Genetic Dissection of Cell Wall Digestibility in Perennial Ryegrass

The energy content of perennial ryegrass (Lolium perenne)is among the highest of forage grasses but it still contains an excess of protein in relation to its energy content. Past breeding efforts to improve this balance and to increase the organic matter digestibility (OMD) have focused on the increase of the water-soluble carbohydrate (WSC) fraction. However, this was achieved at the expense of the cell wall portion (NDF), which is important for rumen functioning. We therefore focus on breeding for an improved cell wall digestibility (CWD). Higher CWD can be achieved by decreasing the lignin content or by modifying the lignin composition.

Here we present a study that considers both, phenotypic and marker-assisted selection (MAS), to improve the CWD of perennial ryegrass. Association mapping was used to correlate single-nucleotide polymorphisms (SNPs) and phenotypic variation for lignin content and several components of CWD. We show that CWD is a relevant trait for breeding and our estimates predict a potential to increase milk yields by 2% by selecting the genotypes with the highest CWD values in the studied germplasm. Six molecular markers were identified as significantly associated with CWD or with Klason lignin content. The association of one polymorphism in the LpCCR1 gene with Klason lignin content was further confirmed in pair-crosses (-15% difference in Klason lignin between both homozygous classes).

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