• Capturing the economic benefit of Lolium perenne cultivar performance

      McEvoy, Mary; O'Donovan, Michael; Shalloo, Laurence; Department of Agriculture, Food and the Marine (Teagasc (Agriculture and Food Development Authority), Ireland, 2011)
      Economic values were calculated for grass traits of economic importance in Irish grass-based ruminant production systems. Traits considered were those that had the greatest potential to influence the profitability of a grazing system. These were: grass dry matter (DM) yield in spring, mid-season and autumn, grass quality (dry matter digestibility; DMD), 1st and 2nd cut silage DM yield and sward persistency. The Moorepark Dairy Systems Model was used to simulate a dairy farm. Economic values were calculated by simulating the effect of a unit change in the trait of interest while holding all other traits constant. The base scenario involved a fixed herd size and land area (40 ha), and an annual DM yield of 13 t/ha. The economic values generated under the base scenario were: € 0.152/kg for DM yield in spring, € 0.030/kg for DM yield in mid-season and € 0.103/kg for DM yield in autumn; € 0.001, € 0.008, € 0.010, € 0.009, € 0.008 and € 0.006 per 1 g/kg change in DMD for the months of April to September, respectively; € 0.03/kg for 1st cut silage DM yield, € 0.02/kg for 2nd cut silage DM yield; and − € 4.961 for a 1 percent reduction in persistency. Alternative scenarios were examined to determine the sensitivity of the economic values to changes in annual DM yield, sward utilisation and a scenario where silage production was the focus of the system. The economic values were used to calculate a total merit index for each of 20 perennial ryegrass cultivars based on production data from a 3 year plot study. The rank correlation between the merit index values for the cultivars under the base scenario and the scenario involving a reduction in herbage utilisation was 1.0, while that with the scenario involving reduced annual DM yield was 0.94. It is concluded that the total merit index can be used to identify cultivars that can generate the greatest economic contribution to a grass-based production system, regardless of system or intensity of grass production.
    • The effect of water-soluble carbohydrate concentration and type on in vitro rumen methane output of perennial ryegrass determined using a 24-hour batch-culture gas production technique

      Purcell, Peter J; Boland, T.M.; O'Kiely, Padraig; Department of Agriculture, Food and the Marine; RSF 07 517 (Teagasc (Agriculture and Food Development Authority), Ireland, 2014)
      The objective of this study was to examine the effects of water-soluble carbohydrate (WSC) concentration and type on the in vitro rumen methane (CH4) output of perennial ryegrass (PR) using a 24-hour batch-culture gas production technique. Dried and milled PR was incubated either alone (PR-O) or with added sucrose (PR-S), inulin (PR-I), or sucrose plus inulin (PR-S+I; sucrose:inulin ratio of 1:4) in sealed glass bottles [0.5 g total substrate dry matter (DM) per bottle] at 39 °C for 24 hours with buffered rumen fluid. The WSC types were added (except for PR-O) so that the WSC concentration in each fermentation bottle at the start of the incubation was either 180 (i.e., PR-O), 225, 270, 315, or 360 g/kg of total substrate DM incubated. There were linear decreases in CH4 output per gram of DM disappeared (CH4/ivDMD) and per mmol of total volatile fatty acid output (CH4/tVFA) with increasing WSC concentration in the incubated substrate. The WSC type had no effect on in vitro rumen CH4 output. It is concluded that since CH4/ivDMD and CH4/tVFA were reduced by increasing the concentration of WSC incubated with PR, it would be worthwhile to undertake in vivo experiments to examine these effects on in vivo CH4 emissions per unit of animal product.
    • Evaluation of Lolium perenne L. cv. AberDart and AberDove for silage production

      Conaghan, Patrick; O'Kiely, Padraig; Howard, H.; O'Mara, Frank P.; Halling, M.A.; European Union; Teagasc Walsh Fellowship Programme; QLK5-CT-2001-0498 (Teagasc, Oak Park, Carlow, Ireland, 2008)
      The objective of this study was to assess the value, for silage production, of intermediateheading Lolium perenne L. cultivars, AberDart and AberDove (diploid), bred for increased water-soluble carbohydrate (WSC) concentrations, relative to four control cultivars (Fennema, AberElan and Spelga (diploid), and Greengold (tetraploid)). Cultivars were evaluated for forage dry matter (DM) yield, ground cover and indirect laboratory measures of nutritional value and ensilability over 3 harvest years within intensive silage-production systems. AberDove was the most desirable diploid for silage production producing on average 316 kg/ha higher (2%) DM yield per annum, having a 10 g/kg higher (1%) dry matter digestibility (DMD) and, based primarily on a 6 g/L higher (19%) concentration of WSC expressed in the aqueous extract (WSCAE), offered the greatest potential to produce well preserved silage. Ensiling AberDart compared to the diploid controls offered a slightly greater probability of producing well preserved silage based on a modest increase of 2 g/L (6%) in WSCAE concentration. The dilemma for silage production is that AberDart, on average produced 558 kg/ha less (4%) DM yield per annum but had a greater (1%) DMD of 6 g/kg than the diploid controls. The tetraploid control had, on average, 13 and 8 g/kg higher (2% and 1%, respectively) DMD than AberDart and AberDove, but at a cost of lower ensilability with lower (6% and 21%, respectively) WSCAE values of 2 and 6 g/L. In its favour, the tetraploid control outyielded AberDart by, on average, 917 kg/ha DM per annum (7%) and produced comparable yields to AberDove. Final ground cover ratings were high (≥ 95%) for all cultivars. Evaluation of nutritional value and ensilability offers further grounds to differentiate and select cultivars for animal production potential.
    • Genomic prediction of crown rust resistance in Lolium perenne

      Arojju, Sai Krishna; Conaghan, Patrick; Barth, Susanne; Milbourne, Dan; Casler, M.D.; Hodkinson, Trevor R; Michel, Thibauld; Byrne, Stephen L.; Department of Agriculture, Food and the Marine, Ireland; Marie Sklodowska-Curie; et al. (Biomed Central, 29/05/2018)
      Background Genomic selection (GS) can accelerate genetic gains in breeding programmes by reducing the time it takes to complete a cycle of selection. Puccinia coronata f. sp lolli (crown rust) is one of the most widespread diseases of perennial ryegrass and can lead to reductions in yield, persistency and nutritional value. Here, we used a large perennial ryegrass population to assess the accuracy of using genome wide markers to predict crown rust resistance and to investigate the factors affecting predictive ability. Results Using these data, predictive ability for crown rust resistance in the complete population reached a maximum of 0.52. Much of the predictive ability resulted from the ability of markers to capture genetic relationships among families within the training set, and reducing the marker density had little impact on predictive ability. Using permutation based variable importance measure and genome wide association studies (GWAS) to identify and rank markers enabled the identification of a small subset of SNPs that could achieve predictive abilities close to those achieved using the complete marker set. Conclusion Using a GWAS to identify and rank markers enabled a small panel of markers to be identified that could achieve higher predictive ability than the same number of randomly selected markers, and predictive abilities close to those achieved with the entire marker set. This was particularly evident in a sub-population characterised by having on-average higher genome-wide linkage disequilibirum (LD). Higher predictive abilities with selected markers over random markers suggests they are in LD with QTL. Accuracy due to genetic relationships will decay rapidly over generations whereas accuracy due to LD will persist, which is advantageous for practical breeding applications.
    • 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.
    • Studies into the dynamics of perennial ryegrass (Lolium perenne L.) seed mixtures

      Gilliland, T. J.; Hennessy, Deirdre; Griffith, V. (Teagasc (Agriculture and Food Development Authority), Ireland, 2011)
      The dynamic interactions of four perennial ryegrass seed mixtures sold in Northern Ireland were studied under simulated grazing and conservation managements. Mixture composition was determined as changes in phosphoglucoisomerase isozyme frequencies by calculation from known isozyme frequencies of the component varieties. Mixture productivity was measured over 4 growing seasons and compared with yields predicted from those of the components in monoculture, weighted for their actual proportion in the mixture. No significant differences were found between actual yields for mixtures and their predicted yields, but when these differences were regressed against the heading date range among the varieties in each mixture, a significant relationship was observed. A wide range in heading date among the components of the mixtures was associated with increased yield stability over years and with a declining yield advantage for the mixture compared to its components grown as monocultures. In this aspect, the mixtures showed a more rapid decline under conservation management than under simulated grazing. Mixtures also had a flatter seasonal yield-production profile than their component varieties. Tetraploid components were more aggressive than diploids, though a more open-growing diploid maintained its proportion in the sward better than a dense-growing type and manipulating the sowing ratios could be used to influence final sward composition after 2 years. It was concluded that the differences in heading date range within mixtures had a significant impact on mixture dynamics, with the tetraploid component being the most aggressive.