Sexual compatibility of transgenic soybean and different wild soybean populations

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.

Assessment of Gene Flow Through Detection of SexualCompatibility Between Transgenic Rice with barand Echinochloa crusgalli var.mitis

The possibility of gene flow between two varieties of transgenic rice with bar gene (Y0003 and 99-t) (male) and barnyard grass(Echinochloa crusgalli var. mitis ) (female) was studied by means of reproductive biology. The germination and growth of rice pollen grains on barnyard grass stigmas at 30 min, and 1-4 h after crossing by hand were observed with an optical microscope. The results were compared with the germination and growth of barnyard grass pollen grains at the corresponding time after self-pollination. The results showed that germination and growth of the pollen grains of the two varieties were similar on barnyard grass stigmas, but differed significantly from self-pollination of barnyard grass. Pollen grains germinated and pollen tubes penetrated stigmas normally, and the number of pollen grains being condensing or releasing their inclusions or having released them increased with the time after self-pollination. Pollen grains of transgenic rice on the stigmas of barnyard grass couldn't germinate or grow normally after crossing, neither could they penetrate the stigmas of barnyard grass. Therefore, it could be concluded that the sexual incompatibility between transgenic rice with bar gene and barnyard grass is due to the rice pollen being unable to penetrate the stigma of barnyard grass. Further proof of incompatibility lies in the fact that the emasculated barnyard grass pollinated with the rice pollen grains could not seed.