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

Abstract

New switchgrass (Panicum virgatum L.) bioenergy cultivars are being bred through genetic engineering; however, baseline information is urgently needed to establish guidelines for small scale field trials prior to commercialization. In this study, we documented the pattern of pollen mediated gene flow and the extent of seed longevity in field experiments. To mimic crop-to wild, pollen-mediated gene flow, we planted wild recipient switchgrass ramets at various distances away from cultivar donor ramets at two sites in Ohio. Percent hybridization at each distance was estimated from seed set on recipient ramets, which were self-incompatible clones. The pattern of gene flow was best described by negative exponential models, and the minimum isolation distance for a 0.01% gene flow threshold was predicted to be 69 m and 109 m away from the pollen source at the two sites. To investigate seed longevity, we buried seeds of six cultivars and ten wild biotypes in Ohio and Iowa in 2011. A subset of the seeds were exhumed, germinated, and tested for dormancy over three years. Cultivars lost seed viability and dormancy significantly sooner than wild biotypes at both locations in the first year, and most biotypes lost dormancy by the second year. Cultivar seeds buried in the cooler, drier Iowa site had an overall greater longevity than those buried in Ohio. Our findings suggest that substantial amounts of pollen-mediated gene flow could occur in the immediate vicinity of switchgrass pollen sources, and current switchgrass cultivars are unlikely to persist in the seed bank for more than three years.

Pollen dispersal patterns differ among sites for a wind‐pollinated species and an insect‐pollinated species

“…All results were compared to an alpha value of 0.05. Previous research suggests the relationship between Amaranthus tuberculatus pollen dispersal and distance follows an exponential decay pattern (Liu et al, 2012;Sarangi et al, 2017), and this pattern also has been observed in other wind-pollinated herbaceous species (Walsh et al, 2015;Dong et al, 2016;Chang et al, 2018). Although pollen dispersal has not been examined in Solanum lycopersicum, Beckie and Hall (2008) observed that studies modeling the effect of distance from the pollen donor on pollen dispersal in crop plants (e.g., maize, wheat) generally fit exponential decay or inverse power curves to the relationship.…”

Habitat restoration and native grass conservation: a case study of switchgrass (Panicum virgatum)

“…Many additional prairies, CRP areas, and other grasslands were present at varying distances away from each sampled population, and they could introduce new genes through pollen‐ and seed‐dispersal. In a separate study, Chang () assessed the surrounding landscape of the same CRP and prairie areas as this study by estimating the fraction of “CRP land (where cultivars exist)” and “warm‐season grassland (where wild switchgrass may appear)” within 1 km radius from each focal population using a Geographic Information System data collection. Chang () found that the prairies were all isolated with no nearby CRP lands within 1 km radius, except for Rockefeller prairie (no.…”

Long-Distance Pollen Dispersal in Urban Green Roof and Ground-Level Habitats

“…Despite the relatively common use of both exponential decay and inverse power functions to assess pollen dispersal using curve fitting, only two studies have compared them directly. Though Chang et al (2018) concluded that the exponential decay curve was the best fit for Panicum virgatum pollen dispersal patterns at both of two sites, the inverse power curve showed a comparatively high R 2 at one of the sites. And, Barbour et al (2005) concluded that the inverse power curve was the best fit for Eucalyptus nitens pollen dispersal, but the exponential decay curve showed a similarly high R 2 .…”

“…The exponential decay curve was included because it has been used extensively in studies that assessed pollen dispersal patterns using curve fitting (e.g., Beckie and Hall, 2008), including studies on A. tuberculatus (Liu et al, 2012;Sarangi et al, 2017). The inverse power curve also has been used to model pollen dispersal in a range of crop and other species (Beckie and Hall, 2008;Buehler et al, 2012;Chang et al, 2018). The Weibull and logistic curves are not widely used in curve fitting studies, but were included to enable comparisons to the results of the PDF analyses, which included both functions.…”