Can We Increase the Drought Tolerance of Perennial Ryegrass (Lolium perenne L.) to Preserve Grassland Ecosystem Services? A Case Study with Three Bulgarian Varieties

<i>Lolium perenne</i> L. (perennial ryegrass) has various applications, including as a high-quality forage species for livestock feed; in seed mixtures used for revegetation of eroded or degraded areas as well as for lawns due to its resistance and rapid germination; for erosion control on slopes and areas with excessive steepness; for phytoremediation of soils contaminated with potentially toxic elements due to its ability to accumulate metals in its tissues; and as a cover crop to improve soil conditions and control erosion. Accordingly, <i>L. perenne</i> provides several ecosystem services, primarily related to soil stability, agriculture, and recreation. Climate change poses challenges for <i>L. perenne</i>, particularly heat and drought stress, which can reduce its yield and alter its geographical distribution. Climate change also impacts the interactions between <i>L. perenne</i> and its environment, affecting aspects like phenology (e.g., flowering time), carbon fixation, and overall resilience. However, the species' significant genetic and endophyte-related variability may allow for adaptation. The aim of the present study was to assess the drought tolerance of three Bulgarian varieties of <i>L. perenne</i>, namely Harmoniya (diploid), Tetrany, and Tetramis (tetraploids). We performed induced drought stress under laboratory conditions and monitored its effect on plants in the early stages of growth and development. A variety-specific response was found regarding the effect of different concentrations of sucrose on seed germination, primary root and stem elongation (cm), fresh biomass accumulation (g), as well as on seedling vigor index and plant development. Field experiments and yield elements were also used to assess drought susceptibility and sensitivity to stress in a real environment. The tetraploid perennial ryegrass varieties Tetrany and Tetramis showed better germination, growth, and development in laboratory tests and had higher and more stable field productivity under both optimal and stress conditions than the diploid variety Harmoniya. Ploidy was the factor that characterize them as drought-tolerant genotypes under water-limited conditions, and its potential could be used in future breeding programs.