Selection environment impacts genetic gains for persistence in three temperate perennial forage grasses

Authors: Casler, Michael

Submitted to: Italian Journal of Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2024
Publication Date: 10/20/2024
Citation: Casler, M.D. 2024. Selection environment impacts genetic gains for persistence in three temperate perennial forage grasses. Italian Journal of Agronomy. https://doi.org/10.1016/j.ijagro.2024.100018.
DOI: https://doi.org/10.1016/j.ijagro.2024.100018

Interpretive Summary: Grasses and legumes are regularly grown in association, despite often being unbalanced or incompatible. This experiment documents five generations of selection in three perennial forage grasses, intended to improve their tolerance to frequent defoliation and shading from a companion legume. There were five different selection environments: alfalfa mixture, red clover mixture, pure grass with a three-harvest hay management, tall fescue mixture with frequent defoliation, and pure grass with frequent defoliation. Selection successfully improved persistence in both of the frequent defoliation environments. Selection also successfully improved compatibility with both legumes, as measured by persistence, grass proportion of the forage crop, and total mixture yield. There was no cross-compatibility between the frequent defoliation and the legume mixture environments – these environments led to different results. These results will be important for perennial grass breeders to focus breeding efforts more directly on the target environment: frequent defoliation of management-intensive grazing systems vs. hay production of grass-legume mixtures.

Technical Abstract: Grasses and legumes are regularly grown in association, despite often being unbalanced or incompatible. This study was intended to conduct selection for persistence in three perennial grass species that have compatibility issues with alfalfa (Medicago sativa L.) or red clover (Trifolium pratense L.) and are poorly adapted to management-intensive rotational grazing. Five cycles of selection for persistence were conducted over a 24-year period for three grass species (reed canarygrass, smooth bromegrass, and timothy) in each of five selection environments: alfalfa mixture, red clover mixture, monocultures with a three-harvest hay management, tall fescue mixture with frequent defoliation, and monocultures with frequent defoliation. Selection in the two legume mixtures led to significant increases in persistence only when evaluated in legume mixtures. Selection responses were strongest when evaluated under the same legume as in the selection environment, indicating some species specificity. Selection for persistence under frequent defoliation was successful under both conditions (monoculture and tall fescue mixture), but led to no changes when evaluated with legumes. For these three grass species, cultivar development for use in mixture with legumes or for use in management-intensive rotational grazing should be based on a selection environment that mimics, as close as possible, the target production environment.