Coexistence in Maize: Do Nonmaize Buffer Zones Reduce Gene Flow between Maize Fields?

Abstract

One approach to ensuring coexistence of genetically modified (GM) and conventional maize (Zea mays L.) is reducing pollen‐mediated gene flow. Field experiments were conducted in 2005 at four sites in Germany to compare a tall sunflower crop (Helianthus annuus L.) vs. a short clover–grass crop (Trifolium pratense L. and Lolium spp.) with regard to their ability to reduce outcrossing when grown as buffer between pollen donor and recipient maize plots. Three different maize test systems were used: (i) quantification of a donor transgene via real‐time polymerase chain reaction (rt PCR), (ii) a nontransgenic test system based on a dominant kernel color trait, and (iii) a molecular marker test system based on rt PCR quantification of a cultivar‐specific nontransgenic DNA sequence. We found that the three test systems yielded comparable results concerning buffer‐crop effectiveness and edge effects. There was no difference in outcrossing rates when comparing the sunflower vs. clover–grass buffer crop. Outcrossing rates downwind beyond 12 m sunflower as buffer crop within adjacent 12‐m‐wide recipient maize were 4.2, 11.7, and 3.8% for the GM maize, the kernel color, and the molecular marker test system compared with clover–grass with 4.3, 9.6, and 3.6%. Pronounced edge effects were detected at the edges of recipient maize fields. Based on the present study, growing sunflower as a tall crop between GM and non‐GM maize cannot be recommended as an appropriate coexistence measure.

Coexistence of genetically modified (GM) and non-GM crops in the European Union. A review

“…The extent of cross-fertilisation is reduced much more effectively by a pollen barrier than by an isolation distance of bare ground of the same width (Della Porta et al, 2008). Many research results confirmed that the outer plant rows in a recipient maize field function as a zone that safeguards the centre of recipient fields (Gustafson et al, 2006;Messeguer et al, 2006;Ganz et al, 2007;Sabellek et al, 2007;van de Wiel et al, 2007;Weber et al, 2007;Weekes et al, 2007;Langhof et al, 2008). With a maize barrier of 10-20 m, almost none of the remaining maize harvest in the field contains more than 0.9% GM material.…”

“…Recently, Della Porta et al (2008) demonstrated that surrounding the recipient field with just two maize rows resulted in the same reduction in cross-fertilisation levels as surrounding the pollen donor with twelve maize rows. Because a maize pollen barrier around the donor is only trapping pollen that flies low and that is not likely to disperse far, the effect of a pollen barrier surrounding the donor field is thought to remain very local and limited (Gustafson et al, 2006;Kuparinen et al, 2007;Langhof et al, 2008). Moreover, in the case of GM herbicide-resistant maize, the cultivation of GM and non-GM maize in the same field might create practical challenges since two different weed management regimes would have to be applied on a single field.…”

Adventitious presence of GMOs in maize in the view of coexistence

“…The orientation of fields is also very important, since the edge effects may contribute considerably to the average cross-fertilization rates in the whole receptor field. Langhof et al (2008) pointed out that pronounced edge effects contribute disproportionally to the overall GM content of the harvest.…”

“…non-maize crop could be planted. The study of Langhof et al (2008) included clover-grass as short crop and a sunflower as a tall crop. The comparison of the effectiveness of the two crops showed that the crossfertilization rates downwind did not differ between the crops.…”

The impact of GM seed admixture on the non-GM harvest product in maize (Zea mays L.)

“…These include cross-pollination between adjacent fields, seed dispersal from volunteers and mechanical transfer at sowing, harvesting, transport and storage operations (Brookes et al 2004). Until now GM cross pollination was studied only between fields over short and long distances (Bannert and Stamp 2007;Della Porta et al 2008;Devos et al 2005;Ma et al 2004;Langhof et al 2008) and the problem of in-field cross-pollination due to GM seed impurity was completely neglected, even though the problematic in conventional seed lots is well known since long. Seed lots are starting points in an ever increasing supply food and feed chain.…”