Title: Spatial and temporal assessment of pollen- and seed-mediated gene flow from genetically engineered plum Prunus domestica Authors
Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 13, 2013
Publication Date: October 1, 2013
Citation: Scorza, R., Kriss, A.B., Callahan, A.M., Webb, K.K., Demuth, M.A., Gottwald, T.R. 2013. Spatial and temporal assessment of pollen- and seed-mediated gene flow from genetically engineered plum Prunus domestica. PLoS One. 8(10):75291. Interpretive Summary: The movement of pollen from genetically engineered (GE) plants to non-GE plants has been an area of investigation for field crops such as soybean and corn. In these crops, the seed that is formed from the union of the pollen and the egg cell is the part of the crop that is used as both a food and for the planting of the next generation of the crop. Issues of seed purity and organic agriculture standards have fueled debates that have required gene flow studies both through pollen and seed distribution. Plum seeds are not eaten or used in animal feed and plums are not generally seed planted, but are reproduced through grafting. Fruits of non-GE plums that receive GE pollen remain non-GE with only the seed inside the fruit potentially a recipient of the GE trait. Nevertheless, it is still important to measure the movement of pollen and seeds from GE plums to learn their fate in the environment. Our research group has developed a GE plum, ‘HoneySweet’, that is highly resistant to Plum pox virus, one of the most serious diseases affecting plums and other stone fruits. We evaluated both pollen and seed gene flow from ‘HoneySweet’ and other GE plums for 11 years. We found no GE plum seeds outside of the GE orchard. GE pollen flow was, over the entire 11-year-period of the study, to be 0.31 percent or 37 GE positive seeds of 12,116 seeds sampled. When samples were taken from over 650 feet from the GE orchard, the pollen flow dropped to almost zero. Our work shows that coexistence of GE and conventional plums is quite feasible. The benefits of Plum pox virus resistant GE plums can be readily available to plum growers while coexisting with conventional Plum pox virus susceptible orchards, and the GE orchards will be protected from Plum pox virus transmission from susceptible conventional plum orchards.
Technical Abstract: Pollen flow from a 0.46 ha plot of mixed transgenic Prunus domestica located in West Virginia, USA, was evaluated from 2000-2010. Sentinel trees of ‘Italian Prune’ and ‘Seneca‘ plums, which are sexually compatible with the transgenic trees, were planted at distances ranging from 132 to 854 m from the center of the transgenic plum orchard. Larger plots (0.1, 0.25 and 0.5 ha) of mixed plum varieties and seedlings were located at 384, 484 and 998 m from the transgenic plum plot. Beehives (Aphis mellifera) were dispersed between the transgenic plum plot and the pollen flow monitoring sites. Over the 11-year sampling period, 12,116 seeds were assayed for the presence of the uidA (GUS) gene insert, which was present in the transgenic source trees. Gene (pollen) flow out of the transgenic field plot only occurred in four of the 11 years of the study. In the four years when it occurred, gene flow, calculated as the number of GUS positive embryos/total embryos sampled, ranged from 12 percent at 132 m from the center of the transgenic plum plot (29 m from the nearest transgenic plum tree) to 0.4 - 2.2 percent at longer distances (383-998 m). Within the transgenic field plot, gene flow was evaluated in two years and ranged from 4.9 to 39 percent. Spatial modeling indicated that gene flow was dramatically reduced at distances over 200 m from the GE block. Weather data, including temperature, wind, rainfall, relative humidity, and hourly evaporation, were collected during the plum flowering period. Air temperature and rainfall were respectively, positively, and negatively correlated with gene flow reflecting the effects of weather conditions on insect pollinator activity. The location of managed honeybee hives did not have a significant effect on gene flow. Native and naturalized pollinators may have reduced the influence of honeybees as pollinators in the study area. The combined effect of managed bees, and native and naturalized pollinators may have produced a saturation effect of pollinating insects. The data presented demonstrate that gene flow from genetically engineered plums under the conditions of this long-term study can be considered to be low, only occurring at all in less than four of the 11 years of the study and in only 0.31 percent of the total number of seeds analyzed (37/12,116).