Search

In addition to or as substitution for a regulated isolation distance, conventional maize (Zea mays L.) border rows at the genetically modified (GM) maize field edge are considered as feasible measure to ensure coexistence between GM and conventional or organic maize. Therefore, we examined the effectiveness of 9-m-and 18-m-wide non-GM maize borders at the GM maize field edge on outcrossing rates into a neighboring non-GM maize field. One field experiment each was conducted in 2008 at three sites in Germany using a field orientation representing a worst-case scenario concerning wind direction. In each case, the distance between GM and non-GM maize fields was 51 m. At two sites, sizes of GM and non-GM maize fields were 0.8 ha, respectively, and at the third site 0.5 ha (GM) and 0.3 ha (non-GM). The GM percentages of individual samples taken at recipient field depths between 0 and 90 m were quantified by real-time polymerase chain reaction. Overall, no pollen-mediated gene flow reducing effect of border rows was observed in the present study, although synchrony of anthesis between GM maize and border row maize was given at each site. Calculated GM contents of the total non-GM fields harvest were always below the European Union labeling threshold of 0.9%. In consequence, planting 9-m- or 18-m-wide conventional maize border rows at the GM field edge is no reliable coexistence measure, at least if combined with an isolation distance.

With 3 figures and 4 tables Abstract At the field scale, pollen flow between adjacent fields limits the potential of coexistence of different farming production systems, especially for allogamous crops like oilseed rape whose pollen is disseminated by insects or wind. In this article, we examine the efficiency of cleistogamy in an oilseed rape line which showed between 90% and 99% of flowers closed at flowering, in limiting deposition of allo-pollen. Five trials were established, consisting of two adjacent blocks, the one sown with the cleistogamous low-erucic acid line and the other with a classically flowering high-erucic acid line, used as source of contaminating pollen, itself artificially contaminated with a 1% mix of cleistogamous plants. Analyses showed that cross-fertilization rates of cleistogamous plants, estimated through erucic acid contents of seeds collected from them, were lower than those generally observed in oilseed rape: it averaged 10.1% on isolated plants within the erucic blocks, reached to the maximum 14% immediately adjacent to the erucic block, then decreased exponentially at higher distances. Cleistogamy appeared therefore as one imperfect means of gene bio-containment.

The most reliable and practicable measure in assuring coexistence in respect to pollenmediated gene fl ow from genetically modifi ed (GM) to conventional maize (Zea mays L.) is an isolation distance separating GM and non-GM fi elds. Therefore, we tested distances between 24 and 102 m at three sites in northern Germany using a fi eld orientation representing a worst case scenario concerning wind direction. During the 3 yr of fi eld trials the highest levels of gene fl ow occurred at the site and year with the longest fl owering synchrony and the strongest wind blowing constantly from the GM to the non-GM fi eld. It was shown that the GM content of a neighboring non-GM maize fi eld is mainly determined by wind speed and direction as well as by non-GM maize fi eld depth. Based on the maximum outcrossing data obtained it can be concluded that for non-GM maize fi elds being 200 m deep or more an isolation distance of 50 m is suffi cient to keep the GM content of the total fi elds grain harvest below the European Union (EU) labeling threshold of 0.9%. However, non-GM grain maize fi elds with smaller fi eld depth require larger isolation distances or additional coexistence measures. In most cases discarding 6 m of the GM maize facing non-GM maize fi eld edge has proven to be such a valuable measure. In silage maize production 50 m isolation distance is adequate even for non-GM maize fi eld depths down to 50 m. We recommend fl exible separation distances in dependence on non-GM maize fi eld depth to comply with EU coexistence requirements.

Maize (Zea mays L.) Plus-Hybrids are a blend of cytoplasmic male-sterile (CMS) hybrids and unrelated male-fertile hybrids ensuring pollination of the whole stand. Combining potential benefits of male sterility (CMS effect) and allopollination (xenia effect), they often outperform the corresponding male-fertile sib-pollinated hybrids in terms of yield. The combining abilities of five CMS hybrids and eight pollinators were investigated in a factorial split-plot design in 12 environments in four countries and two years. The plant material from different breeders represented the three types of male-sterile cytoplasm. Plus-Hybrids increased grain yield, on average, by 10% or more and by up to 20% in specific environments. Three highly responsive CMS hybrids and four generally good pollinators were identified. The Plus-Hybrid effect affected both yield components, CMS leading mainly to a higher number of kernels (KN) and the xenia effect mainly to an increase in the thousand kernel weight (TKW). Despite some differences in the response of the three types of CMS, the effect of the cytoplasm was not significant. While the CMS effect depended strongly on environment, the xenia was consistent in all environments but its extent varied. As well as increasing yield, we can expect that Plus-Hybrids can make a large contribution to the coexistence of transgenic and conventional maize by biocontainment, that is, eliminating or reducing the release of transgenic pollen in Bacillus thuringiensis (Bt) maize or herbicide-tolerant (HT) maize.

Cytoplasmic male sterility (CMS) is a maternally transmitted trait, whereby a plant is unable to produce viable pollen. Studies have revealed that this trait is a tool for enabling effi cient and reliable coexistence between genetically modified (GM) and non-GM cultivation by biocontainment of GM maize (Zea mays L.) pollen. Maize has three types of male-sterile cytoplasm (T, S, and C), the fertility of which can be restored by nuclear rf genes or by interactions with the environment. Twenty-two CMS versions of modern European maize hybrids were evaluated in 17 environments in Switzerland, France, and Bulgaria, with two or three sowing dates, in 2005 and 2006. Stable and unstable male sterility occurred in all three CMS types. T-cytoplasm hybrids were the most stable, while S-cytoplasm hybrids often showed partial restoration of fertility. C-cytoplasm was similar to T-cytoplasm with regard to maintaining male sterility. Climatic factors, especially air temperature, evapotranspiration, and water vapor, during the 10 d before anthesis as well as during anthesis, were correlated positively or negatively with the partial reversion to male fertility of CMS hybrids, indicating an interaction between genetic and climatic factors. This study illustrates that T- and C-cytoplasm in particular open up viable prospects for containing transgenic pollen, especially for Bt-maize.

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 sun-flower 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.