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Gray leaf spot (GLS) is a serious fungal disease caused by Magnaporthe grisea, recently reported on perennial ryegrass ( Lolium perenne L.), an important turfgrass and forage species. This fungus also causes rice blast and many other grass diseases. Rice blast is usually controlled by host resistance, but durability of resistance is a problem. Little GLS resistance has been reported in perennial ryegrass. However, greenhouse inoculations in our lab using one ryegrass isolate and one rice-infecting lab strain suggest presence of partial resistance. A high density linkage map of a three generation Italian × perennial ryegrass mapping population was used to identify quantitative trait loci (QTL) for GLS resistance. Potential QTL of varying effect were detected on four linkage groups, and resistance to the ryegrass isolate and the lab strain appeared to be controlled by different QTL. Of three potential QTL detected using the ryegrass isolate, the one with strongest effect for resistance was located on linkage group 3 of the MFB parent, explaining between 20% and 37% of the phenotypic variance depending on experiment. Another QTL was detected on linkage group 6 of the MFA parent, explaining between 5% and 10% of the phenotypic variance. The two QTL with strongest effect for resistance to the lab strain were located on linkage groups MFA 2 and MFB 4, each explaining about 10% of the phenotypic variance. Further, the QTL on linkage groups 3 and 4 appear syntenic to blast resistance loci in rice. This work will likely benefit users and growers of perennial ryegrass, by setting the stage for improvement of GLS resistance in perennial ryegrass through marker-assisted selection. [ABSTRACT FROM AUTHOR]

We describe an association mapping approach using natural populations of perennial ryegrass ( Lolium perenne L.) to identify molecular markers associated with heading date, an important trait affecting seasonal production, tillering, digestibility and grassland management regimes. Twenty-three natural populations originating from throughout Europe, with heading date phenotypes ranging from very early to very late, as well as three synthetic populations (varieties) were used for molecular marker genotyping using AFLP. In total, 589 polymorphic markers were identified. Hierarchical clustering, principal coordinate and other statistical analyses identified four outlying populations forming a clearly distinct sub-group. Removal of those four populations from the subsequent analysis reduced population sub-structure twofold. However, this made relatively little difference to the result of the association analysis. Linear regression identified three markers whose frequency of occurrence correlated with the heading date phenotype. Moreover, these markers were shown to be closely linked to each other within a major QTL on Chromosome 7, explaining 70% of the total variation in heading date. Pairwise linkage disequilibrium among them was also significant. These results suggest that association mapping approaches may be feasible in L. perenne, and that the use of natural populations could provide a useful source of genetic variation in traits of importance in crop improvement. [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]