Weedy Risk Assessment of Hybrids Resulted from Gene Flow from LM Soybean to Wild Soybean

Abstract

Although living modified (LM) crops have not been allowed for agricultural cultivation in Korea, increased import of LM crops for food processing and animal feeding has raised concerns on unintentional escape of LM crops and following eventual risks including gene flow from LM crops to their relatives and the weediness of hybrids resulted from gene flow. Soybean (Glycine max) is a legume species native to East Asia including Korea where wild soybean (Glycine soja) inhabits natural and agricultural ecosystem and often coexists with cultivated soybean in a same field, suggesting that unintentional escape of LM soybean may cause gene flow to relative soybean species and sequential consequences. However, no or little effort has been made to assess potential risks. Therefore, this study was conducted to assess potential gene flow from LM soybean to wild soybean and weediness of hybrids resulted from gene flow in Korean agro-ecosystem. Two year field experiments conducted in the LMO field (authorization number: RDA-AB-2011-014) revealed potential gene flow from LM soybean (♂, ATSIZ #6) to wild soybean (♀, IT 182932) planted at various distances between them up to 8 m. Gene flow rates were 0.191% and 0.201% in 2013 and 2014, respectively, at 0.5 m distance, and decreased rapidly increasing distance, resulting in 0.064% and 0.045% gene flow at 6 m distance. In the 2014 field study, gene flow rates were 0.292% at 0 m distance and 0.027% at 8 m distance. Non-linear regression analysis by fitting the data to the double exponential decay model enabled to simulate gene flow from LM soybean to wild soybean. These results suggest that gene flow has no year variation and gene flow from LM soybean to wild soybean can naturally occur if wild soybean inhabits about 8 m away from soybean fields. Pot and field experiments using hybrids resulted from gene flow from LM soybean to wild soybean revealed weediness of hybrid progenies, F1, F2 and F3. LM soybean showed better vegetative growth characteristics including leaf area and canopy growth except plant height, which was much greater in wild soybean and hybrid progenies due to their indeterminate and vining growths. In reproductive growth characteristics, the hybrid progenies showed better reproductive growth characteristics than LM soybean. Flower and pod numbers per plant were significantly greater in hybrid progenies than LM soybean. Pod-shattering rate and seed production of hybrids were 3 times greater than those of LM soybean. Seed longevity in field soil profiles was also significantly greater in hybrids than LM soybean. Viability of LM soybean seeds buried in soil decreased dramatically from 100 to 1.5 % after wintering, while that of hybrids still maintained high, up to 66 % after wintering. Moreover, hybrids showed much greater seed dormancy during wintering in soils, resulting in much greater seed longevity than LM soybean. Overall, hybrid progenies resulted from gene flow from LM soybean to wild soybean maintained greater portion of maternal traits associated with weediness such as seed production, pod shattering, and seed dormancy and longevity. In conclusion, two year field study revealed significant gene flow up to 8 m distance from LM soybean to wild soybean in the field condition and provided simulation model for gene flow estimation. Pot and field study with hybrids resulted from gene flow also showed high risk of weediness in hybrids due to their reproductive growth characteristics and seed dormancy and longevity. Therefore, this study would provide informative guideline to estimate risk assessment of gene flow and weediness of hybrids when LM soybean is either intentionally or unintentionally grown in agricultural crop field in Korea.