Stratification Requirements for Seed Dormancy Alleviation in a Wetland Weed

Abstract

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 (Ψ) and oxygen levels. We also determined how stratification temperatures, moisture levels and durations contributed to dormancy release. Stratification released dormancy by decreasing base Ψ 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 Ψ = 0 MPa increased GR compared to stratification at lower water potentials, demonstrating that Ψ 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.

Effect of soil moisture during stratification on dormancy release in seeds of five common weed species

“…However, Boddy et al . () suggested that winter flooding may help control Echinochloa oryzicola Vasinger. in rice fields in California (USA) by decreasing seed dormancy and time to seedling emergence in spring, provided wintertime soil saturation can be maintained for an extended period of time.…”

“…Moreover, cool season irrigation traditionally has been used to improve perennial crops in the study area thereby increasing the chance of subjecting seeds to too much soil moisture content for dormancy breakage to occur. However, Boddy et al (2013) suggested that winter flooding may help control Echinochloa oryzicola Vasinger. in rice fields in California (USA) by decreasing seed dormancy and time to seedling emergence in spring, provided wintertime soil saturation can be maintained for an extended period of time.…”

Secondary dormancy induction and release inBromus tectorumseeds: the role of temperature, water potential and hydrothermal time

“…The relationship between chilling temperature and primary dormancy release has been studied in several species. For example, for Nothofagus species, there was no difference in efficacy for temperatures from 0.5 to 4°C (Arana et al ., 2016), whereas for the summer annual rice weed Echinochloa oryzicola in the Mediterranean climate of California, 7.5°C was somewhat more effective for releasing primary dormancy than either 2.5 or 5°C (Boddy et al ., 2013). For recalcitrant seeds of Aesculus hippocastaneum , Pritchard et al .…”

Weed Seed Dormancy: The Ecophysiology and Survival Strategies

“…Echinochloa oryzicola dormancy is possibly relieved through stratification. Stratification temperatures, moisture levels, and durations contributed to its seed dormancy released by decreasing hydrotime required for germination and by eliminating any germination sensitivity to oxygen [61]. Alternating temperatures nearly doubled germination rate in all weed populations of this species.…”

“…than for herbicide-susceptible seeds, implying greater dormancy in the latter. Germination rate was often more rapid for herbicide-resistant than for herbicide-susceptible seeds, implying greater dormancy in the latter [61]. Population shift in life cycle has been previously discussed as shown by Senecio vulgaris L. in order to avoid herbicide phytotoxicity.…”