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Segregation distortion (SD) is the deviation of genetic segregation ratios from their expected Mendelian fraction and is a common phenomenon found in most genetic mapping studies. In this study two segregating Lolium perenne populations were used to construct two genetic maps: an ‘F2 biomass’ consisting of 360 genotypes and an ‘F1 late flowering’ sibling based population consisting of 182 genotypes. Additionally two parental maps were generated for the ‘F1 late flowering’ population. SD was detected and p-values for SD were calculated for each marker locus. The ‘F1 late flowering’ map had only half of the extent of SD (32%) compared to the map based on the ‘F2 biomass’ population (63%). Molecular marker data have been supplemented with genomic in situ hybridization (GISH) data to show non major non-recombined segments of Fescue chromosomes within the parental inbred ryegrass lines with a Festuca × Lolium pedigree. We conclude that SD in our study is more likely caused by genetic effects rather than by population structure and marker types. Two new L. perenne mapping populations including their genetic maps are introduced; one of them is the largest reported Lolium mapping population consisting of 360 individuals. [ABSTRACT FROM AUTHOR]

An expressed sequence tag (EST) library of the key grassland species perennial ryegrass ( Lolium perenne L.) has been exploited as a resource for microsatellite marker development. Out of 955 simple sequence repeat (SSR) containing ESTs, 744 were used for primer design. Primer amplification was tested in eight genotypes of L. perenne and L. multiflorum representing (grand-) parents of four mapping populations and resulted in 464 successfully amplified EST-SSRs. Three hundred and six primer pairs successfully amplified products in the mapping population VrnA derived from two of the eight genotypes included in the original screening and revealed SSR polymorphisms for 143 ESTs. Here, we report on 464 EST-derived SSR primer sequences of perennial ryegrass established in laboratory assays, providing a dedicated tool for marker assisted breeding and comparative mapping within and among forage and turf grasses. [ABSTRACT FROM AUTHOR]

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 (2 n = 4 x = 28) hybrid cultivar is used as female parent in a backcross breeding programme with L. multiflorum (2 n = 2 x = 14). A derivative of the backcross␣breeding programme was a genotype of L.␣multiflorum (2 n = 2 x = 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. [ABSTRACT FROM AUTHOR]

Synthetic varieties obtained after three to four panmictic generations are variable, not structured and so can be used for association studies. The pattern of linkage disequilibrium (LD) decay determines whether a genome scan or a candidate gene approach can be used for an association study between genotype and phenotype. Our goal was to evaluate the effect of the number of parents used to build the synthetic varieties on the pattern of LD decay. LD was investigated in the gibberelic acid insensitive gene (GAI) region in three synthetic varieties of perennial ryegrass ( Lolium perenne L.) chosen for their contrasted number of parents in the initial polycrosses. Results were compared with those obtained from a core collection. STS and SSR markers were used to evaluate variation, structuration and LD in each variety. As expected, the varieties variability increased with the number of parents almost up to the core collection variability. No structuration was observed in the varieties. Significant LDs were observed up to 1.6 Mb in a variety originated from six related parents and not above 174 kb in a variety originated from 336 parents. These results suggest that a candidate gene approach can be used when varieties have a large number of parents and a genome scan approach can be envisaged in specific regions when varieties have a low number of parents. Nevertheless, we strongly recommend to estimate the pattern of LD decay in the population and in the genomic region studied before performing an association study. [ABSTRACT FROM AUTHOR]

Ryegrass blast, also called gray leaf spot, is caused by the fungus Pyricularia sp. It is one of the most serious diseases of Italian ryegrass ( Lolium multiflorum Lam.) in Japan. We analyzed segregation of resistance in an F1 population from a cross between a resistant and a susceptible cultivar. The disease severity distribution in the F1 population suggested that resistance was controlled by a major gene ( LmPi1). Analysis of amplified fragment length polymorphisms with bulked segregant analysis identified several markers tightly linked to LmPi1. To identify other markers linked to LmPi1, we used expressed sequence tag-cleaved amplified polymorphic sequence (EST-CAPS) markers mapped in a reference population of Italian ryegrass. Of the 30 EST-CAPS markers screened, one marker, p56, flanking the LmPi1 locus was found. The restriction pattern of p56 amplification showed a unique fragment corresponding to the resistant allele at the LmPi1 locus. A linkage map constructed from the reference population showed that the LmPi1 locus was located in linkage group 5 of Italian ryegrass. Genotype results obtained from resistant and susceptible cultivars indicate that the p56 marker is useful for introduction of the LmPi1 gene into susceptible germplasm in order to develop ryegrass cultivars with enhanced resistance to ryegrass blast. [ABSTRACT FROM AUTHOR]

For ryegrass and many forage crops, characterization of varieties is often difficult for two reasons: few of discriminant morphological traits and a great within-varieties variation. Futhermore, few molecular markers are publicly accessible. In this paper we describe two approaches for the development of 42 sequence-tagged-site (STS) markers. Firstly, 14 STS markers were developed from Lolium sequences found in data bases. Secondly, 28 STS markers were developed from sequences found in related species of Gramineae. Out of 42 STS markers developed, 85.8% yielded successfull amplification and 62% revealed a high level of polymorphism with an average of five alleles per locus. The analysis of amplicons reveals a high STS marker specificity, a high conservation in gene structure and a strong intron sequence homology between allelic forms. Moreover, the majority of the STS markers can be considered as "universal markers" because 81% of these STS markers amplified successfully across 20 related grass species. These results permit us to consider the use of these markers in synteny studies. [ABSTRACT FROM AUTHOR]

Genetic structure of 120 wild populations of Lolium perenne and 50 populations of L. rigidum was studied using starch gel electrophoresis. Allelic frequencies were obtained from 12 polymorphic isozyme loci. Gene diversity indices (number of alleles (A), observed (Ho) and expected (He) heterozygosity) were significantly higher in L. rigidum (A=3.13; Ho=0.369; He=0.405) than in L. perenne (A=2.72; Ho=0.308; He=0.322). For both species, most of the diversity appeared to be within populations (GST=0.110 and 0.170 for L. perenne and L. rigidum, respectively). Despite this weak genetic differentiation, significant patterns of geographical variation for diversity indices and allele frequencies were observed in L. perenne populations; the three genetic indices (A, Ho, He) showed the same trend of variation, with the lowest values in the north-west part of the distribution area (United Kingdom, Ireland) and the highest ones in the south-east (Turkey, Lebanon, Cyprus, Iraq, Iran). In the same way, as indicated by logistic regression analyses between allelic frequencies and geographical data of L. perenne populations, the latitudinal gradient of allelic frequencies appeared to be more pronounced, although significant relationships also existed with longitude. In contrast, no spatial organization of the diversity was detected in L. rigidum. Hypotheses concerning the taxonomic relationships and the genetic and geographical origins of the two species are discussed. Lolium perenne could be derived from a small bottleneck of L. rigidum populations in the Middle East, and its present distribution area in Europe could be explained either by the extension of primitive agriculture from the fertile crescent, or as a consequence of postglacial recolonization from southern refugia. [ABSTRACT FROM AUTHOR]