Pollen-mediated gene flow in wheat (Triticum aestivum L.) in a semiarid field environment in Spain

Abstract

Transgenic wheat (Triticum aestivum L.) varieties are being developed and field-tested in various countries. Concerns regarding gene flow from genetically modified (GM) crops to non-GM crops have stimulated research to estimate outcrossing in wheat prior to the release and commercialization of any transgenic cultivars. The aim is to ensure that coexistence of all types of wheat with GM wheat is feasible in accordance with current regulations. The present study describes the result of a field experiment under the semi-arid climate conditions of Madrid, Spain, at two locations ("La Canaleja" and "El Encin" experimental stations) in Madrid over a 3-year period, from 2005 to 2007. The experimental design consisted of a 50 × 50 m wheat pollen source sown with wheat cultivars resistant to the herbicide chlortoluron ('Deganit' and 'Castan' respectively) and three susceptible receptor cultivars ('Abental', 'Altria' and 'Recital') sown in replicated 1 × 1 m plots at different distances (0, 1, 3, 5, 10, 20, 40, 80 and 100 m) and four directions. Outcrossing rates were measured as a percentage of herbicide-resistant hybrids using an herbicide-screening assay. Outcrossing was greatest near the pollen source, averaging 0.029% at 0 m distance at "La Canaleja" and 0.337% at "El Encin", both below the 0.9% European Union regulated threshold, although a maximum outcrossing rate of 3.5% was detected in one recipient plot. These percentages declined rapidly as the distance increased, but hybrids were detected at different rates at distances of up to 100 m, the maximum distance of the experiment. Environmental conditions, as drought in 2004-2005 and 2005-2006, may have influenced the extent of outcrossing. These assays carried out in wheat under semi-arid conditions in Europe provide a more complete assessment of pollen-mediated gene flow in this crop.

Assessment of the pollen-mediated transgene flow from the plants of herbicide resistant wheat to conventional wheat (Triticum aestivum L.)

“…Even in the worst case the pollen mediated transgene flow rates were always below the value of 1 %, which is the strictest threshold adopted to determine GMO admixture for feed and food in the international trade (EC No 1828/2003). This result is in accordance with the results of previous studies conducted by different authors to ensure seed purity in which the range of outcrossing frequencies averaged around 1 % (MatusCádiz et al 2004;Hanson et al 2005;Gaines et al 2007;Willenborg et al 2009;Loureiro et al 2012). Undoubtedly when donor and recipient wheat plant are bagged together or grown in adjacent rows at a 'zero distance' the highest possible outcrossing could be rather high, up to 8.5-10.6 % (Lawrie et al 2006;Rieben et al 2011).…”

“…With increasing distances to the pollen source the gene flow frequency declined rapidly even for commercialscale fields. Matus-Cádiz et al (2004) reported the reduction of maximal gene flow rate in Canadian wheat varieties from 0.44 % at a distance of 0.2 m to 0.01 % at a distance of 60-100 m. The similar result was obtained by Loureiro et al (2012) for Spanish wheat cultivars. In their experiments the average gene flow rate fell from 0.02 to 0.62 % at 0 m to 0.00-0.02 % at 100 m. Hanson et al (2005) found only single outcrossing events at 29 and 42 m from the pollen source, while the maximum gene flow (0.45 %) was detected only when plants were grown closest to the blue aleurone pollen source.…”

“…Undoubtedly when donor and recipient wheat plant are bagged together or grown in adjacent rows at a 'zero distance' the highest possible outcrossing could be rather high, up to 8.5-10.6 % (Lawrie et al 2006;Rieben et al 2011). Nevertheless it is important to point out that transgene flow frequencies reduced dramatically with the increase of the distance from pollen source and up to recipient plants (Matus-Cádiz et al 2004;Hanson et al 2005;Matus-Cádiz et al 2007;Beckie et al 2011;Loureiro et al 2012). In the present study the considerable decrease of transgene flow frequencies (up to\0.01) was observed when the distance was increased up to 5 m.…”

“…In most studies, at the distance below 1 m the average gene flow frequencies were reported to be under 1 % (Matus-Cádiz et al 2004;Hanson et al 2005;Gaines et al 2007;Willenborg et al 2009;Loureiro et al 2012). In close proximity (0-30 cm) higher gene flow rates up to 10.6 % have been reported (Hucl and Matus-Cádiz 2001;Matus-Cádiz et al 2004;Lawrie et al 2006).…”

“…Due to regulatory constrains the measurement of gene flow in the most experiments was carried out without the use of GM wheat by planting non transgenic wheat varieties possessing homozygous dominant gene markers, such as the blue-aleurone trait (Matus-Cádiz et al 2004;Hanson et al 2005), imidazolinone resistance trait (Gaines et al 2007;Willenborg et al 2009;Beckie et al 2011) or chlortoluron tolerance trait (Loureiro et al 2012). Usually both circular and rectangular field experimental designs are adopted to monitor gene flow (Mallory-Smith et al 2015).…”