Abstract
Perennial ryegrass is an important forage crop in dairy farming, either for grazing or haying purposes. To further optimise the forage use, this study focused on understanding forage digestibility in the two most important cuts of perennial ryegrass, the spring cut at heading and the autumn cut. In a highly diverse collection of 592 Lolium perenne genotypes, the organic matter digestibility (OMD) and underlying traits such as cell wall digestibility (NDFD) and cell wall components (cellulose, hemicellulose, and lignin) were investigated for 2 years. A high genotype × season interaction was found for OMD and NDFD, indicating differences in genetic control of these forage quality traits in spring versus autumn. OMD could be explained by both the quantity of cell wall content (NDF) and the quality of the cell wall content (NDFD). The variability in NDFD in spring was mainly explained by differences in hemicellulose. A 1% increase of the hemicellulose content in the cell wall (HC.NDF) resulted in an increase of 0.81% of NDFD. In autumn, it was mainly explained by the lignin content in the cell wall (ADL.NDF). A 0.1% decrease of ADL.NDF resulted in an increase of 0.41% of NDFD. The seasonal traits were highly heritable and showed a higher variation in autumn versus spring, indicating the potential to select for forage quality in the autumn cut. In a candidate gene association mapping approach, in which 503 genes involved in cell wall biogenesis, plant architecture, and phytohormone biosynthesis and signalling, identified significant quantitative trait loci (QTLs) which could explain from 29 to 52% of the phenotypic variance in the forage quality traits OMD and NDFD, with small effects of each marker taken individually (ranging from 1 to 7%). No identical QTLs were identified between seasons, but within a season, some QTLs were in common between digestibility traits and cell wall composition traits confirming the importance of hemicellulose concentration for spring digestibility and lignin concentration in NDF for autumn digestibility.
Highlights
Forage grasses are the main sources of energy and protein for ruminants (Fick et al, 1994)
The objective of this study was to obtain a better understanding of the variability of organic matter digestibility (OMD) in perennial ryegrass leaves harvested in spring and autumn on a wide collection of 580 genotypes
We evaluated the variance explained for OMD and neutral detergent fibre digestibility (NDFD) by the quantitative trait loci (QTL) identified for HC.Neutral Detergent Fibre (NDF)
Summary
Forage grasses are the main sources of energy and protein for ruminants (Fick et al, 1994). Breeding for high nutritive value has become one of the main objectives in forage grasses, in addition to forage yield and disease resistance (Wilkins and Humphreys, 2003; Sampoux et al, 2011). This is, in particular, the case for perennial ryegrass (Lolium perenne L.), which is one of the most used forage grass species in temperate regions thanks to its good tolerance to grazing and its overall good nutritive quality (Wong, 2005; Semae, 2020)
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