Morphological variation in Dutch perennial ryegrass (Lolium perenne L.) populations,in relation to environmental factors

Summary Twenty-one Dutch Lolium perenne populations, fifteen European populations and six L. perenne cultivars were compared for morphological variation. Dutch populations clearly differed from the European populations and the cultivars. Dutch populations generally had reduced plant length and smaller leaves. For other characters, e.g. date of ear emergence, the Dutch populations showed as much variation as the European populations and cultivars they were compared with in this trial. Correlations between morphology and environmental factors at the site of origin were significant in several cases but were generally weak, and dependent on the set of populations studied. In order to maximize the phenotypic differences between the collected populations, soil type and management type appeared to be the most important factors for the choice of collection sites in the Netherlands. To determine suitable collection sites all over Europe, other factors like precipitation, latitude, altitude and temperature factors were also important. For subsampling of the locations, variation in management type within the location determined whether or not phenotypic different samples could be collected. The extensive use of cultivars in the Netherlands does not seem to have prevented the formation of distinct populations. Therefore in situ conservation of grassland seems a good alternative for genetic conservation of L. perenne in the Netherlands.Also associated with the WAU Department of Plant Taxonomy, P.O. Box 8010, 6700 ED, Wageningen, The Netherlands     

Allozyme differentiation of European populations and cultivars of Lolium perenne L., and the relation to ecogeographical factors

Summary Sixty Lolium perenne populations were screened for allozyme diversity at five loci. Objective was to determine whether allozyme diversity could be used as selection criterion for genebank accessions of L. perenne. Subsampling of locations was tested with allozyme analysis to determine whether genetically different populations could be collected at one location. Correlations between allelic frequencies and environmental factors and morphological data were established, to find ecogeographical patterns in the observed variation. Results indicated that with few examples each allelic variant could be observed in each population screened; very few unique alleles were found. Differences between populations were largely due to differences in allelic frequencies. Few correlations were found with environmental factors and morphological data. For some allele frequencies a north-south cline was observed. Generally, allozymic data of the five screened loci did not appear to be useful for the selection of accessions for genebank storage. Significant genotypic differences between populations collected at one location could be established. In general these results agreed with earlier results concerning phenotypic variation in the same populations.     

Salinity tolerant performance and genetic diversity of four rice varieties

Nuclear DNA content in 84 Hosta cultivars was measuredby flow cytometry. As an internal standard we used the closely related Agave americana, the latter was calibrated against other reference species. Propidium iodide values were 20%higher than DAPI values, indicating a lower AT/GC ratio for Hosta. Ten new tetraploid plants were found in addition to the only tetraploid known so far; H. ventricosa.Small forms of the tetraploid H. ventricosa turned out tobe triploid hybrids. Three other triploids were discovered. Threesupposed tetraploids turned out to be diploid. In five plantsthe ploidy levels of the germ layers L1 and L3 appeared to be different. In these cases thick leaves coincides with a tetraploid DNA content. The DNA contents as measured in theseploidy chimeras coincide with differences in leaf colour, thusgiving an opportunity to analyze the build-up of Hosta plants.In general, analysis of the nuclear DNA content can be used as a simple means to increase the possibilities for creating new cultivars in this economically important perennial.     

Symbiotic variability in Vicia faba. 3. Genetic effects of host plant,rhizobium strain and of host × strain interaction

Summary Six Vicia faba populations were grown in all possible combinations with six Rhizobium leguminosarum strains in order to estimate the relative importance of the three genetic components of symbiotic variability. Additive genetic effects of host genotype and rhizobium genotype accounted for only 8.9% and 11.8% of the total phenotypic variation. Non-additive variation attriabutable to specific host genotype × rhizobium genotype interactions was by far the largest component of variation and accounted for 73.8% of phenotypic differences. Therefore the greatest improvement in symbiotic nitrogen fixation is likely to arise from simultaneous selection of both symbionts.     

AFLP analysis of genetic diversity within and between populations of perennial ryegrass (Lolium perenne L.)

Amplified fragment length polymorphism (AFLP) analysis has been used to measure genetic diversity in perennial ryegrass (Lolium perenne L.) and to relate intra- and interpopulation variation to breeding history. Cluster analysis of AFLP data from contrasting populations showed features consistent with the origins of these varieties. Significant differences in intrapopulation diversity were detected and partial separation of different cultivars was observed. Restricted base cultivars, derived from small numbers of foundation clones, were suitable for this type of study, allowing near complete discrimination of closely related cultivars. Analysis of bulked samples was based on the pooling of genomic DNA from 20 individuals from 6 selected populations. Cluster analysis of AFLP data from bulked samples produced a phenogram showing relationships consistent with the results of individual analysis. AFLP profiling provides an important tool for the detection and quantification of genetic variation in perennial ryegrass. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of date of sampling and plant density upon size and digestibility of reproductive tillers of Lolium perenne L.

Summary Evaluation of forage germplasm digestibility is an important factor in screening programmes. The major problems involve the relevance of estimations made in spaced plants to plot performance, the effect of maturity, leaf: stem ratio and the choice of plant organ to be analysed. The use of stems of reproductive tiller proved successful in Lolium multiflorum. In the present experiment the effect of dates of sampling (date 1=28/6; date 2=5/7; date 3=12/7/83) and of plant densities (spaced plants and plots) on the digestibility of reproductive tillers of L. perenne cv. Marta 23 days after ear emergence was evaluated. After harvesting, the following characters were recorded on each tiller: tiller length and diameter, and spike and flag leaf length. Leaf blades and sheaths were then removed, the tillers dried and milled individually, and the in vitro digestibility assessed. The data were analysed by Analysis of Variance, Principal Components Analysis and Numerical Classification followed by a study of how the variables contributed to the derived group structure. Results: I-Plots: digestibility values were 63.4, 60.3 and 56.6% (P<0.01), respectively, for the sampling dates 1, 2 and 3. The Cramer Value (0.41) shows some correlation between tiller size and digestibility. Tillers from date 3 tend to be smaller than the others but the separation is not very clear. II-Spaced plants: digestibility values were 63.2, 60.0 and 60.8%, respectively, for dates 1, 2 and 3. Analysis of variance showed differences (P<0.01) between dates and also between genotypes. The Cramer Value (0.23) shows less correlation between tiller size and digestibility: however, tillers from dates 1 and 3 are clearly separated on the basis of size. Tillers from date 3 being smaller, date 2 tillers are located in between those from dates 1 and 3. III-Plots and single plants combined: Tillers from plots are larger than tillers from spaced plants in sampling dates 2 and 3. The Cramer Value for digestibility (0.14) is the lowest one. The results indicate differences in size and digestibility of reproductive tillers of L. perenne when contrasting situations are being compared, which suggest influence of environmental conditions upon the characters evaluated in the experiment. The differences are sufficiently high so that the use of this technique, when populations of L. perenne with wide variation in flowering dates are being evaluated, is not recommended.     

Genetic variation for disease and nematode resistances and forage quality in perennial diploid and tetraploid lucerne populations (Medicago sativa L.)

Summary Twenty-five lucerne populations of the Medicago sativa complex, which were either diploid or tetraploid and wild or cultivated, were analysed for their resistance to four different fungal diseases and to stem nematode. Forage quality, including stem digestibility and saponin content, was also tested.Populations varied in susceptibility to the diseases caused by Colletotrichum trifolii, Verticillium albo-atrum, Sclerotinia trifoliorum and Pseudopezizza medicaginis, and to the nematode Ditylenchus dipsaci. Except for Sclerotinia rot, sativa and falcata subspecies differed in susceptibility, but this grouping of populations did not account for the full range of variation among them. However, the resistance to P. medicaginis was much lower in the sativa than in the falcata populations.Populations also varied significantly in stem fiber content and digestibility. Stem digestibility was negatively correlated to forage yield. Wild sativa and falcata populations had lower fiber content and higher digestibility than cultivated sativa populations. The medicagenic acid was the sapogenin responsible for the anti-nutritional effect of the lucerne measured by the yellow mealworm larvae Tenebrio molitor. The medicagenic acid content was lowest for the pure sativa populations, highest for the pure falcata populations, and intermediate for the French sativa varieties that have some traits originating from falcata germplasm. Some populations could be used in breeding programs to improve disease and nematode resistance, and forage quality.     

Species relationships in the subgenus Ceratotropis (genus Vigna) as revealed by RAPD analysis

Summary The genetic variation among 23 accessions of 5 species in the subgenus Ceratotropis, genus Vigna, were investigated by random amplified polymorphic DNA (RAPD) analysis. A total of 404 fragments amplified with 24 primers were scored and analyzed by cluster analysis. The accessions used were separated into two main groups with an average of 70% differences. Within the main groups, five subgroups were recognized, which are in complete agreement with taxonomic species. Wild forms were always grouped with their most closely related cultivated forms and they showed variation in each species. The largest intraspecific variation was found in V. radiata (mungbean), in which wild forms (V. radiata var. sublobata) were highly different from each other and from cultivated forms. V. angularis (adzuki bean) showed the least variation and thus, was probably differentiated in relatively recent times.     

Colchicine-induced heritable variation in cell size and chloroplast number in the leaf cells of inbred ryegrasses (Lolium perenne,L. multiflorum)

Summary A 3 hr period of treatment with a 0.2% aqueous solution of colchicine was given to one week old seedlings of 3 inbred lines of perennial ryegrass (Lolium perenne) and 4 lines of Italian ryegrass (L. multiflorum). The surviving plants developed as mixoploids and were self-pollinated. In the following generation (CT1) the seeds were grown without further treatment, and were screened cytologically at the seedling stage to separate out diploids from tetraploids. Only the diploids were kept, and in this CT1 generation comparisons were then made between controls (2x) and colchicine-treated diploids (C2x) for leaf mesophyll cell size and chloroplast number variation. Heritable differences were found such that the cell plan areas and/or the numbers of chloroplasts per cell were significantly greater in the C2x compared with the 2x treatment in 3 and 5 out of the 7 lines. In each case there was enhancement of chloroplast numbers independently of the variation in cell size.     

Genetic variation in leaf epidermal cell size and shape in Lolium perenne

Summary Six diploid perennial ryegrass populations, two diploid F₁ hybrid families and the autotetraploid cv. Tove were grown in a glasshouse and the mean length and mean width of epidermal cells on the abaxial leaf surface of young fully expanded leaves compared. The diploids varied in cell length by 26%, in cell width by 9% and in length: width ratio by 39%. The cells of cv. Tove were 25% longer and 12% wider than those of the highest ranking diploid and the length: width ratio 9% higher. The DNA contents per telophase root-tip cell nucleus of a large-celled and a small-celled diploid population were similar, suggesting that the variation in epidermal cell size among diploids was due to the action of specific genes and not to differences in genome size. The mean epidermal cell dimensions of four of the above populations growing as plots in a field trial employing three levels of fertiliser nitrogen and four harvesting frequencies were measured on three occasions. Varietal ranking in cell dimensions was consistent over the different managements and dates, and agreed well with the glasshouse results. The results indicate that measurements of leaf epidermal cell length and width can be useful aids both in breeding for herbage yield and in distinguishing varieties with similar flowering dates.     

Reciprocal recurrent selection applied to Coffea canephora Pierre. I. Characterization and evaluation of breeding populations and value of intergroup hybrids

Summary Two breeding populations have been identified with Coffea canephora, based on geographical and genetic differences: the Guinean group from West Africa and the Congolese group from central Africa. A reciprocal recurrent selection programme based on these groups was initiated in Côte d'Ivoire in 1984. Genotypes of both groups available in field collections are either of cultivated or wild origin.Genotypic and phenotypic variability was evaluated within and between the groups for the following characteristics: isozyme patterns, architecture, drought tolerance and vigour, technological and organoleptic traits, pest and disease resistance. Variation between and within groups was found to be large. Based on isozyme analysis and phenotypic observations, two subgroups were identified within the Congolese group. Phenotypic values of parents and testers used in the first cycle of reciprocal recurrent selection are presented.Results of two intergroup hybrid trials indicate high yield and vigour for these hybrids compared to intragroup hybrids, justifying the reciprocal selection approach. Furthermore, the variation observed indicates that recurrent selection would allow progress for selection traits for both populations and intergroup hybrids.     

The potential for breeding an improved lucerne-rhizobium symbiosis. 1. Assessment of genetic variation

Summary Six cultivars of lucerne (Medicago sativa L.) were grown in all possible combinations with eight strains of Rhizobium meliloti in order to assess genetic variation in symbiotic nitrogen fixation. Host genotype and Rhizobium genotype effects on nitrogen fixation were respectively 4.8% and 21.0% of total phenotypic variance. Genetic variation due to host cultivar × Rhizobium strain interactions accounted for a further 6.0% of phenotypic variance. The results indicated low heritability of general symbiotic effectiveness in the host with interaction effects being large enough to suggest that plant performance may be unpredictable with populations of R. meliloti in field soils. Joint regression analysis showed that about 50% of the interactive variation could be explained by generalized differences in the sensitivity of cultivars to alterations in the genotype of Rhizobium strains. One cultivar, Siriver, was relatively insentitive to changes in the Rhizobium genotype whilst still maintaining high average yield. The implications of the results for lucerne breeding are discussed.     

Characterization of natural orchardgrass (Dactylis glomerata L.) populations of the Thrace Region of Turkey based on ploidy and DNA polymorphisms

Determining the ploidy and geneticdiversity of a germplasm is necessarybefore initiating breeding or geneticstudies. This study was conducted tocharacterize the ploidy level of 57 naturalpopulations of orchardgrass (Dactylisglomerata L.) collected from the ranges ofThrace region of Turkey and the diversityamong populations based on RAPD (RandomAmplified Polymorphic DNA) markers. Flowcytometry was used to determine nuclear DNAcontent (pg 2C^-1 = DNA content of adiploid somatic nucleus) of 6 plants foreach population. Nuclear DNA contents werecorrelated to ploidy level with root tipchromosome counts on selected plants. Onthe basis of this study, mean nuclear DNAcontent of orchardgrass was determined as9.57 ± 0.33 (with 95% confidenceinterval) while all the plants used inchromosome counting were determined to betetraploid, with 2n = 28 mitoticchromosomes, suggesting that diploidorchardgrass plants are likely very rare orabsent in ranges of Thrace region ofTurkey. In the RAPD assay, over 40polymorphic fragments were generated whichallowed some populations to bedistinguished from the rest by uniquemarkers. A cluster analysis was performedusing Nei's (1972) genetic distance indexwith an unweighted pair group method witharitmetic mean (UPGMA). The clusteranalysis indicated that there is a highlevel of gene flow among naturalorchardgrass populations and thereforegenes distributed quite homogeneouslythrough out the region. The results of thisstudy can be useful in the development ofDactylis germ plasm collectionstrategies in Thrace region for breedingpurpose.     

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%).     

Induction of novel organelle DNA variation and transfer of resistance to frost and Verticillium wilt in Solanum tuberosum through somatic hybridization with 1EBN S. commersonii

Somatic hybridization can be used to induce genetic variability in plastidial and mitochondrial genomes, and transfer multiple uncloned genes across sexual barriers. Somatic hybrids were produced between a dihaploid clone of the common potato, S. tuberosum subsp. tuberosum, and the wild sexually incongruent diploid species S. commersonii. Fusion products were selected on the basis of callus growth and regeneration in vitro. Genome composition of putative somatic hybrids was determined by flow cytometric analysis of nuclear DNA content, RAPD analysis, and Southern analysis with probes specific to organellar DNA. All regenerated fusion products proved to be hybrids based on RAPD analysis. Seventy per cent of somatic hybrids were (near) tetraploids, 22% (near) hexaploids and 8%(near) octoploids. A high correlation was found between the nuclear DNA content determined by flow cytometry and the number of chloroplasts in stomata guard cell pairs. Somatic hybrids inherited the parental plastids in a random manner. On the contrary, they preferentially inherited the mitochondrial DNA fragments of S. tuberosum. The majority of them had a rearranged mitochondrial genome with fragments from both parents. Hybrids were highly vigorous and morphologically more similar to the cultivated than to the wild parent, produced tubers on long stolons under long photoperiod conditions, showed a high degree of flowering, but did not produce pollen. In addition, somatic hybrids were generally more resistant to frost and Verticillium wilt than the cultivated parent, indicating the introgression of relevant resistance genes from the wild species into the genetic background of S. tuberosum. This revised version was published online in July 2006 with corrections to the Cover Date.     

Identification of coincident QTL for days to heading,spike length and spikelets per spike in <Emphasis Type="Italic">Lolium perenne</Emphasis> L.

Flowering time is a trait which has a major influence on the quality of forage. In addition, flowering and subsequent seed yields are important traits for seed production by grass breeders. In this study, we have identified quantitative trait loci (QTL) for flowering time and morphological traits of the flowering head in an F₁ mapping population in Lolium perenne L (perennial ryegrass), a number of which have not previously been identified in L. perenne mapping studies. QTL for days to heading (DTH) were mapped in both outdoor and glasshouse experiments, revealing three and five QTL for DTH which explained 53% and 42% of the total phenotypic variation observed, respectively. Two QTL for DTH were detected in both environments, although they had contrasting relative magnitudes in each environment. One QTL for spike length and three QTL for spikelets per spike were also identified explaining, a total of 32 and 33% of the phenotypic variance, respectively. Furthermore, the QTL for spike length and spikelets per spike generally coincided with QTL for days to heading, implying co-ordinate regulation by underlying genes. Of particular interest was a region harbouring overlapping QTL for days to heading, spike length and spikelets per spike on the top of linkage group 4, containing the major QTL for spike length identified in this population.     

Genotypical differences in nitrate content inLactuca sativa L. and related species and correlation with dry matter content

Summary Nitrate content was measured in 135 genotypes of cultivated lettuce (Lactuca sativa L.) and 21 genotypes of wildLactuca spp. grown in two experiments. In Experiment 1 plants were grown on nutrient film. In Experiment 2 plants were grown in large pots of potting soil. Within cultivated lettuce five plant types were distinguished and within each of them genotypes were found with low nitrate content. The coefficient of variation in the experiment with plants growing in large pots was not larger than in the experiment with plants growing on nutrient film. In butterhead genotypes nitrate content was negatively correlated with dry matter content and positively with plant fresh weight.     

Usefulness of the grid system in phenotypic selection for smooth bromegrass fiber concentration

Summary Grid selection was investigated as a means of reducing environmental variation prior to selection for low neutral detergent fiber (NDF) concentration in smooth bromegrass (Bromus inermis Leyss.). Eleven populations of 350 plants each were arranged into 10 grids of 35 plants each. Adjustment of NDF concentration by block means and standard deviations reduced the phenotypic variation to 50 to 94% of the original variance. Adjustment also reduced or eliminated spatial patterns of phenotypic variation in five of eight populations with significant patterns to original NDF values. Selection for low NDF tended to identify plants from blocks with a low mean NDF in some populations. When selection was based on t-scores, the number of plants representing each block was a random variable in each population. Use of grid selection with a t-score adjustment should increase the efficiency of phenotypic recurrent selection for low NDF concentration.     

Variation in vegetative parameters related to the nitrogen economy of wild barley,Hordeum spontaneum,in Israel

Summary Hordeum spontaneum, the wild progenitor of cultivated barley, has previously been examined in various studies as a germplasm resource in breeding for grain protein content and related nutritional traits.The nitrogen content and dry weight of leaf and stem (stem plus sheath) at anthesis, and the final grain size and grain protein content were measured in 33 H. spontaneum and two H. vulgare genotypes. H. spontaneum was generally higher in nitrogen content of leaves and stems, but lower in dry weight at anthesis. Consistent with previous reports, the H. spontaneum genotypes were considerably higher in grain protein than the cultivars. There was wide variation between and within populations of H. spontaneum suggesting that for breeding purposes lines combining high vegetative nitrogen content, dry weight and grain protein content can be selected.Incumbent of the Seagram Chair for Plant Science     

A genomic library of Lycopersicon pennellii in L. esculentum: A tool for fine mapping of genes

The cultivated tomato contains only a small fraction of the genetic variation present in its wild relatives. In order to use the wild germplasm in tomato breeding and genetic studies we developed a new kind of genetic resource which is composed of 50 L. esculentum lines each containing a single introgression from the green fruited species L. pennellii (LA 716). Each of the introgression lines is nearly isogenic to the cultivated tomato; these lines provide complete coverage of the wild species genome. The lines contain on the average an introgression of 33 cM from a total genome size of 1200 cM. The size and identity of the introgressed segments was determined based on RFLP analysis of 350 markers. This resource can be viewed as a genomic library of the wild species in the cultivated background. It covers the entire genome with single independent inserts per line and therefore every phenotypic difference between the introgression lines can be associated with the unique introgressed segment. The development and potential application of this resource are discussed.