Abstract
Key messageExploitation of data from a ryegrass breeding program has enabled rapid development and implementation of genomic selection for sward-based biomass yield with a twofold-to-threefold increase in genetic gain.Genomic selection, which uses genome-wide sequence polymorphism data and quantitative genetics techniques to predict plant performance, has large potential for the improvement in pasture plants. Major factors influencing the accuracy of genomic selection include the size of reference populations, trait heritability values and the genetic diversity of breeding populations. Global diversity of the important forage species perennial ryegrass is high and so would require a large reference population in order to achieve moderate accuracies of genomic selection. However, diversity of germplasm within a breeding program is likely to be lower. In addition, de novo construction and characterisation of reference populations are a logistically complex process. Consequently, historical phenotypic records for seasonal biomass yield and heading date over a 18-year period within a commercial perennial ryegrass breeding program have been accessed, and target populations have been characterised with a high-density transcriptome-based genotyping-by-sequencing assay. Ability to predict observed phenotypic performance in each successive year was assessed by using all synthetic populations from previous years as a reference population. Moderate and high accuracies were achieved for the two traits, respectively, consistent with broad-sense heritability values. The present study represents the first demonstration and validation of genomic selection for seasonal biomass yield within a diverse commercial breeding program across multiple years. These results, supported by previous simulation studies, demonstrate the ability to predict sward-based phenotypic performance early in the process of individual plant selection, so shortening the breeding cycle, increasing the rate of genetic gain and allowing rapid adoption in ryegrass improvement programs.
Highlights
Perennial ryegrass (Lolium perenne L.) is the most important temperate pasture species on a global basis and plays a dominant role as the primary feed-base in dairy systems in northern Europe, Australia, New Zealand and other regions
Several aspects of ryegrass biology have contributed to this problem, such as an obligate outbreeding reproductive habit and associated high levels of genetic diversity, which have limited the fixation of desirable gene variants; a prevalence of target agronomic traits
Heritability estimates for biomass yield were calculated based on the variance components computed from the within-trial residual maximum likelihood (REML) analyses and were highly variable between trials, years and seasons, ranging from 0.05 to 0.81, with a mean of 0.42 (Online Resource 1)
Summary
Perennial ryegrass (Lolium perenne L.) is the most important temperate pasture species on a global basis and plays a dominant role as the primary feed-base in dairy systems in northern Europe, Australia, New Zealand and other regions. Several aspects of ryegrass biology have contributed to this problem, such as an obligate outbreeding reproductive habit and associated high levels of genetic diversity, which have limited the fixation of desirable gene variants; a prevalence of target agronomic traits. Ryegrasses are cultivated as genetically heterogeneous populations in a pasture sward, and agronomic performance is evaluated on a sward-specific basis. Such assessment is not appropriate for individual plants that are the target of selection in the early stages of breeding programs, which are typically grown under spaced or semispaced conditions in order to identify elite genotypes as parents for synthetic varietal production. Limited correlation has been observed between biomass yield estimates from spaced plants and corresponding sward-based performance (Wang et al 2016a, b)
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