Pollen-mediated gene flow from transgenic to non-transgenic switchgrass (Panicum virgatum L.) in the field

Abstract

BackgroundSwitchgrass is C4 perennial grass species that is being developed as a cellulosic bioenergy feedstock. It is wind-pollinated and considered to be an obligate outcrosser. Genetic engineering has been used to alter cell walls for more facile bioprocessing and biofuel yield. Gene flow from transgenic cultivars would likely be of regulatory concern. In this study we investigated pollen-mediated gene flow from transgenic to nontransgenic switchgrass in a 3-year field experiment performed in Oliver Springs, Tennessee, U.S.A. using a modified Nelder wheel design. The planted area (0.6 ha) contained sexually compatible pollen source and pollen receptor switchgrass plants. One hundred clonal switchgrass ‘Alamo’ plants transgenic for an orange-fluorescent protein (OFP) and hygromycin resistance were used as the pollen source; whole plants, including pollen, were orange-fluorescent. To assess pollen movement, pollen traps were placed at 10 m intervals from the pollen-source plot in the four cardinal directions extending to 20 m, 30 m, 30 m, and 100 m to the north, south, west, and east, respectively. To assess pollination rates, nontransgenic ‘Alamo 2’ switchgrass clones were planted in pairs adjacent to pollen traps.ResultsIn the eastward direction there was a 98% decrease in OFP pollen grains from 10 to 100 m from the pollen-source plot (Poisson regression, F1,8 = 288.38, P < 0.0001). At the end of the second and third year, 1,820 F1 seeds were collected from pollen recipient-plots of which 962 (52.9%) germinated and analyzed for their transgenic status. Transgenic progeny production detected in each pollen-recipient plot decreased with increased distance from the edge of the transgenic plot (Poisson regression, F1,15 = 12.98, P < 0.003). The frequency of transgenic progeny detected in the eastward plots (the direction of the prevailing wind) ranged from 79.2% at 10 m to 9.3% at 100 m.ConclusionsIn these experiments we found transgenic pollen movement and hybridization rates to be inversely associated with distance. However, these data suggest pollen-mediated gene flow is likely to occur up to, at least, 100 m. This study gives baseline data useful to determine isolation distances and other management practices should transgenic switchgrass be grown commercially in relevant environments.Electronic supplementary materialThe online version of this article (doi:10.1186/s12896-017-0363-4) contains supplementary material, which is available to authorized users.

Extent of pollen-mediated gene flow and seed longevity in switchgrass (Panicum virgatum L.): Implications for biosafety procedures

“…Our findings suggest that crop-to-wild hybridization in switchgrass could occur beyond 100 m from a relatively small donor source (~100 plants). Our findings of pollen-mediated gene flow in switchgrass are consistent with those of Millwood et al [28], who employed a similar design to study crop-to-crop gene flow in switchgrass. Based on our estimation, to prevent pollenmediated gene flow to conspecific relatives, at least 109 m of minimum isolation distance is recommended for a small field trial of transgenic switchgrass in an open field.…”

“…For example, the extent and variability of pollen-mediated gene flow in switchgrass under field conditions have only been recently described in the literature [28]. The pattern of pollenmediated gene flow is dictated by numerous factors, for instance, climatic conditions, pollination biology, and size and proximity of source and recipient populations; therefore, patterns of gene flow are expected to vary in different landscapes [29][30][31].…”

“…As 2G bioenergy crops go forward, the USDA has demanded more thorough ecological studies for making regulatory decisions [22,23,28,29,33]. Specifically, data are needed to characterize the minimum isolation distance between switchgrass carrying novel transgenes and sexually compatible relatives, and the longevity of these seeds when left in the soil.…”

Gene flow in commercial alfalfa (Medicago sativa subsp. sativa L.) seed production fields: Distance is the primary but not the sole influence on adventitious presence

“…Pollen viability, the length of time pollen remains viable after being picked up by a pollinator, will affect gene flow potential [ 39 ]. Environmental factors can affect flower density and duration, and pollinator behavior [ 20 – 22 , 36 , 40 – 43 ]. Low water availability decreases flower production which negatively impacts the resources provided by the plants to the bees [ 44 , 45 ].…”

Combining rare alleles and grouped pollen donors to assign paternity in pollen dispersal studies

“…These methods typically involve either trapping or tracking pollen grains. For example, pollen traps (Millwood et al., ), fluorescent‐dyed pollen analogues (Waser and Price, ; Van Geert et al., , ; Van Rossum et al., ), and tracking pollinator movements (Pasquet et al., ) are widely used to assess pollen movement. However, each approach has logistical or methodological constraints that limit their utility for assessing pollen movement patterns (Thomson et al., ; Adler and Irwin, ; Pasquet et al., ; Ashley, ).…”