Field Crops Research 178 (2015) 69–76 Contents lists available at ScienceDirect Field Crops Research jou rn al hom epage: www.elsevier.com/locate/fcr Quantifying transgene flow rate in transgenic Sclerotinia-resistant peanut lines Jiahuai Hu a , Darcy E.P. Telenko a , Patrick M. Phipps a , Holly Hills b , Elizabeth A. Grabau b,∗ a Tidewater Agricultural Research & Extension Center (AREC), Virginia Tech, Suffolk, VA 23437, USA b Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA 24061, USA a r t i c l e i n f o Article history: Received 10 February 2015 Received in revised form 19 March 2015 Accepted 20 March 2015 Keywords: Outcrossing Oxalate oxidase Barley Pollination Risk assessment a b s t r a c t Multi-year transgenic field trials were conducted to assess the extent of pollen-mediated transgenic flow in Virginia to support a petition requesting deregulated status for Blight Blocker peanuts from USDA Animal and Plant Health Inspection Service (APHIS) Biotechnology Regulatory Services (BRS). We measured transgene flow from transgenic lines to their non-transgenic parental cultivars. A colorimetric method based on quantification of hydrogen peroxide released from oxalic acid in the presence of the oxalate oxidase was used to screen seed embryos from non-transgenic rows at various distances from the transgenic source. The overall transgene flow rate in three cultivars was 0.2094% based on screening over 85,000 seeds. In general, the transgene flow rate greatly declined past 10 m from the transgene source. However, a transgene flow rate of less than 0.05% did occur sporadically at greater distances than 10 m. In conclusion, transgene flow in peanut can be spatially confined to provide negligible rates using relatively short separation distances. The extremely low rate of transgene flow at greater distance was dependent on ecological and environmental contexts, particularly on foraging patterns and flight distance of pollinators. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Peanut (Arachis hypogaea L.) is a major agronomic crop culti- vated in over 100 countries. The total production area worldwide was 25.4 million ha in 2014 (FAO, 2013). Peanut is not only a rich source of oil (44–55%), protein (20–50%) and carbohydrates (10–20%), but also a nutritional source of niacin, folate, calcium, magnesium, zinc, iron, phosphorus, riboflavin, thiamine and vita- min E. It is an important commodity for the U.S. economy and crucial to the subsistence of millions of small farmers in Asia and Africa. Sclerotinia blight, caused by Sclerotinia minor Jagger, was first discovered in Argentina and is a major disease of peanut world- wide including the U.S. (Porter and Melouk, 1997). There are few resistance genes present in the germplasm of breeding lines and commercial cultivars. Rice chitinase and alfalfa -1-3-glucanase have been transformed into peanut and showed resistance to the disease (Chenault et al., 2002). We have transformed three Virginia- type peanut cultivars (NC 7, Wilson, and Perry) with a barley oxalate oxidase gene resulting in high levels of resistance to Sclerotinia blight (Hu et al., 2014; Livingstone et al., 2005; Partridge-Telenko ∗ Corresponding author. Tel.: +1 540 231 7876; fax: +1 540 231 7477. E-mail address: egrabau@vt.edu (E.A. Grabau). et al., 2011). A 2008 abstract reported the cloning of sequences similar to oxalate oxidase (Chen et al., 2008) but no oxalate oxi- dase enzyme activity has been reported or observed in any peanut cultivars that we have assayed. Oxalate oxidase is ubiquitous in monocotyledonous crops such as barley and wheat (Bernier and Berna, 2001) and has been safely consumed by humans in cereal grains for centuries. The presence of the exogenous barley oxalate oxidase in peanuts should not pose additional food or feed safety issues. We have demonstrated substantial compositional equiva- lence between Blight blocker peanuts and non-transgenic peanut (Hu et al., 2014). The transgenic lines are pending submission to U.S. regulatory agencies. Accurate quantification of transgene flow is a consideration in the environmental risk and biosafety assessment prior to their safe release and commercial use of transgenic crops. Gene flow is defined as “successful transfer of genetic information between dif- ferent individuals, populations and generations (to progeny) and across spatial dimensions” (CAST, 2007). Gene flow in transgenic crops involves dispersal of pollen or seeds to conventional agricul- tural fields or wild relatives. Domesticated peanuts lack invasive potential and thus are not considered to be a significant weed (Andersson and de Vicente, 2010). Outcrossing from domesticated peanut to the only sexually compatible wild relative (Arachis mon- ticola) is not a concern in the U.S. because the only ecological niche http://dx.doi.org/10.1016/j.fcr.2015.03.016 0378-4290/© 2015 Elsevier B.V. All rights reserved.