Characterization of Populations of Turf-Type Perennial Ryegrass Recurrently Selected for Superior Freezing Tolerance

摘要

Perennial ryegrass (Lolium perenne L.) is an important turfgrass species used for lawns, sports fields, and recreational areas. Insufficient tolerance to subfreezing temperatures compromises its persistence in northern climates. A recurrent selection method, entirely performed indoors, was applied to two initial genetic backgrounds to generate populations putatively more tolerant to freezing (TF populations). The objective of the present study was to assess physiological and molecular responses after four cycles of selection (TF1a€“TF4). Freezing tolerance and cold-induced metabolites were monitored in plants hardened to natural variations in temperatures in fall and winter in an unheated greenhouse. Recurrent selection improved freezing tolerance expressed as the lethal temperature for 50% of the plants (LT50) and the vigor of regrowth after freezing. Significant changes in the levels of total and individual cold-induced carbohydrates (fructans) and amino acids (glutamine and proline) in crowns of hardened plants occurred in response to selection. Both groups of metabolites showed an opposite response to selection. The observation of DNA polymorphisms and progressive genetic differentiation between the initial populations and advanced cycles of selection suggests an impact of selection on allelic composition. Recurrent selection had a positive impact on freezing tolerance of perennial ryegrass through modifications in the molecular and genetic makeup of the populations.