Biosecurity and the potential effects of transgenic crops in centers of origin in Mexico

Background/Question/Methods

Over the last 20 years, the biotechnology industry has developed genetically modified (GM) organisms for agriculture with important consequences to the world economy. Today, GM plants are planted in over 100 million hectares in industrialized and developing countries.  Since 1992, Mexican authorities allowed the introduction of transgenic crops and today over 22 GM species are cultivated.  Mexico is center of origin of the wild relatives of many transgenic crops and hybridization is possible between them.  Gene flow between GM and wild plants is common, raising concerns about the possible transmission of traits from GM crops to wild populations. However, the ecological impacts of escaped transgenes are not well documented.  Introgression of transgenes that promote resistance to pesticides, virus, and herbivores in GM plants into wild populations may generate hybrids that may become invasive weeds.

First, we analyzed the current distribution of GM crops in Mexico and the posible areas for introgression with wild relatives.  We also evaluated gene flow and hybridization between Cucurbita pepo GM plants and the wild relative C. argyrosperma sororia.  Mexico is the center of origin of Cucurbita pepo and C. argyrosperma. This study will provide important information for biosecurity legislation that is currently lacking.

Results/Conclusions

The biotechnology industry has developed GM cultivars of squash resistant to virus.  The release of GM Cucurbita pepo by the USDA considered that resistance genes to virus would not be able to escape and persist in natural populations.  However, no studies have evaluated the consequences of GM crop release in the center of origin of the wild relative.  We conducted a series of crosses with mixtures of pollen from transgenic and wild pollen donors.  Seeds obtained from crosses were planted and paternity was determined using phenotypic and molecular markers and progeny vigor was measured.  Our results indicate that Cucurbita pepo GM hybridize with the wild species of Cucurbita argyrosperma sororia.  Transgenic genes resistant to virus are transmitted to F1 and F2 hybrids and slightly deviate from Mendelian inheritance.  Microgametophyte certation of C. argyrosperma sororia may affect fertilization success of GM Cucurbita but transgenic hybrid progeny are produced at a high proportion.  The analysis of progeny vigor indicates that hyrbid transgenics germinate and produce the first true leaf at the same rate of the wild species, C. argyrosperma sororia.  Transgenic hybrids produced greater leaf area than the wild progenitor showing hybrid vigor.  Hybrids are also fertile and produce viable offspring.