Rice, the main food crop in China, has been sporadically reported to suffer from weedy rice infestation.  However, the overall occurrence and distribution pattern of Chinese weedy rice remains unclear because a systematic survey has not been conducted.  In order to reveal the infestation of Chinese weedy rice, a field survey was conducted in 999 sampling sites all over the rice-growing regions in China from 2009 to 2016 using seven-scale visual scoring of the level of weed infestation.  Weedy rice was found 39% occurrence incidence in a total of 387 sites.  The sampling sites with 50% or higher overall weedy rice infestation index mainly radiated from Jiangsu, Heilongjiang, Ningxia and Guangdong to the whole East China, Northeast China, Northwest China and South China.  A total of 45 morphological characters from 287 populations (collected simultaneously with the field survey) out of those occurred sites were observed and analyzed using multivariate analysis in common gardens with the same cultivation conditions in 2017 and 2019.  Canonical correlation analysis showed that 45 morphological characters were significantly related to the latitude, mean temperature, minimum temperature, precipitation and mean diurnal range factors.  The 287 weedy rice populations were divided into three morphological groups with climate-dependent geographical differentiation: strong tiller type only in Jiangsu, large leaf type in South China and Central China and large grain type mainly in North China.  Weedy rice seriously infested rice fields and had a geography, climate and cultivated rice type-dependent morphological and biotype differentiation in China.  It is suggested to pay attention to the harmfulness of weedy rice and adopt comprehensive control strategies.

The introduction of genetically modified (GM) soybean into farming systems raises great concern that transgenes from GM soybean may flow to endemic wild soybean via pollen.  This may increase the weediness of transgenic soybean by increasing the fitness of hybrids under certain conditions and threaten the genetic diversity of wild soybean populations.  Although pollen-mediated gene flow between GM crops and wild relatives is dependent on many factors, the sexual compatibility (SC) determined by their genetic backgrounds is the conclusive factor.  The considerable genetic variation among wild soybean populations may cause compatibility differences between different wild and cultivated soybeans.  Thus, an evaluation of the SC between transgenic soybean and different wild soybeans is essential for assessing the environmental consequences of cultivated soybean–wild soybean transgene flow.  The podding and seed sets were assessed after artificial hybridization using transgenic glyphosate-resistant soybean as the paternal parent and 18 wild soybean populations as the maternal parents.  Then, the average number of filled seeds produced in 200 flowers (AFS) was calculated for each wild soybean under natural self-pollination as well as under artificial crossing with transgenic soybean.  Finally, the index of cross-SC was calculated (ICSC) as the ratio of the AFS of wild soybean artificially crossed with transgenic soybean and the AFS of naturally self-pollinated wild soybean.  The results demonstrated that after self-pollination and crossing with transgenic soybean, the average podding rates of 18 wild soybean populations ranged within 96.50–99.50% and 4.92–18.03%, and the average filled seed numbers per pod varied from 1.70 to 2.69 and 0.20 to 0.48, respectively.  The results showed that approximately 89% of wild soybeans displayed either medium or higher than medium SC with transgenic soybean (ICSC>1.0%).  This implied the high possibility of gene flow via pollen from transgenic soybean to wild soybean.

Stacked (insect and herbicide resistant) transgenic rice T1c-19 with cry1C*/bar genes, its receptor rice Minghui 63 (herein MH63) and a local two-line hybrid indica rice Fengliangyou Xiang 1 (used as a control) were compared for agronomic performance under field conditions without the relevant selection pressures. Agronomic traits (plant height, tiller number, and aboveground dry biomass), reproductive ability (pollen viability, panicle length, and filled grain number of main panicles, seed set, and grain yield), and weediness characteristics (seed shattering, seed overwintering ability, and volunteer seedling recruitment) were used to assess the potential weediness without selection pressure of stacked transgene rice T1c-19. In wet direct-seeded and transplanted rice fields, T1c-19 and its receptor MH63 performed similarly regarding vegetative growth and reproductive ability, but both of them were significantly inferior to the control. T1c-19 did not display weed characteristics; it had weak overwintering ability, low seed shattering and failed to establish volunteers. Exogenous insect and herbicide resistance genes did not confer competitive advantage to transgenic rice T1c-19 grown in the field without the relevant selection pressures.

Horseweed (Conyza canadensis), an invasive alien weed, is one of the main weeds in orchards in China. Althoughglyphosate has been used for control of horseweed and many other weeds in orchards for more than 25 years in China, acase of glyphosate-resistant horseweed has not been identified in orchard in China so far despite glyphosate-resistanthorseweed cases have been reported in some other countries. Seeds of 25 horseweed populations were collected fromdifferent orchards with different glyphosate application history. Potted seedlings with 11-13-leaf growth stage weretreated with glyphosate at 0.035, 0.07, 0.14, 0.28, 0.56, 1.12, 2.24, 4.48, and 8.96 kg a.i. ha-1. The dosage dependenceresponse curve of each population was constructed with Log-logistic dose response regression equations. The ED50value of each population was calculated and compared with the susceptible population from China. Different populationshad different relative glyphosate-resistant levels which increased with the number of years of glyphosate application.Two populations with the highest resistance levels, 8.28 and 7.95 times, were found in Ningbo, Zhejiang Province, China,where glyphosate was used for weed control in orchards twice each year for 15 yr. The two resistant populationsaccumulated approximately two to four times less shikimic acid than the two susceptible populations 48 h after glyphosateapplication.