Location: Crop Protection and Management ResearchTitle: Pollen-mediated dispersal of glyphosate-resistance in Palmer amaranth under field conditions.) Author
Submitted to: Weed Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/11/2012
Publication Date: 3/1/2012
Citation: Sosnoskie, L.M., Webster, T.M., Macrae, A.W., Grey, T.L., Culpepper, A.S. 2012. Pollen-mediated dispersal of glyphosate-resistance in Palmer amaranth under field conditions. Weed Science. 60:366-373. Interpretive Summary: Palmer amaranth (PA) is competitive summer annual weed native to the Southwest US and has recently spread into the Midsouth and Southeastern US. In 2004, glyphosate applied at 12-times the recommended dose failed to control PA in a Georgia field. Currently, glyphosate-resistant (GR) PA infests more than two million ha in 10 states. Within three years of its discovery, GR PA became the greatest threat to the economic sustainability of cotton production. Initiation of biological invasions is often attributed to the movement of progagules into uncolonized habitats outside their native range. Although PA seeds are not adapted for wind dispersal, they may spread by water, animals, or common agricultural activities (e.g. plowing, harvesting). Another less commonly explored aspect of biological invasions is the introductions of alien alleles into a new area. Because PA is wind-pollinated, the GR trait may be highly mobile. PA pollen grains are small and settle slowly out of the air. Results from this study demonstrated that GR-PA dispersed up to 300 m under natural field conditions. Pollen movement can increase the speed with which herbicide resistance develops in a weed population if the rate of outcrossing exceeds the rate of natural genetic mutation. In 2005, GR-PA was confirmed in only one county in Georgia; as of 2011, 65 counties in the state were infested, to some degree with GR-PA. We believe that the rapid development of GR-PA in Georgia was due, in part, to the movement of pollen between spatially segregated populations.
Technical Abstract: In addition to being a strong competitor with cotton and other row crops, Palmer amaranth has developed resistance to numerous important agricultural herbicides, including glyphosate. The objective of this study was to determine if the glyphosate-resistance trait can be transferred via pollen movement from a glyphosate-resistant Palmer amaranth source to a glyphosate susceptible sink. In 2006 and 2007 glyphosate-resistant Palmer amaranth plants were transplanted in the center of a 30 ha field. Glyphosate-susceptible Palmer amaranth plants were transplanted into plots located at distances up to 300 m from the edge of the resistant pollen source in 8 directions. All unwanted Palmer amaranth were eliminated by chemical and physical means. Palmer amaranth seed were harvested from glyphosate-susceptible mother plants, planted in the greenhouse and treated with glyphosate to test resistance status. The proportion of glyphosate-resistant progeny decreased with increased distance from the pollen source; approximately 50 to 60% of the offspring at the 1 and 5 m distances were resistant to glyphosate whereas 20 to 40% of the offspring were resistant at the furthest distances. The development of resistance was not affected by direction; winds were variable with respect to both speed and direction during the peak pollination hours throughout the growing season. Results from this study indicate that the glyphosate-resistance trait can be transferred via pollen movement in Palmer amaranth.