ARS | Publication request: Relationship between the endophyte embellisia spp. and the toxic alkaloid swainsonine in major locoweed species (Astragalus and Oxytropis)

Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 31, 2007
Publication Date: January 1, 2008
Repository URL: http://www.pprl.ars.usda.gov
Citation: Ralphs, M.H., Creamer, R., Baucom, D., Gardner, D.R., Welch, S.L., Graham, J.D., Hart, C., Cook, D., Stegelmeier, B.L. 2007. Relationship between the endophyte embellisia spp. and the toxic alkaloid swainsonine in major locoweed species (Astragalus and Oxytropis). Journal of Chemical Ecology, Vol. 34 No. 1 pp.32-28 (2008). Published online 12/01/2007 DOI 10.1007/s10886-007-9399-6

Interpretive Summary: The locoweed species that historically caused the majority of locoweed poisoning in the western U.S. were found to contain the fungal endophyte and produced toxic amounts of swainsonine. Astragalus species were generally higher in swainsonine concentration than Oxytropis species. The fungal endophytes associated with Astragalus species may be different species or strains than those in Oxytropis, suggesting strains of endophyte may have differing propensity to synthesize swainsonine. The inability to culture the endophyte from A.m. thompsonii and A. amphioxys, and the inconsistency of detection of the endophyte in varieties of O. lambertii from the previous study, raises questions as to the genetic relationships among some species and varieties in the transmission of the endophyte, or the plants ability to suppress its growth. Further research is required to answer these questions.

Technical Abstract: Locoweeds (Astragalus and Oxytropis spp. which 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 Oxytropis spp. and was shown to produce swainsonine. The objective of this study was to conduct a survey of the major locoweeds from areas where locoweed poisoning has occurred, verify the presence of the endophyte, and compare swainsonine concentration. Species found to contain the fungal endophyte and produce toxic amounts of swainsonine were A. wootoni, A. pubentissimus, A. mollissimus, A. lentiginosus, and O. sericea. Astragalus species generally had higher concentrations of swainsonine than Oxytropis. The endophyte could not be cultured from A. mollissimus var. thompsonii, or A. amphioxys, but was detected by PCR, and only 40% of the 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. The endophyte or swainsonine were not detected in A. cibarius, A. coltonii, or A. filipes.