Low crop plant population densities promote pollen-mediated gene flow in spring wheat (Triticum aestivum L.)

Abstract

Transgenic wheat is currently being field tested with the intent of eventual commercialization. The development of wheat genotypes with novel traits has raised concerns regarding the presence of volunteer wheat populations and the role they may play in facilitating transgene movement. Here, we report the results of a field experiment that investigated the potential of spring wheat plant population density and crop height to minimize gene flow from a herbicide-resistant (HR) volunteer population to a non-HR crop. Pollen-mediated gene flow (PMGF) between the HR volunteer wheat population and four conventional spring wheat genotypes varying in height was assessed over a range of plant population densities. Natural hybridization events between the two cultivars were detected by phenotypically scoring plants in F(1) populations followed by verification with Mendelian segregation ratios in the F(1:2) families. PMGF was strongly associated with crop yield components, but showed no association with flowering synchrony. Maximum observed PMGF was always less than 0.6%, regardless of crop height and density. The frequency of PMGF in spring wheat decreased exponentially with increasing plant population density, but showed no dependence on either crop genotype or height. However, increasing plant densities beyond the recommended planting rate of 300 cropped wheat plants m(-2) provided no obvious benefit to reducing PMGF. Nevertheless, our results demonstrate a critical plant density of 175-200 cropped wheat plants m(-2) below which PMGF frequencies rise exponentially with decreasing plant density. These results will be useful in the development of mechanistic models and best management practices that collectively facilitate the coexistence of transgenic and nontransgenic wheat crops.

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).…”

“…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).…”

Identification of a hybridization window that facilitates sizeable reductions of pollen-mediated gene flow in spring wheat

“…Thus, the study employed a planting regime consisting of two treatments targeting emergence of volunteer plants 100 and 50 GDD before the crop (-100 and -50 GDD), one at crop emergence (0 GDD), and two 50 and 100 GDD following crop emergence. Similar to Willenborg et al (2009a), a paired-pollinator row arrangement was utilized whereby pollinator (volunteer) and source (crop) plants were sown in alternating rows to facilitate the identification of each population. At the third volunteer wheat planting date (0 GDD treatment), the crop was established at a target density of 250 plants m -2 .…”

Thank you for not flowering: conservation genetics and gene flow analysis of native and non-native populations of Fraxinus (Oleaceae) in Ireland

“…Trees are often characterized by longdistance movement of pollen, which is not necessarily homogeneous across the landscape or throughout the flowering season (Bâcles et al, 2005;Byrne et al, 2008). Pollen dispersal has been shown to be influenced by various factors, including population size and density (Willenborg et al, 2009), breeding system (Lowe and Abbott, 2004), flowering phenology (Sampson and Byrne, 2008) and variability in fecundity among individuals (Klein et al, 2008). Consequently, the amount of pollen contamination can be highly variable in space and time between local and alien populations.…”