Relationship Between the Endophyte Embellisia spp. and the Toxic Alkaloid Swainsonine in Major Locoweed Species (Astragalus and Oxytropis) M. H. Ralphs & R. Creamer & D. Baucom & D. R. Gardner & S. L. Welsh & J. D. Graham & C. Hart & D. Cook & B. L. Stegelmeier Received: 27 August 2007 / Revised: 30 October 2007 / Accepted: 31 October 2007 / Published online: 1 December 2007 # US Government: Agricultural Research Service 2007 Abstract Locoweeds (Astragalus and Oxytropis spp. that contain the toxic alkaloid swainsonine) cause widespread poisoning of livestock on western rangelands. There are 354 species of Astragalus and 22 species of Oxytropis in the US and Canada. Recently, a fungal endophyte, Embellisia spp., was isolated from Astragalus and Oxy- tropis spp. and shown to produce swainsonine. We conducted a survey of the major locoweeds from areas where locoweed poisoning has occurred to verify the presence of the endophyte and to relate endophyte infection with swainsonine concentrations. Species found to contain the fungal endophyte and produce substantial amounts of swainsonine were A. wootoni, A. pubentissimus, A. mollis- simus, A. lentiginosus, and O. sericea. Astragalus species generally had higher concentrations of swainsonine than Oxytropis. Swainsonine was not detected in A. alpinus, A. cibarius, A. coltonii, A. filipes, or O. campestris. The endophyte could not be cultured from A. mollissimus var. thompsonii or A. amphioxys, but was detected by polymer- ase chain reaction, and only 30% of these samples contained trace levels of swainsonine. Further research is necessary to determine if the endophyte is able to colonize these and other species of Astragalus and Oxytropis and determine environmental influences on its growth and synthesis of swainsonine. Keywords Locoweed . Astragalus wootoni . Astragalus pubentissimus . Astragalus mollissimus . Astragalus lentiginosus . Oxytropis sericea . Swainsonine . Poisonous plant . Livestock poisoning Introduction Historically, locoweeds (Astragalus and Oxytropis spp. that contain the toxic alkaloid swainsonine) have caused wide- spread livestock losses on western rangelands (Kingsbury 1964), and they remain a major impediment to livestock production (Ralphs et al. 2002a). There are 354 species of Astragalus and 22 species of Oxytropis in the US and Canada (Welsh et al. 2007a), and Astragalus and Oxytropis plants occur in every major plant community on western rangelands. Only 24 species in North America have been verified to contain swainsonine or have a history of causing locoism (Ralphs et al. 2002a). Recently, a fungal endophyte, Embellisia spp. Pleospor- aceae, was isolated from Astragalus and Oxytropis spp. and J Chem Ecol (2008) 34:32–38 DOI 10.1007/s10886-007-9399-6 M. H. Ralphs (*) : D. R. Gardner : D. Cook : B. L. Stegelmeier USDA/ARS Poisonous Plant Research Laboratory, 1150 E. 1400 N., Logan, UT 84341, USA e-mail: Michael.Ralphs@ars.usda.gov R. Creamer : D. Baucom Department Entomology, Plant Pathology and Weed Science, New Mexico State University, Las Cruces, NM 88003, USA J. D. Graham New Mexico State University, Extension Service, Clayton, NM 88415, USA S. L. Welsh Bean Natural History Museum, Brigham Young University, Provo, UT 84602, USA C. Hart Texas A&M University Research and Extension Center, Stephenville, TX 76401, USA