Contents Summary 9 Background 10 Objectives, breeding methodologies and progress in grass breeding 12 Markers and their suitability for genetic analysis in grasses 13 Associating markers to genes for ‘sustainability’ in the grasses 13 The genetic control of flowering time 16 Target traits: resilience against climate change and resistance to abiotic stresses 17 Target traits: carbohydrates and sustainable ruminant animal production 19 Target traits: grass biomass, climate change and energy sustainability 21 Conclusions 21 References 22 Summary Here, we review the current genetic approaches for grass improvement and their potential for the enhanced breeding of new varieties appropriate for a sustainable agriculture in a changing global climate. These generally out‐breeding, perennial, self‐incompatible species present unique challenges and opportunities for genetic analysis. We emphasise their distinctiveness from model species and from the in‐breeding, annual cereals. We describe the modern genetic approaches appropriate for their analysis, including association mapping. Sustainability traits discussed here include stress resistance (drought, cold and pathogeneses) and favourable agronomic characters (nutrient use efficiency, carbohydrate content, fatty acid content, winter survival, flowering time and biomass yield). Global warming will predictably affect temperature‐sensitive traits such as vernalisation, and these traits are under investigation. Grass biomass utilisation for carbon‐neutral energy generation may contribute to reduced atmospheric carbon emissions. Because the wider potential outcomes of climate change are unpredictable, breeders must be reactive to events and have a range of well‐characterised germplasm available for new applications.

Procedures for the transfer of genes for drought resistance from Festuca glaucescens (2n=4x=28) into Lolium multiflorum (2n=2x=14) are described. Following the initial hybridisation of a synthetic autotetraploid of L. multiflorum (2n=4x=28) with F. glaucescens, the F1 hybrid was backcrossed twice onto diploid L. multiflorum (2n=2x=14) to produce a diploid Lolium genotype with a single F. glaucescens introgression located distally on the nucleolar organiser region arm of chromosome 3. The transmission of F. glaucescens-derived amplified fragment length polymorphisms and a sequence-tagged-site (STS) marker was monitored throughout the breeding programme. Those genotypes of a mapping population of backcross 3 that survived combined severe drought and heat stress all contained the F. glaucescens-derived markers. The STS marker provided a prototype for a PCR-based system for high-throughput screening during cultivar development for the presence of the F. glaucescens-derived genes for drought resistance. The frequency of intergeneric recombination between L. multiflorum and F. glaucescens is described. During the initial stages of the breeding programme, preferential intraspecific chromosome pairing between Lolium homologues and Festuca homoeologues dominated with low frequencies of intergeneric chromosome associations. However, these increased in the backcross 1 due to the absence of opportunities for intraspecific chromosome pairing between homoeologous Festuca chromosomes following the loss of half of the Festuca chromosomes. Once transferred to Lolium, F. glaucescens sequences recombined with Lolium at high frequencies, thereby enabling the loss of potentially deleterious gene combinations that might reduce the forage quality of Lolium.

We describe a candidate gene approach for associating SNPs with variation in flowering time and watersoluble carbohydrate (WSC) content and other quality traits in the temperate forage grass species Lolium perenne. Three analysis methods were used, which took the significant population structure into account. First, a linear mixed model was used enabling a structured association analysis to be incorporated with the nine populations identified in the structure analysis as random variables. Second, a within-population analysis of variance was performed. Third, a tree-scanning method was used, in which haplotype trees were associated with phenotypes on the basis of inferred haplotypes. Analysis of variance within populations identified several associations between WSC, nitrogen (N), and dry matter digestibility with allelic variants within an alkaline invertase candidate gene LpcAI. These associations were only detected in material harvested in one of the two years. By contrast, consistent associations between the L. perenne homolog (LpHD1) of the rice photoperiod control gene HD1 and flowering time were identified. One SNP, in the immediate upstream region of the LpHD1 coding sequence (C-4443-A), was significant in the linear mixed model. Within-population analysis of variance and tree-scanning analysis confirmed and extended this result to the 2118 polymorphisms in some of the populations. The merits of the tree-scanning method are compared to the single SNP analysis. The potential usefulness of the 4443 SNP in marker-assisted selection is currently being evaluated in test crosses of genotypes from this work with turf-grass varieties.

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