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Doctoral thesis2024Open access

Phenotypic and genetic diversity in wild and domesticated timothy and related Phleum species : implications for breeding

Rahimi, Yousef

Abstract

Timothy (Phleum pratense L.) is a perennial grass widely cultivated for forage production and grazing in cold temperate regions. Higher temperatures and longer growing seasons caused by climate change require new adapted timothy cultivars. To broaden the gene pool for breeding, the overall aim was to understand the phenotypic and genetic diversity in the hexaploid timothy and the related diploid species P. nodosum and the tetraploid P. alpinum. In total 246 wild and domesticated accessions of different geographical origins were evaluated as individual plants in field and greenhouse. Large diversity among species and groups of accessions was found for biomass, development and production of the different tiller types; vegetative, generative and non-flowering elongated tillers. Within timothy, no significant difference was found in biomass between wild and cultivar groups of accessions. However, cultivars showed later emergence and tillering, but reached stem elongation and heading earlier than wild accessions, showing that an overall faster development has been favored in cultivars. Timothy cultivars had a higher percentage of generative tillers than wild accessions, which had more vegetative tillers that increased with latitude of accession origin. P. nodosum cultivars produced the highest number of non-flowering elongated tillers of all accessions and species, while no such tillers were found in P. alpinum. Thirty-three of the accessions were evaluated for genetic diversity, population differentiation, and signature of selection using whole genome resequencing. The genomic analyses revealed a considerably higher number of single nucleotide polymorphisms (SNPs) in timothy and P. nodosum compared to P. alpinum. A more extensive pattern of linkage disequilibrium, a lower rate of observed heterozygosity, and a higher rate of inbreeding were also found in P. alpinum, indicative of partial or complete self-pollination in this species. In timothy and P. nodosum, low relative divergence (FST) was observed when comparing cultivars with wild accessions, indicating that there has been little genetic divergence from the wild populations due to domestication. However, the genomic pattern of FST and haplotype genome scan tests showed that some genomic regions were highly differentiated, thus indicating regions affected by positive selection. These regions are involved in crucial biological processes, exemplified by the coding genes g22404, g39371, and g35607, which play key roles in biosynthesis of structural polymers like lignin and its precursors, which affect forage nutritive value and digestibility. The identified phenotypic diversity and genomic resources can be integrated in future breeding.

Keywords

accessions; breeding; forage; grass; genetic resources; perennial; population differentiation; signature of selection

Published in

Acta Universitatis Agriculturae Sueciae
2024, number: 2024:32ISBN: 978-91-8046-328-7, eISBN: 978-91-8046-329-4Publisher: Swedish University of Agricultural Sciences

    UKÄ Subject classification

    Agricultural Science

    Publication identifier

    DOI: https://doi.org/10.54612/a.3lph5jmiu6

    Permanent link to this page (URI)

    https://res.slu.se/id/publ/128545