Effects of Environmental Factors on Seed Germination of Italian ryegrass ( <i>Lolium perenne</i> ssp. <i>multiflorum</i> ) and Its Impact on Wheat Yield

Abstract Italian ryegrass [ Lolium perenne L. ssp. multiflorum (Lam.) Husnot] is one of the most common and malignant weeds that seriously affects wheat yield. Investigating its germination ecology and competitive dynamics with wheat is essential for predicting its potential invasion areas and developing effective management strategies. This study evaluated the effects of key environmental factors (pH, temperature, light, salinity, osmotic stress, and burial depth) on the seed germination and emergence of L. perenne ssp. multiflorum , and further quantified the impact of varying weed densities on wheat yield. The results showed that L. perenne ssp. multiflorum exhibits broad adaptability to environmental conditions. Optimal germination (70% to 86%) occurred at constant temperatures of 10 to 25 C. High germination rates (84% to 98%) were sustained across a wide pH range (4 to 10). Germination remained above 50% at osmotic potentials as low as -0.7 MPa. The germination rate of L. perenne ssp. multiflorum decreases with the increase in salt concentration, and was completely inhibited at 300 mM NaCl. Emergence was highest (92%) at 2 cm burial depth, remained above 80% from 0.5 to 6 cm, declined sharply beyond 10 cm, and was negligible at 14 cm. Field experiments demonstrated a density-dependent reduction in wheat yield by competition from L. perenne ssp. multiflorum , primarily through decreased wheat spike density and grains per spike, thereby reducing yield. Increasing wheat sowing density from 67.5 to 202.5 kg ha -1 could significantly mitigate these losses. These findings provide critical insights into the ecological adaptability of L. perenne ssp. multiflorum and its potential impact on agricultural systems, which can inform integrated weed management strategies.