Abstract
The occurrence of volunteer maize plants in subsequent crops as well as of feral maize plants in non-agricultural areas is an essential issue in risk assessments of genetically modified (GM) maize, with regard to possible contamination of natural habitats with GM material and as contribution to the total adventitious GM content of the non-GM final product. The appearance of feral maize plants has been confirmed for non-agricultural habitats in European areas with Mediterranean climate such as Spain. However, the existence of maize volunteers and feral maize outside cultivation under Central European continental climatic conditions is considered to be extremely unlikely in those winter-cold areas. Here, field observations during 5 years (2007, 2008, 2010, 2011 and 2015) in Austria are presented that confirm the occurrence of volunteer and feral maize under Central European climatic conditions. Most of these plants produced fertile inflorescences with viable pollen and fully developed cobs. Maize kernels may reach the soil by disintegration of cobs due to disease, using crushed maize cobs for game-feeding, left overs in manure dispersed during fertilisation or from transporting and handling of crushed cobs. The evidence of volunteer and feral maize in four Federal States in Austria (Burgenland, Lower Austria, Upper Austria, Styria) emphasises the necessity to consider these hitherto under-emphasised factors in an ecological risk assessment (ERA) of GM maize as a possible source for transgenes in non-agricultural habitats, because these plants could act as bridge for the spread of GM material into semi-natural habitats. In accordance with the European Food Safety Authority (EFSA), which states that in principle maize has the potential to survive as a volunteer or feral plant also in regions with cold winters, the investigation of the frequency of their occurrence under Central European conditions should be part of future monitoring programmes in order to assess their potential for permitting transgene spread.
Highlights
Maize (Zea mays subsp. mays) is an annual monoecious crop frequently grown in many countries
As none of the sampling sites had been selected on expectations for the occurrence of volunteer and feral maize, the data presented here provide anecdotal evidence for the existence of volunteer and feral maize under Central European conditions at several locations in Austria and in several years, but they do not allow any assessment on regional distribution and abundance to be made
Feral maize plants were observed in three Austrian Federal States (Burgenland, Styria and Upper Austria; Fig. 2) in August in the years 2007, 2008, 2010 and 2015 during fieldwork for three studies [25,26,27,28]
Summary
Maize (Zea mays subsp. mays) is an annual monoecious crop frequently grown in many countries. Transgenic maize for commercial production confers either insect resistance or herbicide tolerance or a combination thereof This crop is mainly used for food and livestock feed, and for renewable resources. In case of cultivation of GM maize, the main factors that determine adventitious presence of a Pascher Environ Sci Eur (2016) 28:30 genetically modified organism (GMO) in non-GM material are unintended seed impurity, seed planting equipment and practices, cross-pollination between GM and non-GM crops, the presence of GM volunteers, and product mixing during harvest, transport and/or storage processes [3]. The relevant environmental aspects of volunteer and feral maize include uncontrolled dispersal of GM plants into the environment, prolonged exposure of non-target organisms to GM pollen, increased use of herbicide to remove volunteer and feral maize and an adopted insect resistance management that is mandatory for Bt crops. In the USA, volunteer maize growing in soybean fields above the soybean canopy is known as a highly competitive weed and requires specific herbicide application [6]
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