Weedy rice (Oryza sativa f. spontanea) is one of the three worst paddy weeds in most rice growing areas.  The unexpected heavy infestation is derived from a persistence of soil seed bank of weedy rice, which the shattered seeds chiefly feed back to.  Information on soil seed bank dynamics is imperative to predict the infestation of weeds.  In the present paper, the effect of rotary tillage on weedy rice seed bank structure was studied first, and a burial experiment of marked seeds was conducted to observe the overwintering survival, seed viability and seedling emergence of weedy rice.  The results showed that the proportion of weedy rice seeds in deeper soil increased but seedling emergence decreased with increasing plowing depth.  The viability of weedy rice seeds decreased as the burial duration time extended but more slowly in deeper soil layers.  Additionally, there was no significant effect of burial density on seed viability.  Moreover, the logistic model fitted well (R²≥0.95, P≤0.01) with the depressive trends of seed viability with increasing burial time under all burial depths and densities which can provide us further information about seed survival.  In field experiments, number of seedling emergence significantly decreased as seed burial depth increased, conversely, proportion of seedling emergence increased as seed burial density decreased.  This study has important implications for determining strategies for weedy rice management by exhausting its seed bank through the alteration of tillage practices.

Compared to single-trait transgenic crops, stacked transgenic plants may be more prone to become weedy, and transgene flow from stacked transgenic plants to weedy relatives may pose a potential environmental risk because these hybrids could be more advantageous under specific environmental conditions.  Evaluation of the potential environmental risk caused by stacked transgenes is essential for assessing the environmental consequences caused by crop-weed transgene flow.  The agronomic performance of fitness-related traits was assessed in F₁+ (transgene positive) hybrids (using the transgenic line T1c-19 as the paternal parent) in monoculture and mixed planting under presence or absence glufosinate pressure in the presence or absence of natural insect pressure and then compared with the performance of F₁– (transgene negative) hybrids (using the non-transgenic line Minghui 63 (MH63) as the paternal parent) and their weedy rice counterparts.  The results demonstrated that compared with the F₁– hybrids and weedy rice counterparts, the F₁+ hybrid presented higher performance (P<0.05) or non-significant changes (P>0.05) under natural insect pressure, respectively, lower performance (P<0.05) or non-significant changes (P>0.05) in the absence of insect pressure in monoculture planting, respectively.  And compared to weedy rice counterparts, the F₁+ hybrid presented higher performance (P<0.05) or non-significant changes (P>0.05) in the presence or absence of insect pressure in mixed planting, respectively.  The F₁+ hybrids presented non-significant changes (P>0.05) under the presence or absence glufosinate pressure under insect or non-insect pressure in monoculture planting.  The all F₁+ hybrids and two of three F₁– hybrids had significantly lower (P<0.05) seed shattering than the weedy rice counterparts.  The potential risk of gene flow from T1c-19 to weedy rice should be prevented due to the greater fitness advantage of F₁ hybrids in the majority of cases.