• Exploration of flowering control in Lolium perenne L.

      Byrne, Stephen; Mur, Luis AJ; Donnisson, Iain; Guiney, Emma (Teagasc, 01/08/2009)
      Flowering or heading in Lolium perenne (perennial ryegrass) is induced by a period of vernalization, followed by long days at higher temperatures. When heading occurs there is a reduction in the feed quality of the forage and therefore extending the period of vegetative growth or eliminating heading during the growing season will improve the potential of perennial ryegrass in agriculture. Conversely, a better control of flowering time and increased heading will lead to higher seed yield for commercial producers. The aim of this project was to investigate the underlying genetic control of flowering time in perennial ryegrass. An F1 population was created by crosspollinating two lines with different heading dates and a genetic linkage map was constructed using Simple Sequence Repeat (SSR) markers. The population and genetic linkage map was then used to identify Quantitative Trait Loci (QTL) associated with heading date, spike length and spikelets per spike. A number of QTL were identified for all traits, some of which had not previously been identified in perennial ryegrass. A Suppression Subtractive Hybridization (SSH) study was also employed to identify genes differentially expressed between an extremely late flowering line and earlier flowering sibling line. Expression analysis of a number of identified genes through floral induction was performed using real time RT-PCR. This revealed a number of transcripts with expression profiles indicative of a role to play in floral induction.
    • Markers associated with heading and aftermath heading in perennial ryegrass full-sib families

      Arojju, Sai Krishna; Barth, Susanne; Milbourne, Dan; Conaghan, Patrick; Velmurugan, Janaki; Hodkinson, Trevor R; Byrne, Stephen L.; Department of Agriculture, Food and the Marine, Ireland; Teagasc Walsh Fellowship Programme; EU Marie-Sklodowska-Curie Fellowship; et al. (Biomed Central, 16/07/2016)
      Background Heading and aftermath heading are important traits in perennial ryegrass because they impact forage quality. So far, genome-wide association analyses in this major forage species have only identified a small number of genetic variants associated with heading date that overall explained little of the variation. Some possible reasons include rare alleles with large phenotypic affects, allelic heterogeneity, or insufficient marker density. We established a genome-wide association panel with multiple genotypes from multiple full-sib families. This ensured alleles were present at the frequency needed to have sufficient statistical power to identify associations. We genotyped the panel via partial genome sequencing and performed genome-wide association analyses with multi-year phenotype data collected for heading date, and aftermath heading. Results Genome wide association using a mixed linear model failed to identify any variants significantly associated with heading date or aftermath heading. Our failure to identify associations for these traits is likely due to the extremely low linkage disequilibrium we observed in this population. However, using single marker analysis within each full-sib family we could identify markers and genomic regions associated with heading and aftermath heading. Using the ryegrass genome we identified putative orthologs of key heading genes, some of which were located in regions of marker-trait associations. Conclusion Given the very low levels of LD, genome wide association studies in perennial ryegrass populations are going to require very high SNP densities. Single marker analysis within full-sibs enabled us to identify significant marker-trait associations. One of these markers anchored proximal to a putative ortholog of TFL1, homologues of which have been shown to play a key role in continuous heading of some members of the rose family, Rosaceae.