Seed germination behavior of glyphosate-resistant and susceptible Italian ryegrass (Lolium multiflorum Lam.)

Ryegrass (Lolium multiflorum Lam.) is one of the most difficult annual weeds to control in cultivation systems worldwide, especially in temperate regions. The widespread use of herbicides in the past two decades has selected resistant biotypes of ryegrass in crops in Southern Brazil. Ryegrass seeds are dormant when disseminated and germination can be staggered over time (crop-growing season). Knowledge of the germination behavior of seeds from herbicide-resistant plants has been little studied, but it would be very useful in integrated weed management. Thus, this study aimed to characterize the dynamics of the soil seed bank of two biotypes of L. multiflorum, one glyphosate-resistant and the other glyphosate-susceptible, under a no-tillage system. The treatments were arranged in a bifactorial scheme, using seeds from biotypes (glyphosate-resistant and glyphosate-susceptible) with monthly periods of removal from field (one to 12 months). Seeds of each biotype were placed on the soil surface and covered with soil and straw to simulate no-till conditions. The percentage of germinated, dormant, and dead seeds was evaluated every 30 days. The ryegrass seed bank of glyphosate-susceptible and glyphosate-resistant biotypes was reduced to 11 and 15% of dormant seeds, respectively, at the end of 12 months. However, there was no variation in germination, dormancy, and seed mortality between susceptible and glyphosate-resistant ryegrass. Seeds of glyphosate-resistant biotype and susceptible showed germination behavior with similar dynamics in the soil over a period of 12 months.