ARS | Publication request: Seasonal changes in Undifilum colonization and swainsonine content of locoweeds

Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 5, 2012
Publication Date: April 28, 2012
Citation: Bottger, J.A., Creamer, R., Gardner, D.R. 2012. Seasonal changes in Undifilum colonization and swainsonine content of locoweeds. Journal of Chemical Ecology. 38:486-95.

Interpretive Summary: Some Astragalus and Oxytropis plant species are toxic to livestock and are called locoweeds. These plant contain the toxin identified as swainsonine which occurs from a fungus (Undifilum oxytropis) living with the plant. A technique known as PCR (polymerase chain reaction) was used to develop a new method to measure the degree of colonization of the fungus in the plant material from its DNA. The specifics of the PCR and the measurement of fungus DNA are presented. The method was found to correlate with the concentration of swainsonine in new fungal growth in the lab. Details of the changes in fungus and toxin concentration from Astragalus and Oxytropis plants collected in New Mexico and Colorado over a two year period are presented. In the seasonally sampled plants from the field, high levels of fungus in the plant were associated with high levels of the toxin.

Technical Abstract: Locoweeds (Astragalus and Oxytropis) are leguminous plants that are toxic due to a symbiotic association with the endophytic fungus Undifilum oxytropis. The fungus produces the alkaloid swainsonine, an a-mannosidase-inhibitor that causes serious damage to mammals when consumed. A realtime PCR technique was developed to quantify the colonization extent of Undifilum in locoweeds and to compare it to the swainsonine concentration in the plants. Amplification of the endophyte nuclear ITS region allowed reliable quantification of Undifilum DNA from field plants and in vitro cultures. Swainsonine concentration was highly correlated ('00.972, P<0.001) with the proportion of Undifilum DNA during the first 4 weeks of in vitro culture growth. Species of Astragalus and Oxytropis were sampled seasonally in New Mexico and Colorado for two years. High swainsonine concentration in plant samples was associated with high levels of endophyte DNA, except in plant reproductive tissues.