Assessment of potential environmental risks of transgene flow in smallholder farming systems in Asia: Brassica napus as a case study in Korea

The key determinant for forming pollen density and using crop barriers to mitigate wind-blown pollen dispersal in alfalfa (Medicago sativa L.)

The potential for commercial cultivation of genetically engineered (GE) alfalfa has raised ecological concerns due to the possibility of introgression of GE alleles into conventional populations. The main objectives of this study were to determine the key affecting factors (i.e. size of pollen source, number of pollinating bees) on forming alfalfa pollen cloud density and test the mitigating effect using maize barrier rows on alfalfa pollen dispersal. The results showed that the mean pollen densities of alfalfa pollen source (Ø = 10 or 20 m) were statistically similar when treated with the same number of worker bumblebees and increased accordingly with increasing the worker bees (887 and 853 pollens m-3 h-1 for Ø = 10 and 20 m with 100-150 worker bees, respectively; 1040 and 1070 pollens m-3 h-1 for the two plots with 200-300 worker bees, respectively), demonstrating that the number of worker bees but not the size of the pollen source was the key determinant for forming alfalfa pollen density. A maize barrier row established at 0.5 m from the alfalfa edge consistently decreased downwind pollen densities (percent pollen density of pollen source) to 0.2-4.4 % at 1-9 m compared to 3.4-25.4 % and 7.5-37.8 % at the same distance range for the upwind and downwind sites without maize barrier rows, respectively. Based on the pods formed on the emasculated alfalfa flowers (due to pollen dispersal) located at various distances from the pollen source and subsequent prediction model, the pollen density threshold value for fertilizing alfalfa recipient under the wind-blown condition was determined of 65.8 pollens m-3 h-1 at 14.7 m from the pollen source edge. The results would help in understanding the pollination biology (minimum pollen density for fertilizing alfalfa recipient ovule) and the process of pollen-mediated gene flow and helpful in developing management strategies to reduce the pollen density and thus mitigate the gene flow in alfalfa.

A Review of the Unintentional Release of Feral Genetically Modified Rapeseed into the Environment

Simple Summary

With the advent of genetic engineering technology, the development and cultivation of genetically modified (GM) crops has increased. They were mainly developed for high yielding, herbicide resistance, and tolerance against different biotic and abiotic stresses. Rapeseed, also known as canola, was developed mainly for herbicide resistance and to increase the production of canola oil. Since it forms weedy, feral populations and has a proven ability to hybridize with its close relatives, it is important to manage the GM crops’ cultivation and spread, especially the rapeseed. Several studies have reported that the spread of GM rapeseed in non-GM fields and road verges is possible due to transport and agronomic practices, and it may become a weed. Hence, in this review, we summarized the cases of unintentional spread of feral GM rapeseed in the fields and road verges. In addition, we made recommendations for the effective management of feral GM and non-GM rapeseed in agricultural fields and along roads.

Abstract

Globally, the cultivation area of genetically modified (GM) crops is increasing dramatically. Despite their well-known benefits, they may also pose many risks to agriculture and the environment. Among the various GM crops, GM rapeseed (Brassica napus L.) is widely cultivated, mainly for oil production. At the same time, B. napus possesses a number of characteristics, including the ability to form feral populations and act as small-seeded weeds, and has a high potential for hybridization with other species. In this review, we provide an overview of the commercialization, approval status, and cultivation of GM rapeseed, as well as the status of the feral rapeseed populations. In addition, we highlight the case studies on the unintentional environmental release of GM rapeseed during transportation in several countries. Previous studies suggest that the main reason for the unintentional release is seed spillage during transport/importing of rapeseed in both GM rapeseed-cultivating and -non-cultivating countries. Despite the fact that incidents of unintentional release have been recorded often, there have been no reports of serious detrimental consequences. However, since rapeseed has a high potential for hybridization, the possibilities of gene flow within the genus, especially with B. rapa, are relatively significant, and considering their weedy properties, effective management methods are needed. Hence, we recommend that specific programs be used for the effective monitoring of environmental releases of GM rapeseed as well as management to avoid environmental and agricultural perturbations.

Increased Longevity and Dormancy of Soil-Buried Seeds from Advanced Crop–Wild Rice Hybrids Overexpressing the EPSPS Transgene

Simple Summary

Estimating the survival and reproductive ability caused by a transgene moved from a genetically engineered (GE) crop to its wild relative populations through gene flow plays an important role in assessing the potential environmental risks of the GE crop. Such estimation has essentially focused on the survival and reproduction-related characteristics above the ground, but with little attention to the GE seeds shattered in the soil seed banks. We demonstrated that the herbicide-resistant transgene overexpressing the rice endogenous EPSP enzyme increased the survival and longevity of the GE crop–wild (Oryza rufipogon) hybrid seeds in soil seed banks. In addition, enhanced survival and longevity of the GE hybrid seeds are likely associated with increases in seed dormancy and a growth hormone (auxin) via overexpressing the EPSPS transgene. Therefore, the EPSPS transgene can persist in the soil seed banks and spread in the environment, causing unwanted environmental impacts.

Abstract

Estimating the fitness effect conferred by a transgene introgressed into populations of wild relative species from a genetically engineered (GE) crop plays an important role in assessing the potential environmental risks caused by transgene flow. Such estimation has essentially focused on the survival and fecundity-related characteristics measured above the ground, but with little attention to the fate of GE seeds shattered in the soil seed banks after maturation. To explore the survival and longevity of GE seeds in soil, we examined the germination behaviors of crop–wild hybrid seeds (F₄–F₆) from the lineages of a GE herbicide-tolerant rice (Oryzasativa) line that contains an endogenous EPSPS transgene hybridized with two wild O. rufipogon populations after the seeds were buried in soil. The results showed significantly increased germination of the GE crop–wild hybrid seeds after soil burial, compared with that of the non-GE hybrid seeds. Additionally, the proportion of dormant seeds and the content of the growth hormone auxin (indole-3-acetic acid, IAA) in the GE crop–wild hybrid seeds significantly increased. Evidently, the EPSPS transgene enhances the survival and longevity of GE crop–wild rice seeds in the soil seed banks. The enhanced survival and longevity of the GE hybrid seeds is likely associated with the increases in seed dormancy and auxin (IAA) by overexpressing the rice endogenous EPSPS transgene. Thus, the fate of GE seeds in the soil seed banks should be earnestly considered when assessing the environmental risks caused by transgene flow.

Environmental risk assessment of glufosinate-resistant soybean by pollen-mediated gene flow under field conditions in the region of the genetic origin

Pollen-mediated gene flow of genetically modified crops to their wild relatives can facilitate the spread of transgenes into the ecosystem and alter the fitness of the consequential progeny. A two-year field study was conducted to quantify the gene flow from glufosinate-ammonium resistant (GR) soybean (Glycinemax) to its wild relative, wild soybean (G. soja), and assess the potential weed risk of hybrids resulting from the gene flow during their entire life cycle under field conditions in Korea, where wild soybean is the natural inhabitant. Pollen-mediated gene flow from GR soybeans to wild soybeans ranged from 0.292% (mixed planting) to 0.027% at 8 m distance. The log-logistic model described the gene flow rate with increasing distance from GR soybean to wild soybean; the estimated effective isolation distance for 0.01% gene flow between GR and wild soybeans was 37.7 m. The F1 and F2 hybrids exhibited the intermediate characteristics of their parental soybeans in their vegetative and reproductive stages. Canopy height and stem length of hybrids were close to those of wild soybean, which shows an indeterminate growth; the numbers of flowers, pods, and seeds per hybrid plant were close to those of wild soybean and significantly higher than those of GR soybean. Seed longevity of F2 hybrid plants was also intermediate but significantly greater than that of GR soybean due to high seed dormancy. Our results suggest that transgenes of the GR soybean might disperse into wild populations and persist in the agroecosystem of the genetic origin regions due to the pollen-mediated gene flow and the relatively high fitness of the hybrid progeny.

Evaluating the probability of CRISPR-based gene drive contaminating another species

The probability D that a given clustered regularly interspaced short palindromic repeats (CRISPR)-based gene drive element contaminates another, nontarget species can be estimated by the following Drive Risk Assessment Quantitative Estimate (DRAQUE) Equation: D = h y b + t r a n s f × e x p r e s s × c u t × f l a n k × i m m u n e × n o n e x t i n c t with hyb = probability of hybridization between the target species and a nontarget species; transf = probability of horizontal transfer of a piece of DNA containing the gene drive cassette from the target species to a nontarget species (with no hybridization); express = probability that the Cas9 and guide RNA genes are expressed; cut = probability that the CRISPR-guide RNA recognizes and cuts at a DNA site in the new host; flank = probability that the gene drive cassette inserts at the cut site; immune = probability that the immune system does not reject Cas9-expressing cells; nonextinct = probability of invasion of the drive within the population. We discuss and estimate each of the seven parameters of the equation, with particular emphasis on possible transfers within insects, and between rodents and humans. We conclude from current data that the probability of a gene drive cassette to contaminate another species is not insignificant. We propose strategies to reduce this risk and call for more work on estimating all the parameters of the formula.

Using a zero-inflated model to assess gene flow risk and coexistence of Brassica napus L. and Brassica rapa L. on a field scale in Taiwan

BACKGROUND

The cropping area of genetically modified (GM) crops has constantly increased since 1996. However, currently, cultivating GM crops is associated with many concerns. Transgenes are transferred to non-GM crops through pollen-mediated gene flow, which causes environmental problems such as superweeds and introgressive hybridization. Rapeseed (Brassica napus L.), which has many GM varieties, is one of the most crucial oil crops in the world. Hybridization between Brassica species occurs spontaneously. B. rapa grows in fields as a weed and is cultivated as a crop for various purposes. Both B. rapa weeds and crops participate in gene flow among rapeseed. Therefore, gene flow risk and the coexistence of these two species should be studied.

RESULTS

In this study, field experiments were conducted at two sites for 4 years to evaluate gene flow risk. In addition, zero-inflated models were used to address the problem of excess zero values and data overdispersion. The difference in the number of cross-pollination (CP) events was nonsignificant between upwind and downwind plots. The CP rate decreased as the distance increased. The average CP rates at distances of 0.35 and 12.95 m were 2.78% and 0.028%, respectively. In our results, zero-inflated negative binomial models were comprehensively superior to zero-inflated Poisson models. The models predicted isolation distances of approximately 1.36 and 0.43 m for the 0.9% and 3% threshold labeling levels, respectively.

CONCLUSIONS

Cultivating GM crops is prohibited in Taiwan; however, the study results can provide a reference for the assessment of gene flow risk and the coexistence of these two species in Asian countries establishing policies for GM crops.

Enhanced yield performance of transgenic cry1C* rice in saline-alkaline soil

China has a large area of saline-alkaline land that can be utilized for the cultivation of transgenic rice. Therefore, the growth and reproductive behavior of transgenic rice are not only a problem for production that needs to be resolved, but also an important aspect of environmental risk assessment for saline alkali soil. In the present study, an insect-resistant transgenic cry1C* rice, T1C-19, was grown in farmland and saline-alkaline soils. The transcription and translation of the exogenous cry1C*, and vegetative and reproductive fitness, such as plant height, tiller number, biomass, filled grain number and weight per plant, were assessed. Our findings indicated that the transcription and translation of exogenous cry1C* gene in T1C-19 rice grown in saline-alkaline soil were lower than that grown in farmland; however, the correlation was not significant. The vegetative and reproductive growth abilities of T1C-19 were lower than that of the parental rice, Minghui63 (MH63), in farmland. In alkaline-saline soil, except for tiller number and biomass, there were no significant differences between T1C-19 and MH63 in other vegetative indices. In contrast, the reproductive indices of T1C-19 were significantly higher than those of MH63. The results suggested that T1C-19 had a strong reproductive capacity, and significantly reduced the loss of yield caused by insects, thereby leading to a higher yield than that of MH63 grown in saline-alkaline soils. This may promote the cultivation of saline-alkaline soil to permit farming of T1C-19 in China in the future, despite the possible increased ecological risks.