Development and Tiller Formation in Wild and Domesticated Accessions of Timothy (Phleum pratense) and Its Relatives P. nodosum and P. alpinum

The perennial grass timothy (Phleum pratense) is an important forage crop in cold temperate regions. It forms three types of tillers: vegetative (VEG), generative (GEN), and non-flowering elongated (ELONG). To understand the influence of plant development and tiller formation on biomass production and the diversity in these traits, a total of 246 wild and domesticated accessions of timothy and the related species, P. nodosum and P. alpinum, were investigated. The length of different plant developmental stages and the formation of different tiller types were studied to test the hypotheses: (1) the proportion (%) of different tiller types affects biomass and is influenced by the lengths of the different plant developmental stages, (2) domestication and breeding have affected the length of developmental stages and proportions of tiller types. While timothy cultivars did not differ significantly from wild accessions in biomass, wild accessions had higher VEG%, which increased with latitude of accession origin. P. nodosum cultivars produced the highest number of ELONG of all accessions and species, and the ELONG% showed a strong positive correlation with biomass. Timothy cultivars showed later emergence and tillering, and reached stem elongation and heading earlier than wild accessions, suggesting that delayed tillering, but an overall faster development, has been favoured during breeding. The time between tillering and stem elongation showed a positive correlation with VEG%. This study reveals large diversity in developmental and tiller traits among accessions, reflecting differences in their domestication and breeding history, and highlighting the importance of considering early developmental traits and ELONG formation for yield and quality in further pre-breeding research.