Seasonal Changes in Undifilum Colonization and Swainsonine Content of Locoweeds

Locoweeds ( and ) are leguminous plants that are toxic due to a symbiotic association with the endophytic fungus . The fungus produces the alkaloid swainsonine, an alpha-mannosidase-inhibitor that causes serious damage to mammals when consumed. A real-time PCR technique was developed to quantify the colonization extent of in locoweeds and to compare it to the swainsonine concentration in the plants. Amplification of the endophyte nuclear ITS region allowed reliable quantification of DNA from field plants and cultures. Swainsonine concentration was highly correlated ( = 0.972, < 0.001) with the proportion of DNA during the first 4 weeks of culture growth. Species of and 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.