Stratification Requirements for Seed Dormancy Alleviation in a Wetland Weed

Echinochloaoryzicola(syn.E. phyllopogon) is an exotic weed of California rice paddies that has evolved resistance to multiple herbicides. Elimination of seedlingsthroughcertain weed control methods can limit the spread of this weed, but is contingent on accurate predictions of germination and emergence timing, which are influenced by seed dormancy levels. In summer annuals, dormancy can often be relieved through stratification, a period of prolonged exposure to cold and moist conditions. We used population-based threshold models to quantify the effects of stratification on seed germination of four E. Oryzicola populations at a range of water potential (Psi) and oxygen levels. We also determined how stratification temperatures, moisture levels and durations contributed to dormancy release. Stratification released dormancy by decreasing base Psi and hydrotimerequired for germination and by eliminating any germination sensitivity to oxygen. Stratification also increased average germination rates (GR), which were used as a proxy for relative dormancy levels. Alternating temperatures nearly doubled GR in all populations, indicating that seeds could be partially dormant despite achieving high final germination percentages. Stratification at Psi=0 MPa increased GR compared to stratification at lower water potentials, demonstrating that Psi contributed to regulating dormancy release. Maximum GR occurred after 2-4 weeks of stratification at 0 MPa; GR were often more rapid for herbicide-resistant than for herbicide-susceptible seeds, implying greater dormancy in the latter. Manipulation of field conditions to promote dormancy alleviation of E. oryzicola seeds might improve the rate and uniformity of germination for seed bank depletion through seedling weed control. Our results suggest field soil saturation in winter would contribute towards E. oryzicola dormancy release and decrease the time to seedling emergence.