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Locoweeds are defined as Astragalus and Oxytropis species that cause intoxication due to the alkaloid swainsonine. Swainsonine concentrations in Oxytropis sericea were influenced by location, plant part, and the developmental stage of the plant. Concentrations followed similar trends at each location, generally increasing over the growing season in above-ground parts until the plant reaches maturity with no change in concentration in the crowns. At the onset of senescence, swainsonine decreased in floral parts to less than half of the peak concentration. Similar to swainsonine concentrations, endophyte amounts were influenced by location, plant part, and the developmental stage of the plant. Likewise, endophyte amounts generally increased over the growing season in above ground parts and remained static in the crowns at all four locations. Swainsonine in Oxytropis sericea was positively associated with the endophyte Undifilum, which is responsible for swainsonine biosynthesis.

Locoweeds are Astragalus and Oxytropis species that contain the toxic alkaloid swainsonine. Swainsonine accumulates in all parts of the plant with the highest concentrations found in the above ground parts. A fungal endophyte, Undifilum oxytropis, found in locoweed plant species, is responsible for the synthesis of swainsonine. By using quantitative PCR, the endophyte can be quantified in locoweed species. Endophyte amounts differ between plant parts and in some instances do not mirror the concentrations of swainsonine in the corresponding parts. Two groups of Oxytropis sericea were identified: one that accumulated high concentrations of swainsonine and another where swainsonine was not detected, or concentrations were near the detection threshold. The plants with high swainsonine concentrations had quantitatively higher amounts of endophyte. Alternatively, plants with low or no swainsonine detected had quantitatively lower endophyte amounts. In addition, swainsonine and endophyte concentrations were not distributed uniformly within the same plant when separated into stalks (leaves, scape(s), and flowers/pods). These findings provide evidence as to why plants in the same population accumulate different concentrations of swainsonine, and they have important implications for sampling of locoweed plants.

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 Oxytropis 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. mollissimus, 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 polymerase 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.