Perennial ryegrass (Lolium perenne L.) is a grass species that is widely sown on dairy and sheep farms in New Zealand owing to its persistence and capacity to produce high amounts of herbage that is rich in nutrients and metabolizable energy.However, the transition from vegetative to reproductive phase results in a significant decrease in the digestibility and metabolizable energy content of ryegrass-based farm pastures, resulting in reduced animal performance, overall farm productivity, and economic gains.

To address this, past breeding efforts have aimed to delay the onset of flowering (or heading), however late heading poses certain challenges for seed production.

The main objective of this doctoral research was to explore strategies for creating a ryegrass cultivar that does not produce floral heads on farms in New Zealand and is therefore able to maintain high levels of metabolizable energy, yet can be induced to flower for seed production.

As a first step, a scalable pipeline using Oxford Nanopore long-read amplicon sequencing was developed for routine haplotype analysis in perennial ryegrass populations. This pipeline was applied to survey the key genes in the vernalization and photoperiod flowering pathways in several F2 populations generated from crosses between various New Zealand commercial cultivars and European ecotypes. These populations were found to segregate for extremely late heading (≥ +35 days) over several seasons, making it possible to compare sequence variation with flowering behaviour. Moreover, extremely late flowering plants could be induced to flower earlier by altering the duration of photoperiod (daylength), indicating extra late heading was a photoperiod duration-dependent response.

Furthermore, the use of Nanopore cDNA sequencing on the transcriptomes of mid-season and extremely late plants revealed candidate genes and pathways putatively associated with the extra late heading trait in perennial ryegrass. The discovery of gene variants in the flowering pathway contributing to extremely late flowering is the first step towards the breeding of an elite non-heading perennial ryegrass.

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Zoom link: https://otago.zoom.us/j/97756704741
Meeting ID: 977 5670 4741
Password: bioc