing tolerant grasses

The advantages of androgenesis from Lolium × Festuca hybrids as a means towards enhanced gene expression and capture of rare genetic variation are reviewed. New evidence is presented for the technique’s use in combination with introgression-mapping for targeting Festuca-derived genes for enhanced freezing-tolerance. As a starting point, a dihaploid genotype derived by androgenesis from a Lolium multiflorum × Festuca pratensis amphiploid (2n = 4x = 28) hybrid cultivar is used as female parent in a backcross breeding programme with L. multiflorum (2n = 2x = 14). A derivative of the backcross␣breeding programme was a genotype of L.␣multiflorum (2n = 2x = 14) incorporating a F.␣pratensis introgression on chromosome 4 that was more freezing-tolerant than Lolium. New evidence of the importance in Lolium and Festuca species of the adaptive capabilities of Photosystem II (PSII) in relation to subsequent freezing-tolerance, is presented. Non-photochemical quenching (NPQ) mechanisms for expulsion of excess light energy during cold acclimation are found in F. pratensis but not in L. multiflorum. Screens of a backcross population derived from an initial dihaploid genotype (n + n = 14) produced by androgenesis from a L. multiflorum × F.␣pratensis amphiploid, indicate a direct relationship between cold acclimation induced increases in NPQ and freezing-tolerance. Preliminary evidence of a role for genes found on chromosome 4 of F. pratensis for increased NPQ expression, is presented.     

Correlation of isoenzyme polymorphism and Bayoud-disease resistance in date palm cultivars and progeny

Summary Seedlings of date palm (Phoenix dactylifera L.), obtained from seven cultivars crossed with two males, were analyzed by polyacrylamide gel electrophoresis for esterase (EST), glutamate oxaloacetate transaminase (GOT), endopeptidase (ENP) and alcohol dehydrogenase (ADH) polymorphisms. Eleven, eight, five and two phenotypes were revealed for the enzymes tested, respectively. Seedlings of F₁ populations derived from Bayoud (Fusarium)-resistant and low fruit quality cultivars were characterized by a high electrophoretic polymorphism, when compared with progenies of Bayoud-susceptible and high fruit quality cultivars. In almost all cases, the most frequent electrophoretic phenotypes scored for each enzyme in different F₁ populations, were similar to those of the corresponding parent cultivars. Heterozygous phenotypes have been found for, at least, 3 loci; Got-2, Est-1 and Enp, indicating that such loci could be used to screen for hybrid seedlings. The expected Mendelian segregation of allozymes has been observed for these 3 loci, in many F₁ populations. It seems that progenies of Bayoud-resistant cultivars are characterized by a high level of electrophoretic polymorphism. The estimation of this index and the search for genetic linkage with segregating allozymes, may be biochemical criteria useful as an aid in distinguishing date palm seedling populations derived from Bayoud-resistant cultivars and suitable for breeding programs.     

Genetic diversity of feral alfalfa (<Emphasis Type="Italic">Medicago</Emphasis> <Emphasis Type="Italic">sativa</Emphasis> L.) populations occurring in Manitoba,Canada and comparison with alfalfa cultivars: an analysis using SSR markers and phenotypic traits

Feral populations of cultivated crops may act as reservoirs for novel traits and aid in trait movement across the landscape. Knowledge on the genetic diversity of feral populations may provide new insights into their origin and evolution and may help in the design of efficient novel trait confinement protocols. In this study, the genetic diversity of 12 feral alfalfa (Medicago sativa) populations originating from southern Manitoba (Canada) and 10 alfalfa cultivars and a M. falcata germplasm were investigated using eight SSR markers (i.e., microsatellites) and 14 phenotypic traits. We found that the genetic diversity observed in feral populations was similar to the diversity detected among the 10 cultivars. Analysis of molecular variance revealed that there was great genetic variation within (99.8%) rather than between different feral populations. Cluster analysis (unweighted pair-group method using arithmetic average) revealed no differentiation between feral populations and cultivars for neutral loci. High levels of population differentiation for phenotypic traits (and not for neutral markers) suggest the occurrence of heterogeneous selection for adaptive traits. The phenotypic traits we studied did not distinctly separate feral populations from cultivars but there was evidence of natural selection in feral populations for traits including winter survivability, rhizome production, and prostrate growth habit. Our results suggest that feral alfalfa populations need to be considered in the risk assessment of alfalfa containing novel genetically modified (GM) traits. Further, feral alfalfa populations may be regarded as a source of new germplasm for plant improvement.     

Genetic basis of the evolution of adaptedness in plants

Summary Adaptedness is both complexly inherited and much affected by environment: consequently the genetic mechanisms that have led to improvements in adaptedness have been difficult to identify and to quantify. Recently it has been shown that marker assisted dissection of adaptedness based on changes in the frequencies of discretely inherited alleles of loci of various kinds (e.g. allozyme, restriction fragment, microsatellite loci) is practicable. I will illustrate marker assisted analysis of the genetic basis of adaptedness with a sample of allozyme data from three species groups, two heavily selfing groups (two wild Avena species and barley) and one outcrossing species (corn, maize). The results lead to three main conclusions: (1) that the single most important genetic mechanism in all three species groups was the assembly of favorable epistatic combinations of alleles of different loci by means of recurring cycles of selection, intercrossing superior selects, and inbreeding to near homozygosity leading to stable superior multilocus genotypes adapted to specific habitats; (2) that exploitation of favorable interactions among alleles of the same locus played a significant role in tetraploid A. barbata and probably also in single-cross maize hybrids; (3) that purifying selection (elimination of deleterious alleles) played a small role in all three species groups. These results indicate that marker alleles provide applied breeders with effective ways to identify, track, and incorporate regions of chromosomes with favorable effects of adaptedness into improved cultivars.     

Inheritance of resistance in soybean PI 567516C to LY1 nematode population infecting cv. Hartwig

Worldwide, cyst nematode (SCN) Heterodera glycines is the most destructive pathogen on cultivated soybean (Glycine max (L.) Merr.). In the USA yield losses in 2001 were estimated to be nearly 60 million dollars. Crop losses are primarily reduced by the use of resistant cultivars. Nematode populations are variable and have adapted to reproduce on resistant cultivars overtime because resistance primarily traces to two soybean accessions. Recently cv. Hartwig was released which has comprehensive resistance to most SCN populations. A virulent nematode population LY1 was recently selected for its reproduction on Hartwig. LY1 population originated from a mass mating of Race 2 (HG Type 1.2.5-) females with Race 5 (HG Type 1.2-) males. LY1 nematode population infects currently known sources of resistance except PI 567516C. The female indices obtained on PI 567516C and Hartwig were 7% (resistant) and 155% (susceptible), respectively. However, the genetic basis of LY1 resistance in soybean PI 567516C is not known. Resistant PI line 567516C was crossed to susceptible cultivar Hartwig to generate 105 F_2:5 families. These families together with parents, seven indicator lines and a susceptible control cv. Lee-74 were evaluated for response to LY1 nematode population in the greenhouse. Chi-square analysis showed resistance in PI567516C to LY1 was conditioned by one dominant and two recessive genes (Rhg, rhg, rhg). Chi-square value was 0.15 and P = 0.70. This information will be useful to soybean researchers for developing resistant cultivars to nematode population that infects Hartwig.     

Race specific resistance against Phytophthora infestans in potato is controlled by more genetic factors than only R-genes

Summary For RFLP mapping of R-genes, determining resistance to specific races of Phytophthora infestans in tetraploid potato, it is necessary to develop well segregating populations at the 2x level. During mapping studies, evidence was obtained that more genetic factor(s) are involved in the expression of R-genes than conventionally believed. Two experiments are described in which such an additional genetic factor was suppressing or enhancing the expression of unknown R _nand R _ifactors. R _nand R _iappeared to be present in the investigated plant material, containing R4 and R10, or in one of the susceptible crossing parents. In a third experiment, the expression and the segregation of the well known R1 gene was influenced by an additional genetic factor. In that case there were indications for a dominant suppressor. This was established by the selection of susceptible plants carrying a RFLP allele of probe GP21 closely linked to R1. In three of the four F₁ populations, resulting from crosses between such susceptible plants and susceptible tester plants, resistnat progenies were found. The resistance appeared to be R1-specific. This clearly indicates that in three of the four investigated susceptible plants, the R1 gene was still present but not expressed.     

Regional phenotypic diversity of Puccinia triticina and wheat host resistance in western Europe, 1995

Pathogenicity data from surveys of Puccinia triticina (formerly P. recondita f. sp. tritici) conducted in western Europe in 1995 were analysed to compare the structure of regional populations of the pathogen. Many of the populations differed in phenotypic diversity and pathotypic composition, even though they occurred within a single epidemiological unit, suggesting that local factors may influence the establishment and propagation of individual pathotypes in the regional populations. Neighbouring regions were more similar than distant regions, and all regions shared at least one pathotype, except populations in northern Italy and Scotland. A high degree of similarity was found between populations in northern France and Great Britain, providing strong evidence of free movement of inoculum between these regions. Resistance genes were postulated for a selection of 91 wheat cultivars, representing those most commonly grown in western Europe in 1995. Thirteen cultivars lacked detectable seedling resistance genes and the remaining 78 possessed from one to three resistance genes; those detected were Lr1, Lr3a, Lr10, Lr13, Lr14a, Lr17b, Lr20, Lr26 and Lr37. The most commonly detected resistance gene was Lr13, which was present singly or in combination with other resistance genes in 48 cultivars (53%). The gene Lr14a was detected in 18 cultivars, Lr26 was present in 16 cultivars. The role of host selection in the composition of the regional populations of P. triticina in western Europe in 1995 was difficult to assess on the basis of the results obtained, since virulence data were not available for Lr13 and Lr14a. This revised version was published online in August 2006 with corrections to the Cover Date.     

Assessment of the degree of genetic variation in beet based on RFLP analysis and the taxonomy of Beta

Summary Clones derived from Beta vulgaris and Beta maritima were assayed for their ability to detect restriction fragment length polymorphisms (RFLPs) in different beet accessions. The clones able to detect polymorphism were used as genetic markers to assess the degree of genetic variation existing between and within different species of the genus Beta. The data support the current taxonomy of the Beta vulgaris section, while the great genetic similarity found between Beta webbiana and Beta procumbens indicates that they could belong to the same species.Enough variation was found between Beta vulgaris cultivars, allowing the isolation of a sufficient number of genetic markers for the construction of detailed genetic maps.