Browsing Grassland Science by Author "Velmurugan, Janaki"
Markers associated with heading and aftermath heading in perennial ryegrass full-sib familiesArojju, 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.
Using variable importance measures to identify a small set of SNPs to predict heading date in perennial ryegrass.Byrne, Stephen; Conaghan, Patrick; Barth, Susanne; Arojju, Sai Krishna; Casler, Michael; Michel, Thibauld; Velmurugan, Janaki; Milbourne, Dan; E.U. Marie Skłodowska-Curie Fellowship; Teagasc Walsh Fellowship Programme; et al. (Nature, 2017-06-15)Prior knowledge on heading date enables the selection of parents of synthetic cultivars that are well matched with respect to time of heading, which is essential to ensure plants put together will cross pollinate. Heading date of individual plants can be determined via direct phenotyping, which has a time and labour cost. It can also be inferred from family means, although the spread in days to heading within families demands roguing in first generation synthetics. Another option is to predict heading date from molecular markers. In this study we used a large training population consisting of individual plants to develop equations to predict heading date from marker genotypes. Using permutation-based variable selection measures we reduced the marker set from 217,563 to 50 without impacting the predictive ability. Opportunities exist to develop a cheap assay to sequence a small number of regions in linkage disequilibrium with heading date QTL in thousands of samples. Simultaneous use of these markers in non-linkage based marker-assisted selection approaches, such as paternity testing, should enhance the utility of such an approach.